MXPA00008441A

MXPA00008441A - Deeply reduced oxidation catalyst and its use for catalyzing liquid phase oxidation reactions

Info

Publication number: MXPA00008441A
Application number: MXPA/A/2000/008441A
Authority: MX
Inventors: R Ebner Jerry; A Leiber Mark; Wan Kamto; E Rogers Peter; Liu Jingyue; Woods Anthony
Original assignee: Monsanto Technology Llc
Priority date: 1998-02-25
Filing date: 2000-08-25
Publication date: 2001-07-09

Abstract

This invention relates to an improved catalyst, comprising a carbon support having a noble metal at its surface, for use in catalyzing liquid phase oxidation reactions, especially in an acidic oxidative environment and in the presence of solvents, reactants, intermediates, or products which solubilize noble metals;a process for the preparation of theimproved catalyst;a liquid phase oxidation process using such a catalyst wherein the catalyst exhibits improved resistance to noble metal leaching, particularly in acidic oxidative environments and in the presence of solvents, reactants, intermediates, or products which solubilize noble metals;and a liquid phase oxidation process in which N-(phosphonomethyl)iminodiacetic acid (i.e.,"PMIDA") or a salt thereof is oxidized to form N-(phosphonomethyl)glycine (i.e.,"glyphosate") or a salt thereof using such a catalyst wherein the oxidation of the formaldehyde and formic acid by-products into carbon dioxide and water is increased.

Description

INTENSELY REDUCED OXIDATION CATALYST AND ITS USE TO CATALYZE LIQUID PHASE OXIDATION REACTIONS BACKGROUND OF THE INVENTION In general terms, this invention relates to an improved oxidation catalyst and to its use to catalyze oxidation reactions in the liquid phase, especially in acidic oxidative media and in the presence of reagents, intermediates, products or solvents that solubilize noble metals. In a preferred embodiment, the present invention relates to an improved oxidation catalyst and to a process in which the catalyst is used to convert N- (phosphonomethyl) iminodiacetic acid, or a salt thereof, to N- (phosphonomethyl) glycine or a salt of it. Franz, in the patent of E.U.A. No. 3,799, 758, describes N- (phosphonomethyl) glycine (known in the agricultural chemical industry as "glyphosate"). The N- (phosphonomethyl) glycine and its salts are conveniently applied as postemergent herbicides in an aqueous formulation. It is a very effective broad spectrum and commercially important herbicide, useful to destroy or control a wide variety of plants, including germinating seeds, emerging seedlings, woody and herbaceous maturing and established vegetation, and aquatic plants. Various methods for preparing N- (phosphonomethyl) glycine are known in the art. Franz (US Patent No. 3,950,402) teaches that N- (phosphonomethyl) glycine can be prepared by means of the liquid phase oxidative decomposition of N- (phosphonomethyl) iminodacetic acid (sometimes referred to as "PMIDA") with oxygen, in the presence of a catalyst comprising a noble metal deposited on the surface of an activated carbon support: noble metal over carbon catalyst (HO) 2P (O) CH2N (CH2CO2H) 2 + 1/2 O2 > (HO) 2P (O) CH2NHCH2CO2H + CO2 + HCHO Other by-products can also be formed, such as formic acid which is formed by the oxidation of the formaldehyde by-product, and aminomethylphosphonic acid ("AMPA") which is formed by the oxidation of N- (phosphonomethyl) glycine. Although the Franz method produces an acceptable yield and purity of N- (phosphonomethyl) glycine, high losses of the expensive noble metal are caused in the reaction solution (ie, "leaching") because, under the oxidation conditions of the reaction, part of the noble metal is oxidized to a more soluble form, and both the PMIDA and the N- (phosphonomethyl) glycine act as ligands that solubilize the noble metal. In U.S. Patent No. 3,969,938, Hershman teaches that activated carbon can be used alone, in the presence of a noble metal, to effect oxidative decomposition of PMIDA to form N- (phosphonomethyl) glycine. In U.S. Patent No. 4,624,937, Chou further teaches that the activity of the carbon catalyst taught by Hershman can be increased by removing the oxides from the surface of the carbon catalyst before using it in the oxidation reaction. See also the patent of E.U.A. No. 4,696,772, which provides a separate discussion by Chou regarding the increased catalyst activity of carbon removing oxides from the surface of the carbon catalyst. Although, of course, these procedures do not have metal leaching noble, do not tend to produce higher concentrations of by-product formaldehyde when they are used to effect catalytic decomposition of N- (phosphonomethyl) iminodiacetic acid. This by-product of formaldehyde is inconvenient since it reacts with N- (phosphonomethyl) glycine to produce undesirable byproducts (mainly N-methyl-N- (phosphonomethyl) glycine, sometimes referred to as "NMG"), which reduce the yield of N- (phosphonomethyl) glycine. In addition, the by-product formaldehyde alone is undesirable because of its potential toxicity. See Smith, patent of E.U.A. No. 5,606,107. Optimally, therefore, it has been suggested that formaldehyde can be oxidized simultaneously to carbon dioxide and water as the PMIDA is oxidized to N- (phosphonomethyl) glycine in a single reactor, thus giving the following reaction: catalyst + O2 (HO) 2P (O) CH2N (CH2CO2H) 2 >; (HO) 2P (O) CH2NHCH2CO2H + 2CO2 + H2O As the above teachings suggest, this procedure requires the presence of both carbon (which primarily effects the oxidation of PMIDA to form N- (phosphonomethyl) glycine and formaldehyde) and a noble metal (which mainly effects the oxidation of formaldehyde to form carbon dioxide and water). However, previous attempts to develop a stable catalyst for said oxidation process have not been completely satisfactory. As Franz, Ramón and others (U.S. Patent No. 5,179,228) teach the use of a noble metal deposited on the surface of a carbon support. To reduce the leaching problem (which Ramón and others report up to 30% loss of noble metal per cycle), however, Ramón and others teach to flood the reaction mixture with nitrogen under pressure after finishing the oxidation reaction for cause redeposition of the noble metal on the surface of the carbon support. According to Ramón and others, flooding with nitrogen reduces the loss of noble metal to less than 1%. Even so, the amount of loss of noble metal produced with this method is unacceptable. In addition, the redeposition of noble metal can lead to loss of surface area of the noble metal, which in turn, reduces the activity of the catalyst. Using a different approach, Felthouse (U.S. Patent No. 4,582,650) teaches the use of two catalysts: (i) an activated carbon to effect the oxidation of PMIDA in N- (phosphonomethyl) glycine, and (ii) a cocatalyst to concurrently perform the oxidation of formaldehyde of carbon dioxide and water. The cocatalyst consists of an aluminosilicate support having a noble metal located within its pores. The pores are dimensioned to exclude N- (phosphonomethyl) glycine and thereby prevent the noble metal of the cocatalyst from being poisoned with N- (phosphonomethyl) glycine. According to Felthouse, the use of these two catalysts together allows the simultaneous oxidation of PMIDA to N- (phosphonomethyl) glycine and of formaldehyde to carbon dioxide and water. However, this approach has several disadvantages: (1) it is difficult to recover the expensive noble metal from the aluminosilicate support for reuse; (2) it is difficult to design two catalysts in such a way as to equal the proportions between them; (3) The carbon support, which has no noble metal deposited on its surface, tends to deactivate at a rate that can exceed 10% per cycle. Thus, there is a need for an improved multiple reaction catalyst and reaction process that oxidizes PMIDA to N- (phosphonomethyl) glycine, simultaneously exhibiting noble metal leaching resistance and increased oxidation of formaldehyde in carbon dioxide and water ( that is, increased formaldehyde activity).

BRIEF DESCRIPTION OF THE INVENTION This invention provides an improved catalyst for use in the catalysis of oxidation reactions in the liquid phase, especially in an acidic oxidative medium and in the presence of solvents, reagents, intermediates or products that solubilize noble metals; a process for the preparation of the improved catalyst; a liquid phase oxidation process using said catalyst, in which the catalyst exhibits improved resistance to noble metal leaching, particularly in acidic oxidative media and in the presence of solvents, reagents, intermediates or products that solubilize noble metals; and a liquid phase oxidation process in which PMIDA or a salt thereof is oxidized to form N- (phosphonomethyl) glycine or a salt thereof using said catalyst, wherein the oxidation of the formaldehyde by-product is increased. Therefore, briefly, the present invention is directed to a novel oxidation catalyst comprising a carbon support having a noble metal on its surface. In one embodiment, the catalyst is characterized in that it produces no more than about 0.7 mmoles of carbon monoxide per gram of catalyst when a dry sample of the catalyst is heated in a helium atmosphere at a temperature of from about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for about 30 minutes. In another embodiment directed to an oxidation catalyst comprising a carbon support having a noble metal on its surface, the carbon support also has a promoter on the surface. The catalyst is characterized in that it produces no more than about 0.7 mmoles of carbon monoxide per gram of catalyst when a dry sample of the catalyst, after having been heated to a temperature of about 500 ° C for about one hour in a hydrogen atmosphere, and before being exposed to an oxidant after heating in the hydrogen atmosphere, it is heated in a helium atmosphere at a temperature from about 20 ° C to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for about 30 minutes. In another embodiment directed to an oxidation catalyst comprising a carbon support having a noble metal on its surface, the support also has carbon and oxygen on the surface. The ratio of carbon atoms to oxygen atoms on the surface, is at least about 30: 1, as measured by X-ray photoelectron spectroscopy. In another embodiment directed to an oxidation catalyst comprising a carbon support having a noble metal on its surface, the support also has a promoter, carbon and oxygen on the surface. The catalyst is characterized by having a ratio of carbon atoms to oxygen atoms of at least about 30: 1 on the surface, as measured by X-ray photoelectron spectroscopy after heating the catalyst at a temperature of about 500 ° C for about one time in a hydrogen atmosphere, and before exposing the catalyst to an oxidant after heating in the hydrogen atmosphere. In another embodiment directed to an oxidation catalyst comprising a carbon support having a noble metal on its surface, the support also has a surface layer having a thickness of about 50 A, measured inward from the surface. This surface layer comprises oxygen and carbon, the ratio of carbon atoms to oxygen atoms in the surface layer being at least about 30: 1. In another embodiment directed to an oxidation catalyst comprising a carbon support having a noble metal on its surface, the support also has a promoter on the surface. In addition, the support has a surface layer having a thickness of approximately 50 A measured inward from the surface, and comprises carbon and oxygen. In this embodiment, the catalyst is characterized by having a ratio of carbon atoms to oxygen atoms in the surface layer of at least about 30: 1, as measured by X-ray photoelectron spectroscopy after heating the catalyst to a temperature of about 500 ° C for about one hour in a hydrogen atmosphere, and before exposing the catalyst to an oxidant after heating in the hydrogen atmosphere. In another embodiment directed to an oxidation catalyst comprising a carbon support having a noble metal on its surface, the catalyst is prepared by means of a process comprising depositing a noble metal on the surface, and then heating the surface to a temperature greater than about 500 ° C. In another embodiment directed to an oxidation catalyst comprising a carbon support having a noble metal on its surface, the catalyst is prepared by means of a process comprising depositing a noble metal on the surface, and then heating the surface to a temperature of at least about 400 ° C. In this embodiment, before the deposition of the noble metal, the carbon support has carbon and oxygen on its surface in amounts such that the ratio of carbon atoms to oxygen atoms on the surface is at least about 20: 1 , as measured by X-ray photoelectron spectroscopy. In another embodiment directed to an oxidation catalyst comprising a carbon support having a noble metal on its surface, the catalyst is prepared by a process comprising depositing a noble metal on the surface, and then exposing the surface to a reducing medium. Again here, before the deposition of the noble metal, the carbon support has carbon and oxygen on its surface in amounts such that the ratio of carbon atoms to oxygen atoms on the surface is at least about 20: 1, measured by X-ray photoelectron spectroscopy.

This invention is also directed to a process for the preparation of an oxidation catalyst. In one embodiment of this invention, the method comprises depositing a noble metal on a surface of a carbon support and then heating the surface to a temperature greater than about 500 ° C. In another embodiment directed to a process for the preparation of an oxidation catalyst, the catalyst is prepared from a carbon support having carbon and oxygen on a surface of the carbon support. The process comprises depositing a noble metal on the surface of the carbon support and then exposing the surface to a temperature of at least about 400 ° C. In this embodiment, before the deposition of the noble metal, the ratio of carbon atoms to oxygen atoms on the surface of the carbon support is at least about 20: 1, as measured by X-ray photoelectron spectroscopy. modality directed to a process for the preparation of an oxidation catalyst, the catalyst is prepared from a carbon support having carbon and oxygen on a surface of the carbon support. The process comprises depositing a noble metal on the surface of the carbon support and then exposing the surface to a reducing medium. In this embodiment, before the deposition of the noble metal, the ratio of carbon atoms to oxygen atoms on the surface of the carbon support is at least about 20: 1 as measured by X-ray photoelectron spectroscopy. In another embodiment directed to a process for the preparation of an oxidation catalyst, the catalyst is prepared from a carbon support having carbon and oxygen on its surface. The method comprises depositing a noble metal on the surface, and then exposing the surface to a reducing means to reduce the surface in such a way that the ratio of carbon atoms to oxygen atoms on the surface is at least about 30: 1 measured by X-ray photoelectron spectroscopy. In another embodiment directed to a process for the preparation of an oxidation catalyst, the method comprises depositing a noble metal on a surface of a carbon support, and then exposing the surface to a reducing medium. to reduce the surface area such that no more than about 0.7 mmoles of carbon monoxide per gram of catalyst are desorbed from the catalyst when a dry sample of the catalyst is heated in a helium atmosphere at a temperature of about 20 to about 900 °. C, at a rate of about 10 ° C per minute, and then at a temperature of about 9 00 ° C for about 30 minutes. This invention is also directed to a process for oxidizing a reagent in a mixture (typically a solution or suspension) and very typically a solution wherein the mixture has the ability to solubilize a noble metal. This method comprises contacting the mixture with an oxidation catalyst in the presence of oxygen. In one embodiment, the catalyst comprises a carbon support having a noble metal on its surface. The catalyst is characterized in that it produces no more than about 1.2 mmol of carbon monoxide per gram of catalyst when a dry sample of the catalyst is heated in a helium atmosphere at a temperature of about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for about 30 minutes. In another embodiment directed to the process for oxidizing a reagent in a mixture that can solubilize a noble metal, the catalyst comprises a carbon support having a noble metal and a promoter on a surface of the carbon support. In addition, the catalyst is characterized in that it produces no more than about 1.2 mmoles of carbon monoxide per gram of catalyst when a dry sample of the catalyst, after being heated to a temperature of about 500 ° C for about one hour in a hydrogen atmosphere, and before being exposed to an oxidant after heating in the hydrogen atmosphere, it is heated in a helium atmosphere at a temperature from about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for about 30 minutes. In another embodiment directed to the process for oxidizing a reagent in a mixture that can solubilize a noble metal, the catalyst comprises a carbon support having a noble metal, carbon and oxygen on a surface of the carbon support. The ratio of carbon atoms to oxygen atoms on the surface is at least 20: 1, as measured by X-ray photoelectron spectroscopy. In another embodiment directed to the method for oxidizing a reagent in a mixture that can solubilize a noble metal, the catalyst comprises a carbon support having a noble metal, a promoter, carbon and oxygen on a surface of the carbon support. The catalyst is characterized by having a ratio of carbon atoms to oxygen atoms on the surface, which is at least about 20: 1, as measured by X-ray photoelectron spectroscopy after heating the catalyst to a temperature of about 500 °. C for about one hour in a hydrogen atmosphere, and before exposing the catalyst to an oxidant after heating in the hydrogen atmosphere. In another embodiment directed to the process for oxidizing a reagent in a mixture that can solubilize a noble metal, the catalyst comprises a carbon support having a noble metal on a surface of the carbon support. In addition, the support comprises a surface layer having a thickness of about 50 A, measured inward from the surface, and comprising oxygen and carbon. The ratio of carbon atoms to oxygen atoms in the surface layer is at least about 20: 1, as measured by X-ray photoelectron spectroscopy. In another embodiment directed to the method for oxidizing a reagent in a mixture that can solubilize a noble metal, the catalyst comprises a carbon support having: (a) a noble metal and a promoter on a surface of the carbon support; (b) and a surface layer having a thickness of approximately 50 A, measured inward from the surface, and comprises carbon and oxygen. The catalyst is characterized by having a ratio of carbon atoms to oxygen atoms in the surface layer, of at least about 20: 1, as measured by X-ray photoelectron spectroscopy after heating the catalyst to a temperature of about 500 °. C for about one hour in a hydrogen atmosphere, and before exposing the catalyst to an oxidant after heating in the hydrogen atmosphere. In another embodiment directed to the process for oxidizing a reagent in a mixture that can solubilize a noble metal, the catalyst is prepared by means of a process comprising depositing a noble metal on a surface of a carbon support, and then heating the surface to a temperature of at least about 400 ° C.

In another embodiment directed to the process for oxidizing a reagent in a mixture that can solubilize a noble metal, the catalyst is prepared by a process comprising depositing a noble metal on a carbon surface and then exposing the surface to a reducing medium. In this embodiment, before the deposition of noble metal, the carbon support has carbon and oxygen on its surface in quantities such that the ratio of carbon atoms to oxygen atoms on the surface is at least 20: 1, as measured by X-ray photoelectron spectroscopy. This invention is also directed to a process for the preparation of N- (phosphonomethyl) glycine or a salt thereof. The process comprises contacting N- (phosphonomethyl) iminodiacetic acid, or a salt thereof, with an oxidation catalyst in the presence of oxygen. In one embodiment, the catalyst comprises a carbon support having a noble metal on a surface of the carbon support. The catalyst is characterized in that it produces no more than about 1.2 mmoles of carbon monoxide per gram of catalyst when a dry sample of the catalyst is heated in a helium atmosphere at a temperature of from about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for 30 minutes. In another embodiment directed to the process for the preparation of N- (phosphonomethyl) glycine or a salt thereof, the catalyst comprises a carbon support having a noble metal, carbon and oxygen on a surface of the carbon support. The ratio of carbon atoms to oxygen atoms on the surface is at least about 20: 1, as measured by X-ray photoelectron spectroscopy. In another embodiment directed to the process for the preparation of N- (phosphonomethyl) glycine or a salt of the same, the catalyst comprises a carbon support having a noble metal on a surface of the carbon support. The carbon support also comprises a surface layer having a thickness of approximately 50 A, measured inward from the surface, and comprising carbon and oxygen. The ratio of carbon atoms to oxygen atoms in the surface layer is at least about 20: 1, as measured by X-ray photoelectron spectroscopy. In another embodiment directed to the process for the preparation of N- (phosphonomethyl) glycine or a salt thereof, the catalyst is prepared by a process comprising depositing a noble metal on a surface of a carbon support, and then heating the surface to a temperature of at least about 400 ° C. In another embodiment directed to the process for the preparation of N- (phosphonomethyl) glycine or a salt thereof, the catalyst is prepared by a process comprising depositing a noble metal on a surface of a carbon support and then exposing the surface to a reducing means. In this embodiment, before the deposition of noble metal, the carbon support has carbon and oxygen on its surface in quantities such that the ratio of carbon atoms to oxygen atoms on the surface is at least 20: 1, measured by x-ray photoelectron spectroscopy. In another embodiment directed to the process for the preparation of N- (phosphonomethyl) glycine or a salt thereof, the catalyst comprises a carbon support having a noble metal, a promoter and oxygen in a surface of the carbon support. In another embodiment directed to the process for the preparation of N- (phosphonomethyl) glycine or a salt thereof, the catalyst comprises a carbon support having a noble metal and a promoter on a surface of the carbon support. The catalyst also comprises a surface layer having a thickness of approximately 50 A, measured inward from the surface. This surface layer comprises carbon and oxygen. In this modality, the catalyst is characterized by having a ratio of carbon atoms to oxygen atoms in the surface layer that is at least about 20: 1, as measured by X-ray photoelectron spectroscopy after heating the catalyst to a temperature of about 500 ° C for about one hour in a hydrogen atmosphere, and before exposing the catalyst to an oxidant after heating in the hydrogen atmosphere. Other features of this invention will be partly evident and in part will be set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a TEM image of an oxidation catalyst comprising a carbon support having platinum alloyed with iron on the surface of the carbon support. Figure 2 is a high-energy X-ray spectrum of resolution, of a single metal particle, of an oxidation catalyst comprising a carbon support having platinum alloyed with iron on its surface.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES A.-The oxidation catalyst. The catalyst of the present invention can be used to catalyze oxidation reactions in liquid phase (ie, in aqueous solution or in an organic solvent), especially in acidic oxidative media and in the presence of solvents, reagents, intermediates or products that solubilize metals noble The catalyst exhibits significantly improved resistance to noble metal leaching under these conditions. Conveniently, the catalyst further exhibits improved oxidation (i.e., destruction) of the by-products of formaldehyde and formic acid during the oxidation of PMIDA to N- (phosphonomethyl) glycine.

The noble metal component of the catalyst serves several functions. For example, by depositing a noble metal on the surface of a catalyst consisting of a carbon-only support, the rate of deactivation of the catalyst tends to decrease. To illustrate, when N- (phosphonomethyl) glycine is prepared by oxidative decomposition in the liquid phase of PMIDA with oxygen in the presence of a catalyst consisting of an activated carbon support and a noble metal, it is found that the activated carbon is deactivated in 10% per cycle or more. Without wishing to be bound by any particular theory, it is believed that deactivation of the activated carbon arises because the surface of the carbon support is oxidized under the reaction conditions. See Chou, US patent. No. 4,624,937. See also, Chou, U.S. Pat. No. 4,696,772, which provides a separate discussion related to the deactivation of activated carbon by the oxidation of the carbon surface. In the presence of the noble metal, however, the deactivation rate of the activated carbon decreases. It is believed that the noble metal can react with the oxidant at a faster rate than the activated carbon surface and thus preferably removes the oxidant from the solution before extensive oxidation of the carbon surface can occur. In addition, unlike many oxide species that form on the surface of activated carbon and require high temperature treatments to be reduced, the oxide species that form on the surface of a noble metal are usually easily reduced. with the reducing agents present or added to the reaction mixture (for example, the separated fragment of amine, formaldehyde, formic acid, H2, etc.), thus restoring the noble metal surface to a reduced state. In this way, the catalyst of this invention advantageously exhibits a significantly longer life, while the noble metal is not lost by leaching or sintering (ie, in the form of inconveniently thick layers or clusters) by processes such as dissolution and redeposition or agglomeration of noble metal. Also, depending on the particular oxidation reaction, a noble metal may be more effective than carbon in effecting oxidation. For example, in the context of the oxidative decomposition of PMIDA to form N- (phosphonomethyl) glycine, although the carbon component of the catalyst mainly effects the oxidation of PMIDA to N- (phosphonomethyl) glycine, it is the noble metal component which it primarily effects the oxidation of the undesirable byproducts of formaldehyde and formic acid in the most preferred byproducts, carbon dioxide and water. It has been discovered, according to this invention, that oxygen-containing functional groups (e.g., carboxylic acids, ethers, alcohols, aldehydes, lactones, ketones, esters, amine oxides, and amides) on the surface of the carbon support, potentially increase the sintering of the noble metal during the oxidation reactions in liquid phase, and thus reduce the ability of the catalyst to oxidize oxidizable substrates, particularly formaldehyde, during the oxidation reaction of PMIDA. As used herein, an oxygen-containing functional group is "on the surface of the carbon support" if it is attached to a carbon support atom and is capable of chemically or physically interacting with compositions within the reaction mixture or with the metal atoms deposited on the carbon support. Many of the oxygen-containing functional groups that reduce the resistance of the noble metal to leaching and sintering and reduce catalyst activity are desorbed from the carbon support as carbon monoxide when the catalyst is heated to a high temperature (e.g., 900 ° C) in an inert atmosphere (for example, helium or argon). In this way, the measurement of the amount of CO desorption of a new catalyst (ie, a catalyst that has not been previously used in a liquid phase oxidation reaction) under high temperatures, is a method that can be used for analyze the surface of the catalyst and predict the noble metal retention and the conservation of catalyst activity. One way to measure CO desorption is using thermogravimetric analysis with in-line mass spectroscopy ("TGA-MS"). Preferably, no more than about 1.2 mmol of carbon monoxide per gram of catalyst is desorbed from the catalyst when a new, dry sample of the catalyst is subjected to a helium atmosphere at a temperature that increases from about 20 to about 900. ° C, at about 10 ° C per minute, and then kept constant at about 900 ° C for about 30 minutes.

Preferably, no more than about 0.7 mmol of carbon monoxide per gram of new catalyst is desorbed under such conditions; preferably no more than about 0.5 mmol of carbon monoxide per gram of new catalyst is desorbed, and no more than about 0.3 mmol of carbon monoxide per gram of new catalyst is very preferred. A catalyst is considered "dry" when it has a moisture content of less than about 1% by weight. Generally, a catalyst can be dried by placing it in a vacuum purged with N2 of about 63.5 cm Hg and a temperature of about 120 ° C, for about 16 hours. The measurement of the number of oxygen atoms on the surface of a new catalyst support is another method that can be used to analyze the catalyst and predict noble metal retention and maintenance of catalytic activity. Using for example X-ray photoelectron spectroscopy, a surface layer of the support that is approximately 50A thick is analyzed. The currently available equipment that is used for X-ray photoelectron spectroscopy generally has an accuracy within ± 20%. Typically, a ratio of carbon atoms to oxygen atoms on the surface is suitable (measured by the equipment currently available for photoelectron spectroscopy. X-ray), of at least about 20: 1 (carbon atoms: oxygen atoms). Preferably, however, the ratio is at least about 30: 1, preferably at least about 40: 1, preferably at least about 50: 1, and at least 60: 1 is most preferred. In addition, the ratio of oxygen atoms to metal atoms on the surface (again, measured by means of currently available equipment for X-ray photoelectron spectroscopy), is preferably less than about 8: 1 (oxygen atoms: metal atoms) preferably, the ratio is less than 7: 1, preferably less than about 6: 1, and less than about 5: 1 is most preferred. In general, the carbon supports used in the present invention are well known in the art. Non-graphitized activated carbon supports are preferred. These supports are characterized by a high adsorbent capacity for gases, vapors and colloidal solids, and by relatively high specific surface areas. Conveniently, the support can be a charcoal, charcoal or charcoal produced by means known in the art, for example, by destructive distillation of wood, peat, lignite, hard coal, walnut shells, bones, vegetables, or other carbonaceous material natural or synthetic, but preferably "activated" to develop the adsorbent power. Usually, activation is obtained by heating at high temperatures (800-900 ° C) with steam or carbon dioxide, which produces a porous particle structure and increases the specific surface area. In some cases, to increase the adsorptive capacity, hygroscopic substances such as zinc chloride and / or phosphoric acid or sodium sultafo are added before the destructive distillation or activation. Preferably, the carbon content of the carbon support varies from about 10% for bone carbon, to about 98% for some wood pellets and almost 100% for activated carbons derived from organic polymers. The non-carbonaceous matter in commercially available activated carbon materials normally varies depending on factors such as precursor origin, processing, and activation method. Many commercially available carbon supports contain small amounts of metals. Carbon supports having the least amount of oxygen-containing functional groups on their surfaces are preferred. The shape of the carbon support is not critical. In an embodiment of this invention, the support is a monolithic support. Suitable monolithic supports can have a wide variety of forms. For example, said support may be in the form of a grid or honeycomb. Also said support can be in the form of a reactor impeller. In a particularly preferred embodiment, the support is in the form of particles. As the particulate supports are especially preferred, most of the following description focuses on embodiments using a particulate support. It should be recognized, however, that this invention is not limited to the use of particulate supports. Suitable particulate supports can have a variety of shapes. For example, said supports may be in the form of granules. Preferably, the support is in powder form. These particulate supports can be used in a reactor system as free particles or, alternatively, they can be attached to a structure in the reactor system, such as a grid or impeller. Typically, a support that is in particulate form comprises a broad particle size distribution. For powders, preferably at least about 95% of the particles are from about 2 to about 300 m in their largest dimension, preferably at least about 98% of the particles are from about 2 to about 200 m in size. larger dimension, and it is highly preferred that about 99% of the particles are from about 2 to about 150 m in their largest dimension, with about 95% of the particles being from about 3 to about 100 m in their largest dimension . Particles that are larger than about 200 m in their largest dimension, tend to fracture into superfine particles (ie, less than 2 m in their largest dimension), which are difficult to recover. The specific surface area of the carbon support, measured by the BET method (Brunauer-Emmett-Teller) using N2, is preferably about 10 to about 3000 m2 / g (surface area of the carbon support per gram of carrier support). carbon), preferably from about 500 to about 2100 m2 / g, and from about 750 to about 2100 m2 / g is most preferred. In some embodiments, the preferred specific area is from about 750 to about 1750 m2 / g.

The pore volume of the support can vary widely. Using the measurement method described in example 1, the pore volume is preferably from 0.1 to about 2.5 ml / g (pore volume per gram of catalyst), preferably from about 0.2 to about 2.0 ml / g, and preferably from about 0.4 to about 1.7 ml / g. Catalysts comprising supports with pore volumes greater than about 2.5 ml / g, tend to fracture easily. On the other hand, catalysts comprising supports having pore volumes of less than 0.1 ml / g, tend to have small surface areas and therefore low activity. The carbon supports for use in the present invention are commercially available from various sources. The following is a list of some of the activated carbons that can be used with this invention: Darco G-60 Spec and Darco X (ICI-America, Wilmington, DE), Norit SG Extra, Norit EN4, Norit EXW, Norit A, Norit Ultra-C, Norit ACX, and Norit Mesh 4 x 14 (Amer. Norit Co., Inc., Jacksonville, FL); GI-9615, VG-8408, VG-8590, NB-9377, XZ, NW and JV (Bamebey-Cheney, Columbus, OH); BL Pulv., PWA Pulv., Calgon C 450, and PCB Fines (Pittsburgh Activated Carbon, Div. Calgon Corporation, Pittsburgh, PA); P-100 (No. Amer. Carbon, Inc., Columbus, OH); Nuchar CN, Nuchar C-100 N, Nuchar C-190 A, Nuchar C-115 A, and Nuchar SA-30 (Westvaco Corp., Coal Department, Covington, Virginia); Code 1551 (Baker and Adamson, Division of Allied Amer. Norit Co., Inc., Jacksonville, FL); Grade 235, Grade 337, Grade 517 and Grade 256 (Witco Chemical Corp., Activated Carbon Div., New York, NY); and Columbia SXAC (Union Carbide New York, NY). The catalyst of this invention preferably has one or more noble metals on its surface. Preferably, the noble metal is selected from the group consisting of platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium (Ir), silver (Ag), osmium (Os) and gold (Au) ). In general, platinum and palladium are preferred, with platinum being most preferred. Since platinum is currently the preferred noble metal, the following description is directed primarily to platinum-using modalities. It should be understood, however, that the same description is applicable in general to the other noble metals and combinations thereof. It should also be understood that the term "noble metal" as used herein, means that the noble metal is in its elemental state, as well as the noble metal in any of its different oxidation states. The concentration of the noble metal deposited on the surface of the carbon support can vary within wide limits. Preferably, it is on the scale of from about 0.5 to about 20% by weight ([mass of noble metal - total mass of catalyst] x 100%), preferably from about 2.5 to about 10% by weight, and is most preferred from about 3 to about 7.5% by weight. If concentrations lower than 0.5% by weight are used during the oxidation reaction of PMIDA, the aldehyde tends to be less oxidized, and therefore a greater amount of NMG is produced, thus reducing the yield of N- (phosphonomethyl) glycine. On the other hand, at concentrations greater than about 20% by weight, layers and clusters of noble metal tend to form. In this way, there are fewer noble metal atoms on the surface per total amount of noble metal used. This tends to reduce the activity of the catalyst and is a non-economic use of the expensive noble metal. The dispersion of the noble metal on the surface of the carbon support is such that preferably the concentration of noble metal atoms on the surface is from about 10 to about 400 μmoles / g (μmoles of noble metal atoms of surface per gram of catalyst), preferably from about 10 to about 150 μmol / g, and from about 15 to about 100 μmol / g is most preferred. This can be determined, for example, by measuring the chemosorption of H2 or CO using a Altamira AMI100 (Zeton Altamira, Pittsburg, PA). Preferably, the noble metal is on the surface of the carbon support in the form of metal particles. At least about 90% (numerical density) of the noble metal particles on the surface of the carbon support are from about 0.5 to about 35 nm in their largest dimension, preferably from about 1 to about 20 nm in their largest dimension large, and is most preferred from about 1.5 to about 10 nm in its largest dimension. In a particularly preferred embodiment, at least about 80% of the noble metal particles on the surface of the carbon support are from about 1 to about 15 nm in their largest dimension, preferably from about 1.5 to about 10 nm in their larger dimension, and is most preferred from about 1.5 to about 7 nm in its largest dimension. If the noble metal particles are too small, there tends to be an increased amount of leaching when the catalyst is used in a medium which tends to solubilize noble metals, as is the case when PMIDA is oxidized to form N- (phosphonomethyl) glycine. On the other hand, as the particle size increases, there tend to be fewer noble metal surface atoms per total amount of noble metal used. As described above, this tends to reduce catalyst activity and is also a non-economic use of the expensive noble metal. In addition to the noble metal, at least one promoter may be present on the surface of the carbon support. Although typically the promoter is deposited on the surface of the carbon support, other sources of promoter can be used (for example, the carbon support itself can contain a promoter naturally). A promoter tends to increase the selectivity, activity and / or stability of the catalyst. In addition, a promoter can reduce the leaching of the noble metal. For example, the promoter can be a noble metal (or noble metals) on the surface of the carbon support. For example, it has been found that ruthenium and palladium act as promoters on a catalyst comprising platinum deposited on a carbon bearing surface. Alternatively, the promoter can be for example a metal selected from the group consisting of: tin (Sn), cadmium (Cd), magnesium (Mg), manganese (Mn), nickel (Ni), aluminum (Al), cobalt (Co) ), bismuth (Bi), lead (Pb), titanium (Ti), antimony (Sb), selenium (Se), iron (Fe), rhenium (Re), zinc (Zn), cerium (Ce) and zirconium (Zr) ). Preferably, the promoter is selected from the group consisting of bismuth, iron, tin and titanium. In a particularly preferred embodiment, the promoter is tin. In another particularly preferred embodiment, it is the iron. In a further preferred embodiment, the promoter is titanium. In a further preferred embodiment, the catalyst comprises both iron and tin. In general, the use of iron, tin, or both, (1) reduces the leaching of noble metal in a catalyst used over several cycles, (2) tends to increase and / or maintain the activity of the catalyst when it is used for effect the oxidation of PMIDA. Generally, ferrous-containing catalysts are preferred because they tend to have the highest activity and stability with respect to the oxidation of formaldehyde and formic acid. In a preferred embodiment, the promoter is oxidized more easily than the noble metal. A promoter is "more easily oxidized" if it has a lower ionization potential than the noble metal. The first ionization potentials for the elements are widely known in the art and can be found, for example, in the manual "CRC Handbook of Chemistry and Physics" -Manual of Chemistry and Physics CRC- (CRC Press, Inc., Boca Raton , Florida).

The amount of promoter on the surface of the carbon support (associated with the same carbon surface, metal, or a combination thereof), can vary within wide limits, depending, for example, on the noble metal and promoter used. Typically, the percentage by weight of the promoter is at least about 0.05% ([mass of promoter -? - total mass of the catalyst] x 100%). The percentage by weight of the promoter is preferably from about 0.05 to about 10%, preferably from about 0.1 to about 10%, preferably from about 0.1 to about 2%, and from about 0.2 to about 1.5% is most preferred. When the promoter is tin, the preferred weight percentage is from about 0.5 to about 1.5%. Promoter weight percentages less than 0.5% usually do not promote catalyst activity over a prolonged period. On the other hand, percentages by weight greater than about 10%, tend to decrease the activity of the catalyst. Also, the molar ratio of noble metal to promoter can vary widely, depending for example on the noble metal and promoter used. Preferably, the ratio is from about 1000: 1 to about 0.01: 1, preferably from about 150: 1 to about 0.05: 1, preferably from about 50: 1 to about 0.05: 1, and about 10 is most preferred. : 1 to approximately 0.05: 1. For example, a catalyst containing platinum and iron preferably has a molar ratio of platinum to iron of about 3: 1. In a particularly preferred embodiment of this invention, the noble metal (e.g., platinum) is alloyed with at least one promoter (e.g., tin, iron, or both) to form alloyed metal particles. A catalyst comprising a noble metal, alloyed with at least one promoter, tends to have all the advantages mentioned above with respect to catalysts comprising a promoter. However, it has been found that in accordance with this invention, catalysts comprising a noble metal, alloyed with at least one promoter, tend to exhibit greater resistance to leaching of the promoter and additional stability from cycle to cycle with respect to the oxidation of formaldehyde and formic acid. See example 17. The term "alloy" encompasses any metal particle comprising a noble metal and at least one promoter, regardless of the precise manner in which the noble metal and promoter atoms are disposed within the particle (although it is generally preferred to have a portion of the noble metal atoms on the surface of the alloyed metal particle). The alloy can be, for example, any of the following: 1. - An intermetallic compound An intermetallic compound is a compound comprising a noble metal and a promoter (e.g., Pt3Sn). 2. - A substitutional alloy A substitutional alloy has a single continuous phase, regardless of the concentrations of the noble metal atoms and the promoter. Typically, a substitutional alloy contains noble metal and promoter atoms that are of similar size (e.g., platinum and silver, or platinum and palladium). Substitutional alloys are also referred to as "monophasic alloys". 3. - A multiphasic alloy A multiphasic alloy is an alloy that contains at least two discrete phases. Said alloy may contain for example Pt3Sn in one phase, and tin dissolved in platinum in a separate phase. 4. - A segregated alloy A segregated alloy is a metal particle in which the stoichiometry of the particle varies with the distance from the surface of the metal particle.

. - An interstitial alloy An interstitial alloy is a metal particle where the noble metal atoms and the promoter combine with non-metallic atoms such as boron, carbon, silicon, nitrogen, phosphorus, etc.

Preferably, at least about 80% (numerical density) of the alloyed metal particles are from about 0.5 to about 35 nm in their largest dimension, preferably about 1 to about 20 nm in their largest dimension, preferably from about 1 to about 15 nm in its largest dimension, and preferably from about 1.5 to about 7 nm in its largest dimension. The alloyed metal particles do not require to have uniform composition; the compositions may vary from particle to particle, or even within the same particles. In addition, the catalyst may comprise particles consisting of the noble metal alone or the promoter alone. However, it is preferred that the composition of metal particles be substantially uniform from particle to particle and within each particle, and that the number of noble metal atoms in intimate contact with the promoter atoms, be the maximum. It is also preferred, although not essential, that most of the noble metal atoms are alloyed with a promoter, and it is highly preferred that substantially all noble metal atoms are alloyed with a promoter. It is also preferred, although not essential, that the alloyed metal particles are evenly distributed on the surface of the carbon support. Regardless of whether the promoter is alloyed with the noble metal, it is currently believed that the promoter tends to oxidize if the catalyst is exposed to an oxidant for a certain period. For example, an elemental tin promoter tends to oxidize to form Sn (ll) 0, and Sn (ll) 0 tends to oxidize to form Sn (IV) 02. This oxidation can occur for example if the catalyst is exposed to the air for more than about an hour. Although it has not been observed that said oxidation of the promoter has a significantly harmful effect on noble metal leaching, sintering of noble metal, catalyst activity or catalyst stability, it becomes more difficult to carry out the analysis of the concentration of groups. harmful fungi that contain oxygen on the surface of the carbon support. For example, as mentioned above, the concentration of harmful oxygen-containing functional groups (ie, oxygen-containing functional groups that decrease the leaching and sintering resistance of the noble metal and decrease catalyst activity) can be determined by measuring the amount of CO that is desorbed from the catalyst under high temperatures in an inert atmosphere (using for example TGA-MS). However, it is currently believed that when an oxidized promoter is present on the surface, the oxygen atoms of the oxidized promoter tend to react with carbon atoms of the support at high temperatures in an inert atmosphere to produce CO, thus creating the illusion of more harmful functional groups that contain oxygen on the surface of the support, of those that actually exist. Such oxygen atoms of an oxidized promoter can also interfere with obtaining a reliable prediction of noble metal leaching, noble metal sintering and catalyst activity, from simple measurement (for example by means of X-ray photoelectron spectroscopy) of oxygen atoms on the surface of the catalyst. In this way, when the catalyst comprises at least one promoter that has been exposed to an oxidant and has thus been oxidized (for example, when the catalyst has been exposed to air for more than about 1 hour), it is preferred that the The first promoter is substantially reduced (thus removing the oxygen atoms of the oxidized promoter from the catalyst surface), before attempting to measure the amount of harmful oxygen-containing functional groups on the surface of the carbon support. This reduction is preferably obtained by heating the catalyst at a temperature of about 500 ° C for about 1 hour, in an atmosphere consisting essentially of H2. The measurement of harmful functional groups containing oxygen on the surface is preferably effected: (a) after this reduction, and (b) before exposing the surface to an oxidant after reduction. Preferably, the measurement is taken immediately after the reduction. The preferred concentration of metal particles on the surface of the carbon support depends, for example, on the size of the metal particles, the specific surface area of the carbon support, and the concentration of noble metal on the catalyst. It is currently believed that, in general, the preferred concentration of metal particles is from about 3 to about 1, 500 particles / μm 2 (i.e., number of metal particles per μm 2 of carbon bearing surface), particularly where: ( a) at least about 80% (numerical density) of the metal particles are from about 1.5 to about 7 nm in their largest dimension, (b) the carbon support has a specific surface area of from about 750 to about 2100 m2 / g (ie, m2 of carbon support surface per gram of carbon support), and (c) the concentration of noble metal on the surface of the carbon support is from about 1 to about 10% by weight ([ noble metal mass - total catalyst mass] x 100%). In highly preferred embodiments, narrower scales of metal particle concentrations and noble metal concentrations are sought. In one such embodiment, the concentration of the metal particles is from about 15 to about 800 particles / μm 2, and the concentration of noble metal on the surface of the carbon support is from about 2 to about 10% by weight. In a highly preferred embodiment, the concentration of metal particles is from about 15 to about 600 particles / μm 2, and the concentration of noble metal at the surface of the carbon support is from about 2 to about 7.5% by weight. In the most preferred embodiment, the concentration of the metal particles is from about 15 to about 400 particles / μm 2, and the concentration of noble metal on the surface of the carbon support is about 5% by weight. The concentration of the metal particles on the surface of the carbon support can be measured using methods known in the art.

(B) Process for the preparation of the oxidation catalyst 1. Deoxygenation of the carbon support Preferably, the surface of the carbon support is deoxygenated before depositing the noble metal thereon. Preferably, the surface is deoxygenated using a high temperature deoxygenation treatment. Said treatment may be a single step or a multi-step program which, in any case, results in a general chemical reduction of the oxygen-containing functional groups on the surface of the carbon support. In a two-step deoxygenation treatment at high temperature, preferably the carbon support is first treated with a gaseous or liquid phase oxidizing agent to convert the oxygen-containing functionalities into relatively lower oxidation states (eg, ketones, aldehydes and alcohols), in functionalities in relatively higher oxidation states (eg carboxylic acids), which are easier to separate from the catalyst surface at high temperatures. Representative liquid phase oxidizing agents include nitric acid, H2O2, chromic acid and hypochlorite, concentrated nitric acid consisting of about 10 to about 80 grams of HN03 per 100 grams of aqueous solution being preferred. Representative gaseous oxidants include molecular oxygen, ozone, nitrogen dioxide and nitric acid vapors. Nitric acid vapors are the preferred oxidizing agent.

With a liquid oxidant, temperatures of about 60 to about 90 ° C are appropriate, but with gaseous oxidants, it is often advantageous to use temperatures of about 50 to about 500 ° C, or even higher. The time during which the carbon is treated with the oxidant can vary widely from about 5 minutes to about 10 hours. Preferably, the reaction time is from about 30 minutes to about 6 hours. The experimental results indicate that the carbon load, the temperature, the oxidant concentration, etc. in the first step of the treatment, they are not strictly critical to obtain the desired oxidation of the carbon material, and thus can be handled at convenience over a wide range. For economic reasons, the highest possible carbon load is preferred. In the second step, the oxidized carbon support is pyrolyzed (ie, heated) to a temperature preferably in the range from about 500 to about 1500 ° C, and preferably from about 600 to about 1,200 ° C, in a nitrogen, argon, helium or other non-oxidizing medium (that is, a medium that essentially does not contain oxygen), to remove oxygen-containing functional groups from the carbon surface. At temperatures greater than 500 ° C, a medium can be used that comprises a small amount of ammonia (or any other chemical entity that generates NH3 during pyrolysis), steam or carbon dioxide that aids in pyrolysis. As the carbon support cools at temperatures below 500 ° C, however, the presence of oxygen-containing gases such as steam or carbon dioxide can lead to the new formation of surface oxides and therefore should be avoided. . Consequently, the pyrolysis is preferably carried out in a non-oxidizing atmosphere (for example, nitrogen, argon or helium). In one embodiment, the non-oxidizing atmosphere comprises ammonia, which tends to produce a more active catalyst in a shorter time compared to pyrolysis in the other atmospheres. The pyrolysis can be carried out, for example, using a rotating kettle, a fluidized bed reactor, or a conventional oven. The carbon support is generally pyrolyzed for a period of from about 5 minutes to about 60 hours, preferably from about 10 minutes to about 6 hours. Shorter times are preferred because prolonged carbon exposure at elevated temperatures tends to reduce catalyst activity. Without linking to any particular theory, it is currently believed that prolonged heating at pyrolytic temperatures favors the formation of graphite, which is a less preferred form of carbon support because it usually has less surface area. As mentioned above, a more active catalyst can generally be produced in a shorter time using an atmosphere comprising ammonia. In a preferred embodiment of this invention, deoxygenation at high temperature is carried out in one step. This one-step treatment may only consist of carrying out the pyrolysis step of the two-step high-temperature deoxygenation treatment mentioned above. Preferably, however, the one-step treatment consists of pyrolysis of the carbon support as described above, while simultaneously passing over the coal a gas stream comprising N2, NH3 (or any other chemical entity that generates NH3 during pyrolysis) and steam. Although not a critical feature of this invention, the flow velocity of the gas stream is preferably fast enough to achieve adequate contact between the new gas reactants and the carbon surface, but sufficiently low to avoid excess loss of gas. carbon weight and waste of material. A non-reactive gas can be used as a diluent to avoid severe loss of carbon weight. 2. Deposition of noble metal (s) Generally, the methods used to deposit the noble metal on the surface of the carbon support are known in the art, and include liquid phase methods such as reaction deposition techniques (e.g. deposition by reduction of noble metal compounds, and deposition by hydrolysis of noble metal compounds), ion exchange techniques, impregnation in excess of solution, and incipient impregnation of moisture; vapor phase methods such as physical deposition and chemical deposition; precipitation; electrochemical deposition; and non-electrolytic deposition. See in general, Cameron DS, Cooper SJ, Dodgson IL, Harrison B., and Jenkins JW, "Carbons and Supports for Precious Metal Catalysts" -Carbonds and supports for precious metal catalysts- Catalysts Today, 7, 113-137 (1990 ). Catalysts comprising noble metals are also commercially available on the surface of a carbon support, for example 5% platinum on activated carbon, Aldrich Catalog No. 20,593-1, and 5% palladium on activated carbon, Aldrich Catalog. No. 20,568-0 (Aldrich Chemical Co., Inc., Milwaukee, Wisconsin). Preferably, the noble metal is deposited by means of a reactive deposition technique comprising contacting the carbon support with a solution comprising a salt of the noble metal, and then hydrolyzing the salt. An example of a suitable platinum salt that is relatively inexpensive is hexachloroplatinic acid (H2PtCl6). Example 3 illustrates the use of this salt to deposit platinum on a carbon support by means of hydrolytic deposition. In one embodiment of this invention, the noble metal is deposited on the surface of the carbon support using a solution comprising a salt of a noble metal in one of its most reduced oxidation states. For example, instead of using a salt of Pt (IV) (for example, H2PtCI6), a salt of Pt (ll) is used. In another embodiment, platinum is used in its elemental state (eg, colloidal platinum). The use of these smaller metal precursors leads to less oxidation of the carbon support and, therefore, fewer oxygen-containing functional groups are formed on the surface of the support, while the noble metal is deposited on the surface. An example of a salt of Pt (ll) is K2PtCl4. Another potentially useful Pt (ll) salt is platinum (II) diaminodinitrite. Example 11 shows that the use of this salt to deposit the noble metal produces a catalyst that is more resistant to leaching than a catalyst prepared using H2PtCl6 as a metal precursor. Without being bound by any particular theory, it is believed that this is due to the fact that platinum (II) diaminodinitrite generates ammonia in situ during the reaction, which subsequently promotes the removal of oxygen-containing functional groups on the surface of the carbon support. However, this benefit must be weighed against a possible explosion hazard associated with the use of platinum (II) diaminodinitrite. 3. Deposition of the promoter (s) A promoter (or promoters) can be deposited on the surface of the carbon support, before, simultaneously with, or after, the deposition of the noble metal on the surface. In general, the methods used to deposit a promoter on the surface of the carbon support are known in the art, and include the same methods used to deposit the noble metal mentioned above. In one embodiment, to deposit the promoter, a salt solution comprising the promoter is used. A suitable salt that can be used to deposit bismuth is Bi (N? 3) 3 »5H2 ?, a suitable salt that can be used to deposit iron is FeCI3 * 6H2O, and a suitable salt that can be used to deposit tin is SnCl2 »2H2O. It should be recognized that more than one promoter can be deposited on the surface of the carbon support. The examples 13, 14, 15 and 17 demonstrate the deposition of a promoter on a carbon surface with a salt solution comprising a promoter. Example 18 demonstrates the deposition of more than one promoter (ie, iron and Sn) on a carbon surface using salt solutions comprising the promoters. As indicated above, a catalyst comprising a noble metal in alloy with at least one promoter is particularly preferred. There is a variety of possible preparative techniques known in the art that can be used to form a multimetal alloy on the surfaces of the support. See for example V. Ponec and G.C. Bond, "Catalysts by Metals and Alloys", -Catalyst by means of metals and alloys- in "Studies on Surface Science and Catalysis" -Studies in the Science of surfaces and catalysts- Vol. 95 (B. Delmon and JT Yates , consulting editors, Elsevier Science BV, Amsterdam, The Netherlands). In one of the most preferred embodiments, reactive deposition is used to form metal particles containing a noble metal alloyed with a promoter. The reactive deposition may comprise, for example, reductive deposition in which a surface of a carbon support is contacted with a solution comprising: (a) a reducing agent; and (b) (i) a compound comprising the noble metal and a compound comprising the promoter, or (ii) a compound comprising both the noble metal and the promoter. A wide variety of reducing agents can be used such as for example sodium borohydride, formaldehyde, formic acid, sodium formate, hydrazine hydrochloride, hydroxylamine and hypophosphorous acid. Compounds comprising a noble metal and / or a promoter include, for example: 1. - Halide compounds These include, for example, H2PtCI6, K2PtCI4, Pt2Br62", K2PdCI4, AuCI41", RuCI3, RhCl3"3H2O, K2RuCI6, FeCl3" 6H20, (SnCl3) 1-, SnCl4, ReCI6, FeCI2 and T¡CI4. 2. - Oxide and oxychloride compounds These include, for example, RuO42"and M2SnO4. 3. - Nitrate compounds These include, for example, Fe (N03) 34. - Amine complexes These include, for example, [Pt (NH3) 4] CI2, [Pd (NH3) 4] CI2, Pt (NH3) 2CI2) [Pt (NH3) 4] PtCl4) Pd (NH2CH2CH2NH2) Cl2, PtíNhfeChfeChfeNhfekCk , and [Ru (NH3) 5CI] CI2.

. - Phosphine complexes These include, for example, Pt (P (CH3) 3) 2Cl2, lRCOCO (P (C6H5) 3) 2, PtClH (PR3) 2, wherein each R is independently a hydrocarbyl such as methyl, ethyl, propyl, phenyl, etc. 6. - Organometallic complexes These include, for example, Pt ^ CsH? ^ CU, Pc ^^^ CU, Pt (CH3COO) 2, Pd (CH3COO) 2, K [Sn (HCOO) 3], Fe (CO) 5, Fe3 (CO) 12, Fe 4 (CO) 16, Sn 3 (CH 3) 4 and Ti (OR) 4, wherein each R is independently a hydrocarbyl such as methyl, ethyl, propyl, phenyl, etc. 7. - Noble metal / promoter complexes These include, for example, Pt3 (SnCl3) 2 (C8Hi2) 3 and [Pt (SnCl3) 5] 3 \ In a particularly preferred embodiment, hydrolysis reactions are used to deposit a noble metal alloyed with a promoter. In this case, ligands containing the noble metal and the promoter are formed, and then hydrolyzed to form well-mixed clusters of metal oxide and metal hydroxide on the surface of the carbon support. The ligands can be formed, for example, by contacting the surface of the support with a solution comprising (a) a compound comprising the noble metal and a compound comprising the promoter, or (b) a compound comprising both the noble metal as the promoter. Suitable compounds comprising a noble metal and / or a promoter are mentioned above with respect to reductive deposition. The hydrolysis of the ligands can be achieved, for example, by heating the mixture (for example, at a temperature of at least about 60 ° C). Example 17 further demonstrates the use of hydrolysis reactions to deposit a noble metal (ie, platinum) alloyed with a promoter (ie, iron). In addition to the above-mentioned reactive deposition techniques, there are many other techniques that can be used to form the alloy. These include, for example: 1.- Forming the alloy by introducing metal compounds (which may be simple or complex, and which may be covalent or ionic) on the surface of the support by impregnation, adsorption of a solution and / or ion exchange. . 2.- Form the alloy by vacuum co-deposition of metal vapors containing the noble metal and the promoter on the surface. 3.- Form the alloy by depositing one or more metals on a predeposited metal that belongs to group 8, 9 or 10 of the Periodic Table of the Elements (ie, Fe, Co, Ni, Ru, Rh, Pd, Os, Go and Pt) by, for example, electrolytic or non-electrolytic coating. 4.- Form the alloy: (a) depositing metal complexes containing metals in the zero-valent state (eg, carbonyl, p / -alyl, or cyclopentadienyl complexes of the noble metal and the promoter) on the surface of the support of carbon; and (b) removing the ligands, for example by means of heating or reduction to form the alloy particles on the surface. 5.- Forming the alloy by contacting a solution containing a metal compound (for example, a metal chloride or a metal alkyl compound) with a predefined metal hydride containing a metal of group 8, 9 or 10 of The periodic table. 6.- Form the alloy by co-depositing, either simultaneously or sequentially, metal complexes (preformed or formed in situ) containing the noble metal (or metals) and the promoter (s) on the surface of the support of carbon. 7.- Form the alloy by preforming particles of the alloy as colloids or aerosols, and then depositing the preformed alloy particles on the surface of the carbon support. To illustrate, colloidal particles containing platinum and iron can be easily formed by boiling a dilute solution of H2PtCl6 and SnCl2 «2H20 with a solution of sodium citrate. Protective agents (eg, carbohydrates, polymers, lipophilic nitrogen quaternary salts) can be used to effectively control the growth of the metal alloy particles. This technique, therefore, is often useful to form a reduced distribution of the particle sizes of the alloy. It should be recognized that the techniques mentioned above for forming an alloy are merely illustrative and not exhaustive. Using the teachings of this specification and the general knowledge of the art, any person of average skill in the art can routinely determine which of the many alloy preparation techniques known in the art to be suitable for a particular use. Regardless of the technique used to form the alloy, after having deposited the metals on the surface of the carbon support, it is often preferable to dry the support using for example a non-oxidizing subatomic medium (preferably N2) a noble gas or both). A drying step is particularly preferred when the surface of the support is to be subsequently reduced by heating the surface (and it is even more preferable when the heating is performed in a non-oxidizing medium). Preferably, the support is dried to decrease the moisture content to less than about 5% by weight. It should be recognized that by reducing the surface of the carbon support after the deposition of the noble metal (or metals) and the promoter (s), the extension of alloyed noble metal with a promoter typically increases. Said reduction often also tends to increase the number of particles within the preferred scale of size. 4. Reduction of the surface of the carbon support After having impregnated the carbon support with the noble metal (s) (and promoter or promoters, if applicable), the surface of the catalyst is preferably reduced. The surface of the catalyst can be adequately reduced, for example, by heating the surface to a temperature of at least about 400 ° C. It is especially preferable to carry out this heating in a non-oxidizing medium (for example, nitrogen, argon or helium). It is also preferred that the temperature be greater than about 500 ° C. Preferably, the temperature is from about 550 to about 1, 200 ° C, and from about 550 to about 900 ° C is most preferred. Temperatures below 400 ° C tend to be unsatisfactory to remove the oxygen-containing functional groups from the surface of the carbon support. On the other hand, temperatures higher than 1, 200 ° C tend to decrease the activity of the catalyst. Preferably temperatures of about 400 to about 500 ° C are used, only if the surface of the carbon support has a ratio of carbon atoms to oxygen atoms of at least about 20: 1 before depositing the noble metal on the surface. In a particularly preferred embodiment, the catalyst surface is reduced by a method comprising exposing the surface to a reducing medium. For example, before heating, the catalyst sample can be pretreated with a liquid phase reducing agent such as formaldehyde or formic acid. Preferably, the heating is carried out in the presence of a gaseous phase reducing agent (the method of heating the catalyst in the presence of a gas phase reducing agent will sometimes be referred to as "gas phase reduction at a high temperature"). Various gaseous phase reducing agents can be used during heating, including but not limited to, H2, ammonia and carbon monoxide. Hydrogen gas is the most preferred since the small molecular size of hydrogen allows better penetration into the deeper pores of the carbon support. Preferably, the remainder of the gas consists essentially of a non-oxidizing gas such as nitrogen, argon or helium. The gas can comprise any finite concentration of H2, although H2 concentrations of less than 1.0% are inconvenient, due to the time they usually require to reduce the surface of the support. Preferably, the gas comprises about 5 to about 50 volume% H, and most preferably about 5 to about 25 volume% H2. The preferred amount of time that the catalyst surface is heated depends on the mass transfer of the reducing agent to the surface of the catalyst. When the reducing agent is a non-oxidizing gas comprising about 10 to about 20 volume% H2, preferably the surface is heated for about 15 minutes to about 24 hours, at a temperature of about 550 to about 900 ° C, with a space velocity of about 1 to about 5,000 hours. "1 Preferably, the space velocity is about 10 to about 2,500 hours" 1, and from about 50 to about 750 hours is most preferred "1. most preferred, the heat treatment is carried out at the above preferred temperatures and at space speeds of about 1 to about 10 hours.It is not convenient to heat the surface at space speeds of less than 1 hour "1, since it can happen that functional groups containing oxygen on the surface of the carbon support are not sufficiently destroyed. On the other hand, the heating of the surface at space speeds greater than 5,000 hours is not economical. "1 In accordance with this invention, it has been found that the pre-existing oxygen-containing functional groups on the surface of the carbon support are neither necessary nor desired, to obtain adequate dispersion and retention of noble metal. Without being bound by any particular theory, it is believed that this heating step increases the platinum-carbon interaction on the catalyst, removing oxygen-containing functional groups on the surface of the carbon support, including those formed by depositing the noble metal on the surface. It is believed that these oxygen-containing functional groups are unstable anchoring sites for the noble metal, since they tend to interfere with the potentially stronger interactions between the noble metal and the carbon support. The single heating will decompose, and therefore remove, many of the functional groups that contain oxygen on the surface of the carbon support. However, by heating the surface in the presence of a reducing agent (eg, H2), more oxygen-containing functional groups will be susceptible to being eliminated.

If the ratio of carbon atoms to oxygen atoms on the surface of the carbon support is less than about 20: 1 before depositing the noble metal on the surface of the support, the surface is preferably reduced using the gas phase reduction treatment. at high temperature mentioned above, at a temperature higher than 500 ° C, although the surface can optionally be treated with other reduction means in addition to the reduction in gas phase at high temperature. On the other hand, if the surface of the carbon support has a ratio of carbon atoms to oxygen atoms that is at least about 20: 1 before the noble metal is deposited on the surface, various media can be used. alternative reduction instead of reduction in gas phase at high temperature. The surface of the catalyst can be reduced, at least in part, by treating it with an amine such as for example urea, a solution comprising ammonium ions (for example, ammonium formate or ammonium oxalate), or ammonia gas, with Ammonia gas or a solution that includes ammonium ions. This amine treatment is preferably used in addition to other reduction treatments, and most preferably it is used before the gas phase reduction at high temperature. In one such embodiment, the noble metal is deposited on the surface by treating it with a noble metal precursor solution comprising ammonium ions. Alternatively, after depositing the noble metal on the surface of the support, it can be washed with a solution comprising ammonium ions or it can be contacted with a gas comprising ammonia. Preferably, the catalyst surface is washed with dilute aqueous ammonia after depositing the noble metal. In this case, the catalyst is added to pure water and stirred for a few hours to wet the surface of the catalyst. Then, while continuing to stir the catalyst slurry, a solution comprising ammonium ions in an amount sufficient to produce a pH greater than 7, preferably from about 8 to about 12, is added to the catalyst slurry, and is most preferred to approximately 9.5 to approximately 11.0. Since the temperature and pressure are not critical, this step is preferably carried out at room temperature and atmospheric pressure. Example 10 further demonstrates this reduction treatment. Sodium borohydride (NaBH4) can also be used to reduce the surface area of the catalyst. As with the amine treatment, this treatment is preferably used in addition to other reduction treatments, and most preferably it is used before the gas phase reduction at high temperature. Preferably, after depositing the noble metal on the surface of the support, the support is washed with a solution of NaBH 4 in the presence of NaOH at a pH of about 8 to about 14 for about 15 to about 180 minutes. The amount of NaBH 4 used is preferably sufficient to reduce all the noble metal. Since the temperature and pressure are not critical, this step is preferably carried out at room temperature and atmospheric pressure. Example 12 further demonstrates this reduction treatment. It should be recognized that any of the above treatments that can be used to reduce the surface of the catalyst can also be used to deoxygenate the surface of the carbon support before the noble metal is deposited on the surface.

C. Use of the oxidation catalyst The catalyst described above can be used for liquid phase oxidation reactions. Examples of such reactions include the oxidation of alcohols and polyols to form aldehydes, ketones and acids (for example, the oxidation of 2-propanol to form acetone, and the oxidation of glycerol to form glyceraldehyde, dihydroxyacetone or glyceric acid); the oxidation of aldehydes to form acids (for example, the oxidation of formaldehyde to form formic acid, and the oxidation of furfural to form 2-furancarboxylic acid); the oxidation of tertiary amines to form secondary amines (for example, the oxidation of nitrilotriacetic acid "NTA" to form iminodiacetic acid "IDA"); the oxidation of secondary amines to form primary amines (for example, the oxidation of IDA to form glycine); and the oxidation of various acids (eg, formic acid or acetic acid) to form carbon dioxide and water. The catalyst described above is especially useful in liquid phase oxidation reactions at pH levels less than 7, and in particular, at pH levels of less than 3. It is also especially useful in the presence of solvents, reagents, intermediates or products that solubilize noble metals. One such reaction is the oxidation of PMIDA or a salt thereof to form N- (phosphonomethyl) glycine, or a salt thereof, in a medium having pH levels in the range of about 1 to about 2. The following description will set forth in particular the use of the aforementioned catalyst to effect the oxidative decomposition of PMIDA or a salt thereof, to form N- (phosphonomethyl) glycine or a salt thereof. It should be recognized, however, that the principles discussed below are applicable in general to other oxidative reactions in liquid phase, especially those at pH levels below 7 and those that include solvents, reagents, intermediates or products that solubilize metals noble To start the oxidation reaction of PMIDA, it is preferable to charge the reactor with the PMIDA reagent (ie, PMIDA or one of its salts), catalyst, and a solvent, in the presence of oxygen. Most preferably, the solvent is water, although other solvents (for example glacial acetic acid) are also suitable. The reaction can be carried out in a wide variety of intermittent, semi-intermittent and continuous reactor systems. The configuration of the reactor is not critical. Suitable conventional reactor configurations include, for example, stirred tank reactors, fixed bed reactors, drip bed reactors, fluidized bed reactors, bubble flow reactors, fill flow reactors and parallel flow reactors. When the reaction is carried out in a continuous reactor system, the residence time in the reaction zone can vary widely depending on the specific catalyst and the conditions employed. Typically, the residence time may vary on the scale from about 3 to about 120 minutes. Preferably, the residence time is from about 5 to about 90 minutes, and preferably from about 5 to about 60 minutes. When performed in a charge reactor, the reaction time typically varies on the scale of about 15 to about 120 minutes. Preferably, the reaction time is from about 20 to about 90 minutes, and from about 30 to about 60 minutes is most preferred. In a broad sense, the oxidation reaction can be practiced in accordance with the present invention over a wide range of temperatures, and at pressures ranging from a subatmospheric pressure to a superatmospheric pressure. The use of mild conditions (for example, ambient temperature and atmospheric pressure) has obvious commercial advantages, since less expensive equipment can be used. However, by operating at higher temperatures and superatmospheric pressures, although the plant costs are increased, it tends to improve the phase transfer between the liquid and gas phase, and to increase the rate of oxidation of PMIDA. Preferably, the reaction of the PMIDA is carried out at a temperature of from about 20 to about 180 ° C, preferably from about 50 to about 140 ° C, and is most preferred from about 80 to about 110 ° C. At temperatures greater than about 180 ° C, the raw materials have the tendency to begin to decompose slowly. The pressure used during the oxidation of PMIDA generally depends on the temperature used. Preferably, the pressure is sufficient to prevent boiling of the reaction mixture. If a gas containing oxygen is used as the source of oxygen, preferably also the pressure must be adequate to cause the oxygen to dissolve in the reaction mixture at a sufficient rate so that the oxidation of PMIDA is not limited by a inadequate oxygen supply. Preferably, the pressure is at least equal to the atmospheric pressure. It is highly preferred that the pressure is from about 2.1 to about 35 kg / cm2, and better still from about 2.1 to 9.1 kg / cm2. The catalyst concentration is preferably from about 0.1 to about 10% by weight ([mass of catalyst -r- total reaction mass] x 100%). Preferably, the catalyst concentration is from about 0.2 to about 5% by weight, and better still from about 0.3 to about 1.5% by weight. Concentrations greater than about 10% by weight are difficult to filter. On the other hand, lower concentrations of about 0.1% by weight tend to produce unacceptably low reaction rates. The concentration of the PMIDA reagent in the feed stream is not critical. The use of a saturated solution of PMIDA reagent in water is preferred, although for ease of operation, the process can also work at lower or higher concentrations of PMIDA reagent in the feed stream. If the catalyst is present in the reaction mixture in a finely divided form, it is preferred to use a reagent concentration such that all reagents and the N- (phosphonomethyl) glycine product remain in solution so that the catalyst can be recovered for its reuse, for example, by filtration. On the other hand, higher concentrations tend to increase reactor performance. Alternatively, if the catalyst is present as a stationary phase through which the reaction medium and oxygen source pass, it may be possible to use higher concentrations of reagents to precipitate a portion of the N- (phosphonomethyl) glycine product. It should be recognized that, with respect to many commonly practiced commercial processes, this invention allows higher temperatures and concentrations of PMIDA reagent to be used to prepare N- (phosphonomethyl) glycine, while decreasing the formation of by-products. In commercial processes commonly practiced using a carbon-only catalyst, it is beneficial to decrease the formation of the NMG by-product formed by the reaction of N- (phosphonomethyl) glycine with the by-product formaldehyde. With these processes and catalysts, temperatures of about 60 to 90 ° C and concentrations of PMIDA reagent below about 9.0% by weight ([mass of PMIDA reagent -f- total reaction mass] x 100%) are typically used. , to achieve effective returns in cost and reduce the generation of waste. At these temperatures, the maximum solubility of N- (phosphonomethyl) glycine is typically less than 6.5%. However, with the oxidation catalyst and the reaction methods of this invention, the noble metal loss of the catalyst and catalyst deactivation have been minimized, and formaldehyde is oxidized more effectively, thus allowing reaction temperatures of up to 180.degree. ° C or greater with PMIDA reagent solutions and suspensions of PMIDA reagent. The use of higher temperatures and concentrations in the reactor, allows to increase the performance of the reactor, reduces the amount of water that must be removed before isolation of the N- (phosphonomethyl) glycine solid, and reduces the manufacturing cost of N- (phosphonomethyl) glycine. Thus, this invention provides economic benefits over many commonly practiced commercial procedures. Typically, a concentration of PMIDA reagent of up to about 90% by weight ([mass of PMIDA reagent-total reaction mass) x 100%) can be used, especially at a reaction temperature of about 20 to about 180. ° C). Preferably, a concentration of PMIDA reagent of up to about 25% by weight (particularly at a reaction temperature of about 60 to about 150 ° C) is used. Preferably, a concentration of PMIDA reagent of about 12 to about 18% by weight (particularly at a reaction temperature of about 100 to about 130 ° C) is used. PMIDA reagent concentrations can be used below 12% by weight, but their use is less economical because less N- (phosphonomethyl) glycine product is produced in each reactor cycle, more water has to be removed and it has to be removed. use more energy per unit of N- (phosphonomethyl) glycine product produced. Frequently, lower temperatures (ie temperatures below 100 ° C) tend to be less advantageous because at these temperatures both the solubility of the PMIDA reagent and the N- (phosphonomethyl) glycine product is reduced. . The oxygen source for the oxidation reaction of PMIDA can be any gas containing oxygen or a liquid comprising dissolved oxygen. Preferably, the oxygen source is a gas containing oxygen. As used herein, "oxygen-containing gas" is any gaseous mixture containing molecular oxygen and which optionally may contain one or more diluents that are not reactive with oxygen or with the reagent or product under the reaction conditions. Examples of these gases are air, pure molecular oxygen, or molecular oxygen diluted with helium, argon, nitrogen or other non-oxidizing gases. For economic reasons, preferably the oxygen source is pure air or molecular oxygen. Oxygen can be introduced by any conventional means into the reaction medium, such that the concentration of oxygen dissolved in the reaction mixture is maintained at the desired level. If a gas containing oxygen is used, it is preferably introduced into the reaction medium in such a manner as to maximize the contact of the gas with the reaction solution. Such contact can be obtained, for example, by dispersing the gas through a diffuser such as for example a porous frit or stirring, shaking, or other methods known to the person skilled in the art. Preferably, the oxygen feed rate is such that the oxidation reaction rate of PMIDA is not limited by the oxygen supply. If the concentration of dissolved oxygen is too high, however, the surface of the catalyst tends to oxidize badly, which in turn, tends to produce more leaching and reduction of formaldehyde activity (which, in turn, causes it to be produced more NMG). In general, it is preferred to use an oxygen feed rate such that at least about 40% oxygen is used. Preferably, the oxygen feed rate is such that at least about 60% of the oxygen is used. Preferably, the oxygen feed rate is such that at least about 80% of the oxygen is used. And it is even better that the speed is such that at least approximately 90% of the oxygen is used. As used herein, the percentage of oxygen used is equal to: (the total oxygen consumption rate -I- the oxygen feed rate) x 100%. The term "total oxygen consumption rate" means the sum of: (i) the rate of oxygen consumption ("R") of the oxidation reaction of the PMIDA reagent to form the N- (phosphonomethyl) glycine product and formaldehyde, (ii) the rate of oxygen consumption ("R¡,") of the reaction of oxidation of formaldehyde to formic acid, and (ii) the rate of oxygen consumption ("R¡i¡") of the reaction Oxidation of formic acid to form carbon dioxide and water. In one embodiment of this invention, oxygen is fed into the reactor as described above, until most of the PMIDA reagent has been oxidized, and then a reduced oxygen feed rate is used. This reduced feed rate is preferably used after approximately 75% of the PMIDA reagent has been consumed. Most preferably, the reduced feed rate is used after approximately 80% of the PMIDA reagent has been consumed. The feed rate can be reduced by purging the reactor with air, preferably at a volumetric feed rate not greater than the volumetric rate at which the pure molecular oxygen was fed before the air purge. Preferably, the oxygen feed rate is kept low for about 2 to about 40 minutes, preferably about 5 to about 20 minutes, and about 5 to about 15 minutes is most preferred. While the oxygen is fed at the reduced rate, the temperature is preferably maintained at the same temperature, or at a lower temperature, than the temperature at which the reaction was performed before the air purge. Also, the pressure is maintained at the same pressure, or at a pressure less than the pressure at which the reaction was performed before the air purge. The use of a reduced oxygen feed rate near the end of the PMIDA reaction tends to reduce the amount of residual formaldehyde present in the reaction solution, without producing harmful amounts of AMPA by oxidation of the N- (phosphonomethyl) product. glycine. With this invention, reduced losses of noble metal can be observed if a sacrificial reducing agent is maintained or introduced into the reaction solution. Suitable reducing agents include formaldehyde, formic acid and acetaldehyde. Preferably, formic acid, formaldehyde or mixtures thereof are used. Experiments carried out in accordance with this invention indicate that if small amounts of formic acid, formaldehyde or a combination thereof are added to the reaction solution, the catalyst will preferably effect the oxidation of formic acid or formaldehyde before it carries out the oxidation of the reagent. of PMIDA, and subsequently will be more active in carrying out the oxidation of formic acid and formaldehyde during the oxidation of PMIDA. Preferably, about 0.01 to about 5.0% by weight ([formic acid mass, formaldehyde or a combination thereof - total reaction mass] x 100%) of sacrificial reducing agent is added, preferably about 0.01 is added. to about 3.0% by weight of sacrificial reducing agent, and it is highly preferred to add from 0.01% to 1.0% by weight of sacrificial reducing agent. In a preferred embodiment, formaldehyde and formic acid that did not react are recycled back into the reaction mixture for use in subsequent cycles. In this case, the recycle stream can also be used to solubilize the PMIDA reagent in subsequent cycles. Generally, the concentration of N- (phosphonomethyl) glycine in the product mixture can be up to 40% by weight, or higher. Preferably, the concentration of N- (phosphonomethyl) glycine is from about 5 to about 40%, preferably from about 8 to about 30%, and from about 9 to about 15% is most preferred. The formaldehyde concentrations in the product mixture are generally less than about 0.5% by weight, preferably less than about 0.3%, and it is highly preferred that they be less than about 0.15%. After oxidation, preferably the catalyst is subsequently removed by filtration. The N- (phosphonomethyl) glycine product can then be isolated by precipitation, for example, by evaporation of a part of the water and cooling.

It should be recognized that the catalyst of this invention has the ability to be reused for several cycles, depending on how much its surface is oxidized with use. Even after the catalyst becomes strongly oxidized, it can be reused by reactivation. To reactivate a catalyst having a strongly oxidized surface, the surface is preferably first washed to remove the organic material from the surface. Then, it is preferably reduced in the same manner as the catalyst is reduced after depositing the noble metal on the surface of the support, as described above.

EXAMPLES The following examples are intended to illustrate and further explain the process of the present invention.

EXAMPLE 1 Measurement of the pore volume of the carbon support A Micromeritics ASAP 2000 surface area and pore volume distribution instrument was used to acquire the data. The determination of total surface area includes exposing a known weight of a solid, at a certain pressure determined from a non-specific adsorbate gas, at a constant temperature, for example, at the temperature of liquid nitrogen, -196 ° C. During equilibrium, gas molecules leave the mass of gas to adsorb on the surface, which causes a decrease in the average number of molecules in the gas mass, which in turn, reduces the pressure. The relative pressure at equilibrium, p, is recorded as a fraction of the vapor saturation pressure, po, of the gas. By combining this pressure decrease with the container and sample volumes, the amount of adsorbed gas (ie, the number of molecules) can be calculated by applying the laws of ideal gases. These data are measured at relative pressures (w / w) of approximately 0.1 to 0.3, where the Brunauer, Emmett and Teller equation (BET) is typically applied for multiple layer adsorption. Once the number of gas molecules adsorbed is known, it is possible to calculate the surface area using the "known" cross-sectional area of the adsorbate. For cases where only physical adsorption occurs due to Van der Waals forces (ie, Langmuir type I isotherms), the determination of the surface area from the observed changes in pressure is made using the BET equation . Pore size and pore size distributions are calculated by obtaining relative pressure data that approximates p / po = 1, that is, in the regime where multiple layer adsorption and capillary condensation occur. By applying the Kelvin equation and the methods developed by Barret, Joyner and Halenda (BJH), the volume and pore area can be obtained.

EXAMPLE 2 Deoxygenation at high temperature of a carbon support The high temperature deoxygenation processes described in the following examples can be used with any carbon support to produce a deoxygenated carbon support.

Deoxygenation # 1 at high temperature in a single step using NH3 / H2O gas An activated carbon support (2.5 g) was placed in a quartz tube of 1.9 cm D.l. x 40.6 cm in length. The tube was connected to a gas stream originating from the spray at 70 to 100 ml / min of a stream of N2 through an aqueous solution of 10% NH OH at 70 ° C. The quartz tube was then placed in a preheated 30.5 cm tubular furnace and pyrolyzed at 930 ° C for 60 minutes, and then cooled to room temperature under a dry N2 atmosphere without any contact with air.

Deoxygenation # 2 at high temperature in a single step using an activated carbon support (3.55 g) was placed in a quartz tube of 1.9 cm D.l. x 35.6 cm in length. The tube was connected to 50 ml / min NH3 gas streams and 89 ml / min of steam and placed in a preheated 30.5 cm tubular furnace and pyrolyzed at 930 ° C for 30 minutes. The tube was then cooled to room temperature under a dry N2 atmosphere without any contact with air. To show the advantages of deoxygenation of the carbon support before dispersing the noble metal on the surface of the support, the yields of the following two catalysts were compared: one having a carbon support that was deoxygenated using the previous treatment before dispersing platinum on its surface; and one that had a carbon support SA-30 (Westvaco Corp. Carbon, Department Covington, Virginia), which was used as received from Westvaco. Platinum was dispersed on the surfaces of the carbon supports using the technique described in Example 3 below. Then the catalysts were reduced. In one experiment, the catalysts were reduced using NaBH 4 (see example 12 for the protocol). In a second experiment, the catalysts were reduced by heating them in 20% H2 and 80% argon for 8 hours at 640 ° C. The reduced catalysts were used to catalyze the oxidation of PMIDA to N- (phosphonomethyl) glycine (ie, "glyphosate") using the reaction conditions outlined in example 5. Table 1 shows the results. The use of the deoxygenated carbon support resulted in smaller values of CO desorption, lower noble metal leaching, higher formaldehyde activity and shorter reaction times.

TABLE 1 Effect of deoxygenation of the carbon support before dispersing the noble metal on its surface or 1 When > 98% of the PMIDA had been consumed EXAMPLE 3 Twenty grams of NUCHAR SA-30 activated carbon (Westvaco Corp. Carbon, Department Covington, Virginia) was suspended in 2 liters of water for 2 hours. Then, 2.81 grams of H2PtCI6 dissolved in about 900 ml of water were added dropwise over a period of 3 to 4 hours. After completely adding the H2PtCl6 solution, the suspension was stirred for a further 90 minutes. The pH of the suspension was then adjusted to 10.5 using NaOH, and stirred for another 10 to 14 hours. The resulting suspension was filtered and washed with water until the filtrate reached a constant conductivity. The wet cake was dried at 125 ° C under vacuum for 10 to 24 hours. This material produced 5% carbon platinum by reduction. It should be recognized that the above procedure can also be used to deposit platinum on the surface of other carbon supports.

EXAMPLE 4 Reduction with hydrogen at high temperature of a carbon support Approximately 5.8 g of an unreduced dry catalyst consisting of 5% platinum on a carbon support NUCHAR SA-30 (Westvaco Corp. Carbon, Department Covington, Virginia) was dehydrated in situ at 135 ° C in argon for one hour before being reduced to 640 ° C with 20% H2 in argon for 11 hours. After cooling to room temperature under 20% H2 in argon, the catalyst was ready for use. It should be recognized that the above procedure can also be used to heat other carbon supports.

EXAMPLE 5 Use of the catalyst to oxidize PMIDA to N- (phosphonomethyl) glycine This example demonstrates the use of gas phase reduction at high temperature to improve catalyst performance. An Aldrich catalyst consisting of 5% platinum was heated on an activated carbon support (catalog No. 20,593-1, Aldrich Chemical Co., Inc., Milwaukee, Wisconsin) at 640 ° C for 4 to 6 hours in the presence of H2 20% and argon 80%. Subsequently, it was used to catalyze the oxidation of PMIDA to glyphosate. Its performance was compared to the performance of a sample of the Aldrich catalyst that was used as received from Aldrich. The oxidation reaction of PMIDA was carried out in a 200 ml glass reactor using 11.48 g of PMIDA, 0.5% catalyst (dry basis), a total reaction mass of 140 g, a temperature of 90 ° C, a pressure of 3.5 kg / cm2, a stirring speed of 900 rpm, and an oxygen flow rate of 100 ml / min.

Table 2 shows the results. The catalyst reduced with hydrogen at high temperature had less leaching, better formaldehyde activity, and produced less NMG. The reaction time was also decreased by 30% when the reduced catalyst was used with high temperature hydrogen.

TABLE 2 Oxidation of PMIDA Results for Pt 5% on activated carbon (Aldrich cat. No. 20,593-1) ^ EXAMPLE 6 Further examples showing the use of the catalyst to oxidize PMIDA to N- (phosphonomethyl) qlicine This example demonstrates the use of the gas phase reduction treatment at high temperature and washing with ammonia to improve the performance of the catalyst. The yields of six catalysts in the PMIDA catalysis were compared. These catalysts were: (a) a catalyst consisting of 5% platinum on activated carbon support (Catalog No. 33.015-9, Aldrich Chemical Co., Inc., Milwaukee, Wisconsin); (b) the catalyst after having been washed with ammonia (washing with ammonia was carried out using the same technique described in Example 10, except that the pH of the catalyst suspension was adjusted to 11.0 and remained so, instead of 9.5); (c) the catalyst after having been heated to 75 ° C in 20% H2 and 80% argon for 4 to 6 hours (GPR @ 75 ° C); (d) the catalyst after having been heated at 640 ° C for 4 to 6 hours in the presence of 20% H2 and 80% argon (GPR @ 40 ° C); and (e) two catalysts after being washed with ammonia and after being heated at 640 ° C for 4-6 hours in the presence of 20% H2 and 80% argon. The conditions of the PMIDA oxidation reaction were the same as in Example 5. Table 3 shows the results. The untreated catalyst showed relatively high leaching and deficient formaldehyde activity. The reduction in gas phase at high temperature of 640 ° C in the presence of H2 leads to the greatest decrease in leaching and increase in formaldehyde activity. Heating the catalyst to 75 ° C in 20% H2 at 75 ° C decreased the leaching to a lesser degree, but did not increase the formaldehyde activity.

TABLE 3 Oxidation results of PMIDA for Pt 5% on activated carbon (Aldrich Cat. No. 33.015-9) 1 1 .. GPR "means reduction in H2" ND "means not detected In the next experiment, five catalysts were analyzed while catalysing the oxidation of PMIDA. These catalysts were: a catalyst consisting of 5% platinum on NUCHAR SA-30 (Westvaco Corp., Coal Department, Covington, Virginia); (b) the catalyst after being treated with NaBH 4 (see example 12 for the protocol); (c) the catalyst after having been heated to 75 ° C in 20% H2 and 80% argon for 4-6 hours (GPR @ 75 ° C); (d) the catalyst after being heated to 640 ° C in 20% H2 and 80% argon for 4-6 hours (GPR @ 640 ° C); (e) the catalyst after being washed with ammonia (using the same technique as described in Example 10) and after having been heated to 640 ° C in H2 20% and argon 80% for 4-6 hours. The reaction conditions were the same as those of Example 5. Table 4 shows the results. The untreated catalyst showed relatively high platinum leaching and low formaldehyde activity. The catalyst also showed high leaching and low formaldehyde activity after being treated with NaBH4, as was GPR @ 75 ° C. On the contrary, with GPR @ 640 ° C, it showed a higher formaldehyde activity and less leaching.

TABLE 4 Oxidation results of PIDA using Pt 5% on NUCHAR SA-30 EXAMPLE 7 Effect of the C / O and O / Pt ratios on the catalyst surface The ratios of carbon atoms to oxygen atoms and oxygen atoms to platinum atoms on the surfaces of several new catalysts were analyzed using an ESCA PHI Quantum 2000 Micro Test Spectrometer (Physical Electronics, Eden Prairie, Minnesota). The surface analysis was performed by electronic spectroscopy for chemical analysis ("ESCA") with the instrument in a delay mode with the analyzer at fixed bandpass power (constant resolution). The analysis involves irradiation of the sample with soft X-rays, for example, Al Ka (1486.6 eV), whose energy is sufficient to ionize the nucleus and valence electrons. The electrons expelled leave the sample with a kinetic energy that is equal to the difference between the exciting radiation and the "binding energy" of the electron (ignoring the effects of the work function). As only the elastic electrons, that is, those that have not suffered any loss of energy by any inelastic event, are measured in the photoelectronic peak, and since the mean inelastic free path of the electrons in the solids is short, the ESCA is inherently a sensitive surface technique. The kinetic energy of electrons is measured using an electrostatic analyzer, and the number of electrons is determined using an electronic multiplier. The data is presented as the number of electrons detected against the binding energy of the electrons. ESCA study spectra were taken using monochromatic Al X-rays for the excitation of the photoelectrons with the analyzer set at a bandpass energy of 117 eV. The X-ray source was operated at 40 watts of power and data from the 200 μm point were collected on the irradiated sample. These conditions give high sensitivity but low resolution energy. Spectra were accumulated by taking a step size of 1.0 eV through the region of 1100 eV to 0 eV, and coagulating repetitive sweeps to obtain acceptable signal / noise in the data. The elements present were identified and quantified using the standard data processing and analysis procedures provided in the instrumentation by the vendor. The relative atomic concentrations of the Pt / C / O elements were obtained from the relative intensities of the photoelectronic peaks. It is generally cited that the ESCA analysis has an accuracy of ± 20% using tabulated response factors for a particular instrumental configuration. Table 5 shows the C / O and P / Pt ratios on the surface of each new catalyst, and the amount of leaching for each of the catalysts during a single cycle of PMIDA oxidation reaction.

TABLE 5 Effects of C / O and O / Pt ratios during the oxidation of PMIDA1 Catalyst Treatment of Reí. C / O Reí. O / Pt Pt in CH2O sun reduction. (mg / g) 3 after (μg / g) 2 noble metal deposition Pt 5% on NaBH4 23.7 ND4 oxygen reduced carbon The same Pt (ll) 6 35.3 17 1.2 24.44 640 ° C / 9hr / H2 10% The same NaBH4 21.1 6.9 reduced Aldrich cat. 640 ° C / 6hr / 67.9 5.2 13.78 No.33015-9 H2 20% Same 75 ° C / 6hr / 13.4 10 27.5 19.85 H220% The same Used as 13.3 10 42.6 19.39 as received Aldrich cat. 640 ° C / 6hr / 45.2 10.5 21.90 No.20593-1 H220% washed with NH ^ pH = 11 Same 640 ° C / 6hr / 37.7 10 10.5 14.60 H2 20% Same Used as 9.1 26 32.3 32.96 as received TABLE 5 (CONTINUED) Effects of the C ratios / O v O / Pt during the oxidation of PMIDA Catalyst Treatment D of Reí. C / O Reí. O / Pt Pt in CH2O sun reduction. (mg / g) 3 ddeessppuuééss ddee (μg / mg) 2 deposition of noble metal Pt 5% above 640 ° C / 7hr / H2 67.7 19.3 20.79 SA-30, car20% washed Westvaco bonus with NHs / pH = 9.5 Same 640 ° C / 8hr / 63.3 8 30.9 19.67 H220% Same 75 ° C / 7hr / 13.2 32 81.3 48.52 H220% 1 The reaction conditions were the same as those used in Example 5. 2 μg of Pt that was leached into the solution per gram of glyphosate produced. 3 mg formaldehyde per gram of glyphosate produced. 4"ND" means not detected. The carbon support was deoxygenated using the # 2 deoxygenation technique at high temperature in a single step, described in example 2. 6 Pt was deposited using diaminodinitrite of P (ll), as described in example 11.

EXAMPLE 8 Analysis of catalyst surface using thermogravimetric analysis with in-line mass spectroscopy (TGA-MS) The concentration of oxygen-containing functional groups on the surfaces of several new catalysts was determined by means of thermogravimetric analysis with in-line mass spectroscopy (TGA-MS) under helium. To perform this analysis, a dry sample (100 mg) of new catalyst is placed in a ceramic cup on a Mettler balance. The atmosphere surrounding the sample is then purged with helium, using a flow rate of 150 ml / min at room temperature for 10 minutes. Subsequently the temperature is raised to 10 ° C per minute from 20 to 900 ° C, and then it is maintained at 900 ° C for 30 minutes. The desorption of carbon monoxide and carbon dioxide is measured by a mass spectrometer calibrated in a separate experiment using a calcium oxalate sample monohydrate under the same conditions. Table 6 shows the amount of carbon monoxide desorbed per gram of each catalyst using TGA-MS, and the amount of leaching for each of the catalysts during a one-step PMIDA oxidation reaction using the same reaction conditions as in example 5. As shown in table 6, leaching tends to decrease as the amount of CO desorption decreases, and is particularly low when the desorption is not greater than 1.2 mmoles / g (mmoles of CO desorbed per gram of catalyst) .

TABLE 6 Effects of oxygen-containing functional groups desorbing from the catalyst surface as CO during TGA-MS Catalyst Treatment TGA-MS Pt in sun. Reduction CH2O (mmoles / g) 1 (μg / g) 2 (mg / g) 3 Aldrich cat. 640 ° C / 6hr / H220% 0.41 5.2 13.78 # 33015-9 The same 640 ° C / 6hr / H2 20% 0.38 5.3 15.70 washing with NH3 / pH = 9.5 The same 75 ° C / 6hr / H2 20% 1.87 27.5 19.85 The same Wash NH3 / pH = 9.5 1.59 40.7 22.73 The same Used as 1.84 42.6 19.39 was received 1 mmoles of CO per gram of catalyst. 2 μg of noble metal leached in the solution per gram of glyphosate produced. 3 mg formaldehyde per gram of glyphosate produced.

EXAMPLE 9 Effect of temperature on gas phase reduction at high temperature This example demonstrates the effects of the use of various temperatures when the catalyst is heated in the presence of a reducing agent. An unreduced catalyst having 5% platinum was heated on an activated carbon support (which had been deoxygenated using the # 2 deoxygenation technique at high temperature in a single step as described in Example 2, before depositing the platinum) , at different temperatures in H2 10% and argon 90% for approximately 2 hours. The catalyst was then used to catalyze the oxidation reaction of PMIDA.

The reaction was carried out in a 250 ml glass reactor using 5 g of PMIDA, 0.157% catalyst (on dry basis), 200 g of total reaction mass, a temperature of 80 ° C, a pressure of 0 kg / cm2 , and an oxygen flow rate of 150 ml / min. The results are shown in table 7. The increase in the reduction temperature from 125 ° C to 600 ° C reduces the amount of noble metal leaching and increases the oxidation activity of formaldehyde during the oxidation reaction of PMIDA in glyphosate.

I TABLE 7 Effects of temperature reduction Pt temperature in sun CH2O Reí. I laughed the reduction (norm (normC / O O / Pt (° C) 1) 2) 125 1.00 0.41 26 13 200 0.44 0.80 27 14 400 0.18 0.93 42 10 500 0.14 0.95 32 14 600 0.06 1.00 40 11 1 A normalized value of 1.00 corresponds to the highest amount of Pt observed in solution during this experiment. 2 A normalized value of 1.00 corresponds to the highest formaldehyde activity during this experiment.

EXAMPLE 10 Catalyst Washing with Ammonia An unreduced catalyst (6.22 g) consisting of 5% platinum was suspended on an activated carbon support (which had been deoxygenated using the # 2 deoxygenation technique at high temperature in a single step as described in Example 2, before deposit the platinum on the support), in 500 ml of water for 30 minutes. Then, the pH of the suspension was adjusted to 9.5 with dilute aqueous ammonia, and the suspension was stirred for one hour, with aqueous ammonia being added periodically to maintain the pH at 9.5. The resulting suspension was filtered and washed once with approximately 300 ml of water. The wet cake was then dried at 125 ° C under vacuum for about 12 hours. This catalyst was heated at 640 ° C for 11 hours in 10% H2 and 90% argon, and then compared with two other catalysts consisting of 5% platinum on activated carbon NUCLEAR: (a) one reduced at room temperature with NaBH4 (see example 12 for the protocol), and (b) the other heated to 640 ° C in H2 10% and argon 90% for 11 hours. The reactions were the same as those of Example 5. The results are shown in Table 8. The lowest platinum leaching was with the catalyst that had been flushed with ammonia before reduction with high temperature hydrogen.

TABLE 8 Effects of washing with ammonia Catalyst CH2O HCO2H NMG Pt in sol (mg / g) 1 (mg / g) (mg / g) (μg / g) Wash-NH, 10.62 28.79 0.83 0.50 Red. H2 High temp. Red. H2, 14.97 27.82 1.38 4.64 High temp. Network. NaBH4, 28.51 70.16 2.59 8.64 Temp. amb These amounts are per gram of glyphosate produced EXAMPLE 11 Use of a less oxidant noble metal precursor Platinum was deposited on an activated carbon support using platinum (II) diaminodinitrite. Approximately 20 g of an activated carbon support was deoxygenated using the # 2 high-temperature one-step deoxygenation technique described in Example 2. It was then suspended in 2 liters of water for 2 hours. Approximately 51.3 g of a 3.4% solution of platinum (II) diaminodinitrite, diluted to 400 g with water, were added in the form of drops over a period of 3-4 hours. After the addition was complete, stirring was continued for a further 90 minutes. The pH was adjusted again to 10.5 by adding dilute aqueous NaOH, and stirring was carried out for an additional 10-14 hours. Then, the suspension was filtered and washed with an abundant amount of water until the filtrate reached constant conductivity. The wet cake was dried at 125 ° C under vacuum for 10-24 hours. The resulting catalyst was heated at 640 ° C for 4-6 hours in 10% H2 and 90% argon. A control was prepared using H2PtCI6 to deposit platinum on the same carbon. The control was heated under the same conditions as the catalyst prepared using platinum (II) diaminodinitrite.

These catalysts were compared while catalysing the oxidation reaction of PMIDA. The reaction conditions were the same as those of example 5. The catalyst prepared using platinum (II) diaminodinitrite showed less leaching than the control. Only 1.21 μg of platinum per gram of glyphosate produced was leached into the solution, which was about three times better than the control.

EXAMPLE 12 Reduction of catalyst surface using NaBH4 The purpose of this example is to demonstrate the effects of catalyst reduction using NaBH4. Approximately 5 g of an activated carbon support (which had been deoxygenated using the # 2 deoxygenation technique at high temperature in a single step described in example 2, before depositing the platinum on the support) was suspended, with 85 my distilled water in a 250 ml round bottom flask. The suspension was stirred under vacuum for about 1 hour. Then 0.706 g of H2PtCI6 in 28 ml of distilled water was added to the suspension, at a rate of approximately 1 ml per 100 seconds, still applying vacuum. After stirring overnight in vacuum, the reactor was brought to atmospheric pressure admitting a flow of N2. After allowing the suspension to settle, approximately 30 ml of colorless supernatant were decanted. The resulting suspension was transferred to a 100 ml round bottom Teflon flask. At this point, the pH was adjusted to 12.2 with 0.3 g of NaOH. Then, 2.3 ml of NaBH 4 in 14 M NaOH was added at 0.075 ml / min. Subsequently, the resulting suspension was stirred for one hour, filtered and washed five times with 50 ml of distilled water. The catalyst was then dried at 125 ° C and 6 mm Hg for 12 hours. The resulting catalyst was used to catalyze the oxidation of PMIDA. The reaction was carried out in a 300 ml stainless steel reactor using 0.5% catalyst, 8.2% PMIDA, a total reaction mass of 180 g, a pressure of 4.55 kg / cm2, a temperature of 90 ° C, a speed of agitation of 900 rpm, and an oxygen feed rate of 72 ml / min. A control experiment was also conducted at the same reaction conditions using 5.23% platinum on an activated carbon support (which was deoxygenated using the # 2 deoxygenation technique at high temperature in a single step as described in example 2, before depositing the platinum on the support). Table 9 shows the results using the reduced catalyst with NaBH4, and Table 10 shows the results of the control experiment. The reduction with NaBH 4 decreased the amount of noble metal leaching. The amount of formaldehyde and NMG also decreased after a period of use.

TABLE 9 Results using catalyst treated with NaBH? Operation # 1 2 3 4 5 6 Glyphosate (%) 5.79 5.81 5.75 5.74 5.79 5.77 PMIDA (%) 0.23 0.08 0.13 0.22 0.13 0.13 CH2O (mg / g glyph.) 28.5 31.5 47.8 38.8 41.6 45.8 HCO2H (mg / g glyph.) 70.2 90.5 100.5 96.6 98.8 99.0 AMPA / MAMPA (%) 0.02 0.01 0.01 0.01 0.01 0.01 NMG (mg / g glyph.) 2.6 3.6 3.6 4.2 4.7 4.7 Pt in sunshine. (μg / g glyph) 8.64 8.60 5.22 6.96 6.91 5.20 Loss of Pt 0.20 0.20 0.12 0.16 0.16 0.12 TABLE 10 Results using catalyst that was not treated with NaBH? Operation # 1 2 3 4 5 6 Glyphosate (%) 5.36 5.63 5.37 5.50 5.56 5.59 PMIDA (%) 0.18 0.15 0.25 0.21 0.18 0.23 CH2O (%) 20.9 23.6 38.4 44.2 47.7 58.3 HCO2H (%) 27.8 63.8 96.5 98.4 102.2 102.0 AMPA / MAMPA (%) 0.04 0.02 0.04 0.02 0.02 0.03 NMG (mg / g glyph.) 1.5 3.0 5.4 6.9 10.6 7.3 Pt in sunshine. (μg / g glyph) 63.6 62.2 44.7 34.6 28.8 28.6 % loss of Pt 1.30 1.34 0.92 0.73 0.61 0.61 EXAMPLE 13 Use of bismuth as a promoter 500 g of a solution consisting of 10 (3 M) Bi (N? 3) 3 * 5H20 in 10"3 M formic acid solution was prepared. This solution was added to 500 g of a 5% formaldehyde solution containing 6.0. g of 5% platinum on an activated carbon support. The solution was stirred at 40 ° C under N2 overnight and then filtered with a Buchner funnel. An aliquot was dried and subsequently analyzed by X-ray fluorescence. The catalyst had a drying loss ("LOD") of 63%. The dry catalyst was found to contain about 3% bismuth and 4% platinum. The following was placed in a 300 ml stainless steel autoclave: 16.4 g of PMIDA; 4.16 g of an activated carbon catalyst, 0.68 g of the above catalyst consisting of 3% bismuth / 4% platinum on its surface, and 179.4 g of water. The reaction was carried out at a pressure of 4.55 kg / cm2, a temperature of 90 ° C, an oxygen flow rate of 38 ml / min, and a stirring speed of 900 rpm. The reaction was allowed to proceed until the PMIDA was exhausted. The glyphosate solution was separated from the catalyst by filtration, and the solution was neutralized with 6 g of 50% NaOH solution. The catalyst was recycled without purging during 5 operations. An analysis of the glyphosate solution was made in each operation. Two controls were also performed in the same manner as above, except that 0.68 g of the Bi / Pt / carbon catalyst was omitted. The results are shown in table 11. The operations that had the Bi / Pt / carbon catalyst, produced lower levels of formaldehyde, formic acid and NMG in the product.

TABLE 11 Oxidation results of PMIDA using Pt / Bi / C catalyst DBNQ = detectable, but not quantified EXAMPLE 14 Deposit of a tin promoter on a carbon support An activated carbon (20 g) was suspended in approximately 2 * liters of water. Then, 0.39 g of SnCl2"2H2" was dissolved. in 500 g of 0.5% HN03. The solution was added dropwise to the carbon suspension. After all the solution had been added, the suspension was stirred for 2 hours. The pH was then adjusted to 9.5, and the suspension was stirred for a few more hours. Then, the suspension was filtered and washed with an abundant amount of water until the filtrate reached a constant conductivity. The wet cake was dried at 125 ° C under vacuum to give tin 1% on carbon. After drying, the 1% carbon tin was calcined in argon at 500 ° C for 6 hours. To deposit platinum on the carbon support, first 5 g of 1% tin on carbon was suspended in approximately 500 ml of water. Then 0.705 g of H2PtCI6 was dissolved in approximately 125 ml of water and added dropwise. After all of the H2PtCl6 solution had been added, the suspension was stirred for 2.5 hours. The pH was then adjusted to 9.5 with dilute NaOH and stirring was continued for a few more hours. Then, the suspension was filtered and washed with an abundant amount of water until the filtrate reached a constant conductivity. The wet cake was dried at 125 ° C under vacuum.

This technique produced a catalyst comprising 5% platinum and 1% carbon-based tin.

EXAMPLE 15 Deposit of an iron promoter on a carbon support Approximately 5 g of activated carbon was suspended in approximately 500 ml of water. Afterwards, 0.25 g of FeCl3"6H2" was dissolved. in 75 ml of water. The solution was added dropwise to the carbon suspension. After all the solution had been added, the suspension was stirred for two hours. The suspension was then filtered and washed with an abundant amount of water until the filtrate reached a constant conductivity. The wet cake was dried at 125 ° C under vacuum to give 1% carbon on carbon. After drying, the iron 1% on carbon was calcined in argon at 500 ° C for 8 hours. To deposit platinum on the surface of the carbon support, first 2.5 g of the iron 1% on carbon was suspended in approximately 180 ml of water. Then 0.355 g of H PtCI6 was dissolved in about 70 ml of water and added dropwise. After all the solution had been added, the suspension was stirred for three more hours. The pH was then adjusted to about 10.0 with dilute NaOH and stirring was continued for a few more hours. Then, the suspension was filtered and washed with an abundant amount of water until the filtrate reached a constant conductivity. The wet cake was dried at 125 ° C under vacuum. This technique produced a catalyst comprising 5% platinum and 1% carbon on carbon.

EXAMPLE 16 Effect of the presence of noble metal on the surface of the carbon support This example shows the advantages of using a carbon support having a noble metal on its surface to effect the oxidation of PMIDA, instead of a carbon only catalyst that has no noble metal on its surface. The oxidation reaction of PMIDA was carried out in the presence of a carbon only catalyst that was deoxygenated using the # 2 technique of high temperature deoxygenation in a single step that is described in example 2. The reaction was carried out in a reactor 300 ml stainless steel using 0.365% catalyst, 8.2% PMIDA, a total reaction mass of 200 g, a pressure of 4.55 kg / cm2, a temperature of 90 ° C, a stirring speed of 900 rpm, and an oxygen feed rate of 38 ml / min. Table 12 shows the reaction times (ie, the time in which at least 98% of the PMIDA is consumed) of 5 cycles for the carbon-only catalyst. Table 12 also shows the reaction times for the two catalysts of Pt on carbon of example 12 during 6 cycles, under the reaction conditions described in Example 12. As can be seen from Table 12, in general, the deactivation per cycle of the carbon-only catalyst tends to be greater (ie, the reaction times tend to increase more in each cycle) than the deactivation of carbon catalysts that have a noble metal on their surfaces. Particularly, deactivation appears to be less when the catalyst has been reduced with NaBH 4 after having deposited the noble metal on the surface. Without being bound by any particular theory, it is believed that the deactivation of the reduced catalyst with NaBH 4 was less than the deactivation of the other Pt catalyst on carbon because the platinum on the NaBH catalyst was leached less than the platinum on the other catalyst. Pt on carbon. See example 12, tables 9 and 10.

TABLE 12 Results using catalyst that was not treated with NaBH4 Operation # 1 4 Operating time 45.4 55.0 64.4 69.8 75.0 for carbon-only catalyst (min) Operating time 35.1 NA1 NA 35.2 35.8 35.8 for 5% carbon platinum catalyst that was reduced with NaBH4 (min) Operating time 40.4 42.0 44.2 44.1 44.9 52.7 for platinum catalyst 5.23% or on carbon (min) Available due to temperature problems.

EXAMPLE 17 Effect of the use of a catalyst comprising an alloyed noble metal with a promoter This example shows the advantages of a catalyst comprising platinum alloyed with iron. 1. Catalyst comprising platinum alloyed with iron To prepare the catalyst comprising platinum alloyed with iron, about 10 grams of an activated carbon was suspended in about 180 ml of water. Then, 0.27 grams of FeCl * 6H20 and 1.39 grams of H2PtCI6 hydrated in about 60 ml of water were co-solved. This solution was added dropwise to the carbon suspension over a period of about 30 minutes. During the addition, the pH of the suspension dropped and was maintained between about 4.4 and about 4.8 using a diluted NaOH solution (ie, a 1.0 to 2.5 molar NaOH solution). Subsequently, the suspension was stirred for a further 3 minutes at a pH of about 4.7. The suspension was then heated under N2 at 70 ° C at a rate of about 2 ° C / min, maintaining the pH at about 4.7. After reaching 70 ° C, the pH was raised slowly over a period of about 30 minutes to 6.0 with the addition of the diluted NaOH solution. Stirring was continued for a period of about 10 minutes, until the pH stabilized at about 6.0. The suspension was then cooled under N2 to about 35 ° C. Subsequently the suspension was filtered and the cake was washed 3 times with approximately 800 ml of water. The cake was then dried at 125 ° C under vacuum. This produced a catalyst containing 5% by weight of platinum and 0.5% by weight of iron on carbon, after heating to 690 ° C in H220% and Ar 80% for 1-6 hours. This catalyst was analyzed by electron microscopy as described in more detail in Example 19. Figure 1 is an image obtained by TEM of the carbon support. This image shows that the alloyed metal particles are highly dispersed and uniformly distributed throughout the carbon support (the white dots represent the metal particles, and it is believed that variations in the intensity of the background represent the change in the local density of the metal. porous carbon). The average particle size was about 3.5 nm, and the average distance between the particles was about 20 nm. Figure 2 is a typical high energy X-ray spectrum of resolution of a single metal particle of the catalyst. As shown in figure 2, both platinum and iron peaks were present (the copper peaks originated from the dispersion of the copper grids). The quantitative analysis of the high-resolution X-ray spectra of different individual metal particles showed that the composition of the particles, within the experimental error, did not vary with the size or location of the metal particles on the surface of the catalyst. 2. - Catalyst in which platinum was less alloyed with iron To prepare the Pt / Fe / C in which the platinum was less alloyed with iron (i.e., this catalyst has less platinum alloyed with iron than the first catalyst described in this example), the platinum and the iron were deposited sequentially on the surface of the carbon support. Approximately 5 grams of an activated carbon was suspended in approximately 500 ml of water. The pH was adjusted to about 5.0 with 1N HCl. Right away, 0.25 grams of FeCI3 «6H2O were dissolved in 75 ml of water. This solution was added dropwise to the carbon suspension over a period of about 60 minutes. After all the solution had been added, the suspension was stirred for about 2 hours. The pH was adjusted to 9.5 with the diluted NaOH solution, and the suspension was stirred for a few more hours. Subsequently, the suspension was filtered and washed with an abundant amount of water. The wet cake was dried at 125 ° under vacuum to produce iron 1% by weight on carbon. After drying, this iron 1% by weight on carbon was reduced with an atmosphere containing H2 20% and Ar 80% at 635 ° C for 1-6 hours. Approximately 2.5 grams of this iron, 1% by weight on carbon, was suspended in 250 ml of water. Next, approximately 0.36 grams of hydrated H2PtCI6 was dissolved in 65 ml of water, which, in turn, was added dropwise to the suspension over a period of about 60 minutes. After all the solution had been added, the suspension was stirred for 2 hours.

Then the suspension []. The cake was resuspended in 450 ml of water. After adjusting the pH of the suspension to 9.5 with the diluted NaOH solution, the suspension was stirred for about 45 minutes. Then, the suspension was filtered and washed once with 450 ml of water. The wet cake was then dried at 125 ° C under vacuum. This produced a catalyst containing platinum 5% by weight and iron 1% by weight on carbon, after reduction by heating at a temperature of 660 ° C in an atmosphere containing H220% and Ar 80% for 1-6 hours. 3. - Comparison of the two catalysts These two catalysts were compared in the catalysis of the oxidation reaction of PMIDA. The reaction conditions were the same as those of example 5. Table 13 shows the results. The first catalyst described in this example (ie, the catalyst comprising a greater amount of platinum alloyed with iron) had greater stability with respect to the activities of CH20 and HC02H; the second catalyst described in this example (ie, the catalyst comprising a smaller amount of platinum alloyed with iron) was rapidly deactivated. In addition, the first catalyst retained almost half of its iron content for 25 cycles, while the second catalyst lost most of its iron in the first cycle.

TABLE 13 Comparison of catalyst having Pt Fe alloy with catalyst having less Pt Fe alloy or EXAMPLE 18 Preparation of a Pt / Fe / Sn catalyst on carbon Approximately 10 grams of an activated carbon was suspended in approximately 90 ml of water. Then, approximately 0.2 g of SnCl2 »2H20 was dissolved in 250 ml of 0.025 M HCl. The solution was added dropwise to the carbon suspension. After all the solution had been added, the suspension was stirred for 3 hours. The pH was then adjusted slowly to 9.0 with a dilute solution of NaOH (that is, a 1.0 to 2.5 molar NaOH solution), and the suspension was stirred for a few more hours. Then, the suspension was filtered and washed with an abundant amount of water until the filtrate reached a constant conductivity. The wet cake was dried at 125 ° C under vacuum. This produced tin 0.9% by weight on carbon. Approximately 6 grams of this 0.9 wt% of tin on carbon was suspended in approximately 500 ml of water. Then approximately 0.23 grams of Fe (N03) 3 * 9H20 and 0.85 grams of H PtCI6 were co-solved in about 150 ml of water and added dropwise to the suspension. After all the solution had been added, the suspension was stirred for 4 hours and then filtered to remove excess iron (-80% by weight). The wet cake was resuspended in 480 ml of water. After adjusting the pH of the suspension to 9-10 with the diluted NaOH solution, the suspension was stirred for a few more hours. Then, the suspension was filtered and washed with an abundant amount of water until the filtrate reached a constant conductivity. The wet cake was dried at 125 ° C under vacuum. This produced a catalyst containing 4.9% by weight of Pt, 0.9% by weight of tin and 0.1% by weight of iron on carbon, after reduction at high temperature by heating to 700-750 ° C in H220% and Ar 80% for 1-6 hours.

EXAMPLE 19 Characterization of catalysts by electron microscopy Electron microscopy techniques were used to analyze the size, spatial distribution and composition of the metal particles of the catalysts prepared in Example 17. Before analyzing the catalyst, the catalyst was first embedded in an EM Bed 812 resin (Electron Microscopy Sciences , Fort Washington, Pennsylvania). The resin was then polymerized at about 60 ° C for about 24 hours. The resulting cured block was ultramicrotomized into pieces having a thickness of approximately 50 nm. These pieces were then transferred to 200 mesh copper grids for observation in an electron microscope. High resolution analytical electron microscopy experiments were carried out in a scanning transmission electron microscope dedicated to Vacuum Generators (Model No. VG HB501, Vacuum Generators, East Brinstead, Sussex, England) with an image resolution of less than 0.3 nm. The microscope was operated at 100 kV. The vacuum in the area of the probe chamber was below 10"6 Pa. A digital image acquisition system (ES Vision Data Acquisition System, EmiSpec Sys., Inc., Tempe, Arizona) was used to obtain images of high-resolution electron microscopy.A windowless energy-dispersing X-ray spectrometer (Link LZ-5 EDS Windowless Detector, Model E5863, High Wycombe Bucks, England) was used to acquire high-energy X-ray spectra of particle resolution Due to their high atomic number sensitivity, upper-angle annular dark field microscopy (HAADF) was used to observe the metal particles.An electronic probe size of less than about 0.5 nm was used to obtain the images. HAADF, and a probe size of less than about 1 nm was used to obtain high resolution energy X-ray spectra The present invention is not limited to the modalities teriores and can be modified in several ways. The above description of the preferred embodiments is only intended to familiarize other experts in the field with the invention, its principles and its practical application in such a way that other experts in the field can adapt and apply the invention in its many forms, as it may be more suitable to the requirements of a particular use.

Claims

NOVELTY OF THE INVENTION CLAIMS 1. - An oxidation catalyst comprising a carbon support having a noble metal and a promoter on a surface of the carbon support, characterized in that it produces less than 0.5 mmol of carbon monoxide per gram of catalyst when a dry sample of the catalyst, then having been heated to a temperature of about 500 ° C for about 1 hour in a hydrogen atmosphere, and before being exposed to an oxidant after heating in the hydrogen atmosphere, it is heated in a helium atmosphere at a temperature of about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for about 30 minutes; wherein said promoter constitutes at least 0.05% by weight of the catalyst, and the carbon support has a specific surface area of about 10 to about 3000 m2 / g, as measured by the Brunauer-Emmett-Teller method.
2. The oxidation catalyst according to claim 1, further characterized in that the promoter is oxidized more easily than the noble metal. 3. - The oxidation catalyst according to claim 1, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 4. The oxidation catalyst according to claim 1, further characterized in that the promoter comprises tin. 5. The oxidation catalyst according to claim 1, further characterized in that the promoter comprises iron, 6. The oxidation catalyst according to claim 1, further characterized in that the promoter comprises titanium. 7. The oxidation catalyst according to claim 1, further characterized in that it comprises two promoters on the surface of the carbon support, each of said promoters constituting at least 0.05% by weight of the catalyst. 8. The oxidation catalyst according to claim 7, further characterized in that the promoters comprise iron and tin. 9. The oxidation catalyst according to claim 1, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. l ll 10. - The oxidation catalyst according to claim 1, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 11. The oxidation catalyst according to claim 1, further characterized in that substantially all of the noble metal atoms on the surface are alloyed with the promoter. 12. The oxidation catalyst according to claim 1, further characterized in that said production of carbon monoxide is not greater than about 0.3 mmole of carbon monoxide per gram of catalyst. 13. An oxidation catalyst comprising a carbon support having a noble metal, a promoter, carbon and oxygen on a surface of the carbon support; the catalyst is characterized in that it has a ratio of carbon atoms to oxygen atoms, of at least about 30: 1 on the surface, as measured by X-ray photoelectron spectroscopy after having heated the catalyst to a temperature of about 500 ° C for about 1 hour in a hydrogen atmosphere, and before exposing the catalyst to an oxidant after heating in the hydrogen atmosphere; wherein said promoter constitutes at least 0.05% by weight of the catalyst, and the carbon support has a specific surface area of about 10 to about 3000 m2 / g, as measured by the Brunauer-Emmet-Telier method. 14. - The oxidation catalyst according to claim 13, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 40: 1. 15. The oxidation catalyst according to claim 13, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 50: 1. 16. The oxidation catalyst according to claim 13, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 60: 1. 17. The oxidation catalyst according to claim 13, further characterized in that it has a ratio of oxygen atoms to noble metal atoms on the surface, which is less than 7: 1 after heating the catalyst to a temperature of about 500 ° C for about 1 hour in a hydrogen atmosphere, and before exposing the catalyst to an oxidant after heating in the hydrogen atmosphere. 18. The oxidation catalyst according to claim 17, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 6: 1. 19. The oxidation catalyst according to claim 17, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 5: 1. 20. - The oxidation catalyst according to claim 13, further characterized in that the promoter is oxidized more easily than the noble metal. 21. The oxidation catalyst according to claim 13, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 22. The oxidation catalyst according to claim 13, further characterized in that the promoter comprises tin. 23. The oxidation catalyst according to claim 13, further characterized in that the promoter comprises iron. 24. The oxidation catalyst according to claim 13, further characterized in that the promoter comprises titanium. 25. The oxidation catalyst according to claim 13, further characterized in that it comprises two promoters on the surface of the carbon support, each of said promoters constituting at least 0.05% by weight of the catalyst. 26. The oxidation catalyst according to claim 25, further characterized in that the promoters comprise iron and tin. 27. - The oxidation catalyst according to claim 13, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 28. The oxidation catalyst according to claim 13, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 29. The oxidation catalyst according to claim 13, further characterized in that substantially all the noble metal atoms on the surface are alloyed with the promoter. 30.- An oxidation catalyst prepared by means of a process comprising depositing a noble metal on a surface of a carbon support, and then heating the surface to a temperature higher than 500 ° C in the presence of a gaseous phase reducing agent. , wherein the carbon support has a specific surface area of about 10 to about 3000 m2 / g, as measured by the Brunauer-Emmett-Teller method. 31. The oxidation catalyst according to claim 30, further characterized in that it comprises a promoter, said promoter constituting at least 0.05% by weight of the catalyst. 32. The oxidation catalyst according to claim 31, further characterized in that the promoter is oxidized more easily than the noble metal. 33. - The oxidation catalyst according to claim 31, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 34. The oxidation catalyst according to claim 31, further characterized in that the promoter comprises tin. 35.- The oxidation catalyst according to claim 31, further characterized in that the promoter comprises iron. 36. The oxidation catalyst according to claim 31, further characterized in that the promoter comprises titanium. 37. The oxidation catalyst according to claim 31, further characterized in that it comprises two promoters on the surface of the carbon support, each of said promoters constituting at least 0.05% by weight of the catalyst. 38.- The oxidation catalyst according to claim 37, further characterized in that the promoters comprise iron and tin. 39. The oxidation catalyst according to claim 31, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 40. - The oxidation catalyst according to claim 31, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 41. The oxidation catalyst according to claim 31, further characterized in that substantially all the noble metal atoms on the surface are alloyed with the promoter. 42. The oxidation catalyst according to claim 30, further characterized in that said temperature is from about 550 to about 1,200 ° C. 43. The oxidation catalyst according to claim 30, further characterized in that said temperature is from about 550 to about 900 ° C. 44. The oxidation catalyst according to claim 30, further characterized in that said heating of the surface of the support at a temperature higher than 500 ° C, is carried out in the presence of a gas selected from the group consisting of N2 and the gases noble 45. The oxidation catalyst according to claim 44, further characterized in that said gas phase reducing agent comprises H2. 46. The oxidation catalyst according to claim 30, further characterized in that said gaseous phase reducing agent comprises a gas selected from the group consisting of H2, ammonia and carbon monoxide. 47. The oxidation catalyst according to claim 30, further characterized in that said gas phase reducing agent comprises H2. 48. An oxidation catalyst prepared by means of a process comprising depositing a noble metal on a surface of a carbon support, and then heating the surface to a temperature of at least about 400 ° C, wherein: before the deposition of the noble metal, the carbon support has carbon and oxygen on its surface in quantities such that the ratio of carbon atoms to oxygen atoms on the surface is at least about 20: 1, as measured by photoelectron ray spectroscopy X; wherein the catalyst comprises a promoter that constitutes at least 0.05% by weight of the catalyst; and wherein the carbon support has a specific surface area of from about 10 to about 3000 m2 / g, as measured by the Brunauer-Emmett-Teller method. 49. The oxidation catalyst according to claim 48, further characterized in that the promoter is oxidized more easily than the noble metal. 50.- The oxidation catalyst according to claim 48, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 51.- The oxidation catalyst according to claim 48, further characterized in that the promoter comprises tin. 52. The oxidation catalyst according to claim 48, further characterized in that the promoter comprises iron. 53. The oxidation catalyst according to claim 48, further characterized in that the promoter comprises titanium. 54.- The oxidation catalyst according to claim 48, further characterized in that it comprises two promoters on the surface of the carbon support, each of the promoters constituting at least 0.05% by weight of the catalyst. 55.- The oxidation catalyst according to claim 48, further characterized in that the promoters comprise iron and tin. 56.- The oxidation catalyst according to claim 48, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 57. The oxidation catalyst according to claim 48, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 58. - The oxidation catalyst according to claim 48, further characterized in that substantially all the noble metal atoms on the surface are alloyed with the promoter. 59. The oxidation catalyst according to claim 48, further characterized in that said temperature is at least about 500 ° C. 60.- The oxidation catalyst according to claim 48, further characterized in that said temperature is from about 550 to about 1200 ° C. 61.- The oxidation catalyst according to claim 48, further characterized in that said temperature is from about 550 to about 900 ° C. 62.- The oxidation catalyst according to claim 48, further characterized in that the heating is carried out in a non-oxidizing medium. 63.- The oxidation catalyst according to claim 62, further characterized in that said temperature is at least about 500 ° C. 64.- The oxidation catalyst according to claim 62, further characterized in that said temperature is from about 550 to about 1200 ° C. The oxidation catalyst according to claim 62, further characterized in that the non-oxidizing medium consists essentially of at least one gas selected from the group consisting of N 2, and the noble gases. 66.- The oxidation catalyst according to claim 62, further characterized in that the non-oxidizing medium comprises a reducing medium. 67.- The oxidation catalyst according to claim 66, further characterized in that said temperature is at least about 500 ° C. 68.- The oxidation catalyst according to claim 66, further characterized in that said temperature is from about 550 to about 1200 ° C. 69.- The oxidation catalyst according to claim 66, further characterized in that the reducing means comprises H2. 70.- An oxidation catalyst prepared by means of a process comprising depositing a noble metal on a surface of a carbon support, and then exposing the surface to a reducing means, characterized in that, before the deposition of the noble metal, the Carbon support has carbon and oxygen on its surface in amounts such that the ratio of carbon atoms to oxygen atoms on the surface is at least about 20: 1, as measured by X-ray photoelectron spectroscopy; and wherein the catalyst comprises a promoter, said promoter constitutes at least 0.05% by weight of the catalyst. 71. - The oxidation catalyst according to claim 70, further characterized in that the promoter is oxidized more easily than the noble metal. 72. The oxidation catalyst according to claim 70, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, seienium, iron, rhenium, cerium, zinc and zirconium. 73.- The oxidation catalyst according to claim 70, further characterized in that the promoter comprises tin. 74.- The oxidation catalyst according to claim 70, further characterized in that the promoter comprises iron. 75.- The oxidation catalyst according to claim 70, further characterized in that the promoter comprises titanium. The oxidation catalyst according to claim 70, further characterized in that it comprises two promoters on the surface of the carbon support, each of the promoters constituting at least 0.05% by weight of the catalyst. 77. The oxidation catalyst according to claim 70, further characterized in that the promoters comprise iron and tin. 78. - The oxidation catalyst according to claim 70, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 79. The oxidation catalyst according to claim 70, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 80.- The oxidation catalyst according to claim 70, further characterized in that substantially all the noble metal atoms on the surface are alloyed with the promoter, 81.- The oxidation catalyst according to claim 70, further characterized in that the reducing medium comprises ammonia. 82. The oxidation catalyst according to claim 70, further characterized in that the reducing agent comprises NaBH4. 83.- A process for the preparation of an oxidation catalyst, comprising: depositing a noble metal on a surface of a carbon support, and then heating the surface to a temperature higher than 500 ° C in the presence of a reducing agent of gaseous phase, wherein the carbon support has a specific surface area of about 10 to about 3000 m2 / g, measured by the Brunauer, Emmett and Teller method. 84. - The method according to claim 83, further characterized in that said temperature is from about 550 to about 1200 ° C. 85.- The method according to claim 83, further characterized in that said temperature is from about 550 to about 900 ° C. 86.- The method according to claim 83, further characterized in that said heating of the surface of the support at a temperature greater than 500 ° C is carried out in the presence of a gas selected from the group consisting of N2 and the noble gases. 87. The method according to claim 86, further characterized in that said gas phase reducing agent comprises H2. 88.- The method according to claim 83, further characterized in that said gas phase reducing agent comprises a gas selected from the group consisting of H2, ammonia and carbon monoxide. 89.- The method according to claim 83, further characterized in that said gas phase reducing agent comprises H2. The method according to claim 83, further characterized in that it comprises exposing the surface of the carbon support to ammonia, before, during, and / or after said heating of the surface of the support at a temperature greater than 500 ° C. . 91.- The method according to claim 83, further characterized in that it comprises contacting the surface of the carbon support with a solution comprising ammonium ions. 92.- The method according to claim 91, further characterized in that it comprises contacting the surface of the carbon support with a solution comprising ammonium ions after depositing the noble metal on the surface, 93.- The process according to claim 83, further characterized in that it comprises contacting the surface of the carbon support with NaBH 4. 94. The method according to claim 83, further characterized in that it comprises removing oxygen from the surface of the carbon support before depositing the noble metal on the surface. The method according to claim 83, further characterized in that the noble metal is deposited on the surface of the carbon support, using a noble metal precursor comprising the noble metal in a state of oxidation less than the oxidation state maximum noble metal. 96.- The method according to claim 83, further characterized in that the catalyst comprises a promoter, said promoter constituting at least 0.05% by weight of the catalyst. 97. - The method according to claim 96, further characterized in that the promoter is oxidized more easily than the noble metal. The method according to claim 96, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 99. The process according to claim 96, further characterized in that the promoter comprises tin. 100.- The method according to claim 96, further characterized in that the promoter comprises iron. 101. The method according to claim 96, further characterized in that the promoter comprises titanium. 102.- The method according to claim 96, further characterized in that the catalyst comprises two promoters on the surface of the carbon support, each of said promoters constituting at least 0.05% by weight of the catalyst. 103. The method according to claim 102, further characterized in that the promoters comprise iron and tin. 104. The process according to claim 96, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 105. - The method according to claim 96, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 106. The method according to claim 96, further characterized in that substantially all the noble metal atoms on the surface are alloyed with the promoter. 107.- A process for the preparation of an oxidation catalyst of a carbon support having carbon and oxygen on its surface, the method comprising depositing a noble metal on the surface, and then heating the surface to a temperature of at least about 400 ° C, characterized in that: the ratio of carbon atoms to oxygen atoms on the surface of the carbon support is at least about 20: 1, as measured by X-ray photoelectron spectroscopy before deposition of the noble metal; wherein the catalyst comprises a promoter, said promoter constituting at least 0.05% by weight of the catalyst; and wherein the carbon support has a specific surface area of from about 10 to about 3000 m2 / g, as measured by the Brunauer-Emmett-Teller method. 108. The method according to claim 107, further characterized in that the promoter is oxidized more easily than the noble metal. The method according to claim 107, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 110.- The method according to claim 107, further characterized in that the promoter comprises tin. 111. The method according to claim 107, further characterized in that the promoter comprises iron. 112. The method according to claim 107, further characterized in that the promoter comprises titanium. 113. The method according to claim 107, further characterized in that the catalyst comprises two promoters on the surface of the carbon support, each of said promoters constituting at least 0.05% by weight of the catalyst. 114. The method according to claim 113, further characterized in that the promoters comprise iron and tin. The method according to claim 107, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. The method according to claim 107, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 117. The process according to claim 107, further characterized in that substantially all the noble metal atoms on the surface are alloyed with the promoter. 118.- The method according to claim 107, further characterized in that said temperature is at least about 500 ° C. 119.- The method according to claim 107, further characterized in that said temperature is from about 550 to about 1200 ° C. 120.- The method according to claim 107, further characterized in that said temperature is from about 550 to about 900 ° C. 121. The method according to claim 107, further characterized in that said heating is carried out in a non-oxidizing medium. 122. The method according to claim 121, further characterized in that said temperature is at least about 500 ° C. 123.- The method according to claim 121, further characterized in that said temperature is from about 550 to about 1200 ° C. 124. The method according to claim 121, further characterized in that the non-oxidizing medium consists essentially of at least one gas selected from the group consisting of N2 and the noble gases. 125. The method according to claim 121, further characterized in that the non-oxidizing medium comprises a reducing means. 126. The method according to claim 125, further characterized in that said temperature is at least about 500 ° C. 127.- The method according to claim 125, further characterized in that said temperature is from about 550 to about 1200 ° C. 128. The method according to claim 125, further characterized in that the reducing means comprises H2. 129.- A process for the preparation of an oxidation catalyst of a carbon support having carbon and oxygen on a surface of the carbon support, comprising depositing a noble metal on the surface and then exposing the surface to a reducing medium, characterized in that: the ratio of carbon atoms to oxygen atoms on the surface is at least about 20: 1, as measured by X-ray photoelectron spectroscopy before the deposition of noble metal; and wherein the catalyst comprises a promoter, said promoter comprising at least 0.05% by weight of the catalyst. 130. - The method according to claim 129, further characterized in that the promoter is oxidized more easily than the noble metal. 131. The method according to claim 129, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 132. The method according to claim 129, further characterized in that the promoter comprises tin. 133. The method according to claim 129, further characterized in that the promoter comprises iron. 134. The method according to claim 129, further characterized in that the promoter comprises titanium. The method according to claim 129, further characterized in that the catalyst comprises two promoters on the surface of the carbon support, each of said promoters constituting at least 0.05% by weight of the catalyst. 136. The method according to claim 135, further characterized in that the promoters comprise iron and tin. 137.- The method according to claim 129, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 138. - The method according to claim 129, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 139. The method according to claim 129, further characterized in that substantially all the noble metal atoms on the surface are alloyed with the promoter. The method according to claim 129, further characterized in that the reducing agent comprises ammonia. 141. The method according to claim 140, further characterized in that it comprises heating the surface to at least 400 ° C after depositing the noble metal. 142.- The method according to claim 141, further characterized in that said heating is carried out in a non-oxidizing medium. 143. The method according to claim 129, further characterized in that the reducing agent comprises NaBH4. 144. The method according to claim 143, further characterized in that it comprises heating the surface to a temperature of at least about 400 ° C after depositing the noble metal on the surface of the carbon support. 145. The method according to claim 144, further characterized in that said heating is performed in a non-oxidizing medium. 146. - A process for the preparation of an oxidation catalyst of a carbon support having carbon and oxygen on a surface of the carbon support; the method comprises depositing a noble metal on the surface and then exposing the surface to a reducing means to reduce the surface in such a way that the ratio of carbon atoms to oxygen atoms on the surface is at least about 30: 1 , measured by x-ray photoelectron spectroscopy, characterized in that the catalyst comprises a promoter that constitutes at least 0.05% by weight of the catalyst. 147. The method according to claim 146, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 40: 1. 148.- The method according to claim 146, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 50: 1. 149. The method according to claim 146, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 60: 1. 150. The method according to claim 146, further characterized in that the ratio of oxygen atoms to noble metal atoms on the surface is less than 7: 1, as measured by X-ray photoelectron spectroscopy. 151. - The method according to claim 146, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 6: 1. 152.- The method according to claim 146, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 5: 1. 153. The method according to claim 146, further characterized in that the reducing agent comprises ammonia. 154. The method according to claim 146, further characterized in that the reducing agent comprises NaBH4. 155. The method according to claim 146, further characterized in that the promoter is oxidized more easily than the noble metal. The method according to claim 146, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 157. The method according to claim 146, further characterized in that the promoter comprises tin. 158. The method according to claim 146, further characterized in that the promoter comprises iron. 159. - The method according to claim 146, further characterized in that the promoter comprises titanium. The process according to claim 146, further characterized in that the catalyst comprises at least two promoters on the surface of the carbon support, each of said promoters constituting at least 0.05% by weight of the catalyst. 161. The method according to claim 160, further characterized in that the promoters comprise iron and tin. The method according to claim 146, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 163. The method according to claim 146, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 164. The method according to claim 146, further characterized in that substantially all the noble metals on the surface are alloyed with the promoter. 165.- A process for the preparation of an oxidation catalyst, comprising depositing a noble metal on a surface of a carbon support, and then exposing the surface to a reducing means to reduce the surface, in such a way that they are desorbed from the surface. catalyst less than 0.5 mmole of carbon monoxide per gram of catalyst when a dry sample of the catalyst is heated in a helium atmosphere at a temperature of about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for about 30 minutes, characterized in that the catalyst comprises a promoter which constitutes at least 0.05% by weight of the catalyst. 166.- The method according to claim 165, further characterized in that the production of carbon monoxide is not greater than about 0.3 mmole of carbon monoxide per gram of catalyst, 167.- The method according to claim 165, characterized also because the reducing agent comprises ammonia. 168. The method according to claim 165, further characterized in that the reducing agent comprises NaBH4. 169.- The method according to claim 165, further characterized in that the promoter is oxidized more easily than the noble metal. 170. The method according to claim 165, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 171- The method according to claim 165, further characterized in that the promoter comprises tin. 172. - The method according to claim 165, further characterized in that the promoter comprises iron. 173. The method according to claim 165, further characterized in that the promoter comprises titanium. 174. The method according to claim 165, further characterized in that the catalyst comprises at least two promoters on the surface of the carbon support, each of said promoters constituting at least 0.05% by weight of the catalyst. 175. The method according to claim 174, further characterized in that the promoters comprise iron and tin. 176. The method according to claim 165, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 177. The method according to claim 165, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 178. The method according to claim 165, further characterized in that substantially all the noble metal atoms on the surface are alloyed with the promoter. 179. A process for oxidizing a reagent in a mixture, the mixture being able to solubilize a noble metal; the method comprises contacting the mixture with an oxidation catalyst in the presence of oxygen, wherein the catalyst comprises a carbon support having a noble metal on a surface of the carbon support; and wherein the catalyst produces no more than about 1.2 mmoles of carbon monoxide per gram of catalyst when a dry sample of the catalyst is heated in a helium atmosphere at a temperature of about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for about 30 minutes. 180. The method according to claim 179, further characterized in that the process is carried out in a continuous reactor system. 181. The process according to claim 179, further characterized in that the production of carbon monoxide is not greater than about 0.7 mmole of carbon monoxide per gram of catalyst. 182. The method according to claim 179, further characterized in that the mixture is acidic. 183. A process for oxidizing a reagent in a mixture that can solubilize a noble metal; the method comprises contacting the mixture with an oxidation catalyst in the presence of oxygen, wherein the catalyst comprises a carbon support having a noble metal and a promoter on a surface of the carbon support; and wherein the catalyst produces no more than about 1.2 mmol of carbon monoxide per gram of catalyst when a dry sample of the catalyst, after having been heated to a temperature of about 500 ° C for about 1 hour in a hydrogen atmosphere, and before being exposed to an oxidant after heating in the hydrogen atmosphere, it is heated in a helium atmosphere at a temperature of about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then to a temperature of about 900 ° C for about 30 minutes. 184. The method according to claim 183, further characterized in that the process is carried out in a continuous reactor system. 185. The method according to claim 183, further characterized in that the production of carbon monoxide is not greater than about 0.7 mmole of carbon monoxide per gram of catalyst. 186. The method according to claim 183, further characterized in that at least 0.05% by weight of the catalyst consists of at least one promoter. 187.- A procedure to oxidize a reagent in a mixture that can solubilize a noble metal; the method comprises contacting the mixture with an oxidation catalyst in the presence of oxygen, wherein the catalyst comprises a carbon support having a noble metal, carbon and oxygen on a surface of the carbon support, the ratio of the carbon atoms being carbon to oxygen atoms on the surface of at least about 20: 1, as measured by X-ray photoelectron spectroscopy. 188.- The method according to claim 187, further characterized in that it is carried out in a continuous reactor system. The method according to claim 187, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 30: 1. , 190.- A method for oxidizing a reagent in a mixture that can solubilize a noble metal; the method comprises contacting the mixture with an oxidation catalyst in the presence of oxygen, wherein the catalyst comprises a carbon support having a noble metal, a promoter, carbon and oxygen on a surface of the carbon support; and wherein the catalyst has a ratio of carbon atoms to oxygen atoms on the surface, which is at least about 20: 1, as measured by X-ray photoelectron spectroscopy after heating the catalyst at a temperature of about 500 ° C for about 1 hour in a hydrogen atmosphere, and before exposing the catalyst to an oxidant after heating in the atmosphere of hydrogen. 191. The method according to claim 190, further characterized in that it is carried out in a continuous reactor system. 192. - The method according to claim 190, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 30: 1. 193. The method according to claim 190, further characterized in that at least 0.05% by weight of the catalyst consists of at least one promoter. 194. A process for oxidizing a reagent in a mixture that can solubilize a noble metal, characterized in that it comprises: forming an oxidation catalyst by means of a process comprising depositing a noble metal on a surface of a carbon support, and then heating the surface to a temperature of at least about 400 ° C; and contacting the mixture with the oxidation catalyst in the presence of oxygen. 195. The process according to claim 194, further characterized in that the mixture is contacted with the oxidation catalyst in the presence of oxygen in a continuous reactor system. 196. The method according to claim 194, further characterized in that at least 0.05% by weight of the catalyst consists of at least one promoter. 197. The method according to claim 196, further characterized in that the promoter is oxidized more easily than the noble metal. 198. - The method according to claim 196, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 199. The process according to claim 196, further characterized in that the promoter comprises tin. 200. The method according to claim 196, further characterized in that the promoter comprises iron, 201.- The method according to claim 196, further characterized in that the promoter comprises titanium. 202.- The method according to claim 196, further characterized in that at least two promoters are deposited on the surface of the carbon support. 203. The method according to claim 202, further characterized in that the promoters comprise iron and tin. 204. The method according to claim 196, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 205. The method according to claim 196, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 206. - The method according to claim 196, further characterized in that substantially all of the noble metals on the surface are alloyed with the promoter. 207.- The method according to claim 194, further characterized in that said temperature is at least about 500 ° C. 208.- The method according to claim 194, further characterized in that, before the deposition of the noble metal, the carbon support has carbon and oxygen on a surface of the carbon support in amounts such that the ratio of carbon atoms to oxygen atoms on the surface is at least about 20: 1, as measured by X-ray photoelectron spectroscopy. 209. The method according to claim 194, further characterized in that said heating is performed in a non-oxidizing medium. 210.- The procedure according to claim 209, further characterized in that the non-oxidizing medium comprises a reducing medium. 211. The method according to claim 209, further characterized in that the reducing means comprises H2. 212. A method for oxidizing a reagent in a mixture that can solubilize a noble metal, characterized in that it comprises: forming an oxidation catalyst by means of a process comprising (a) depositing a noble metal on a surface of a carbon support , and (b) exposing the surface to a reducing medium; and contacting the mixture with the oxidation catalyst in the presence of oxygen, wherein, before the deposition of noble metal, the carbon support has carbon and oxygen on its surface in amounts such that the ratio of carbon atoms to atoms of oxygen on the surface, is at least 20: 1, as measured by X-ray photoelectron spectroscopy. 213. The method according to claim 212, further characterized in that the mixture is contacted with the oxidation catalyst in presence of oxygen in a continuous reactor system. 214. The method according to claim 212, further characterized in that at least 0.05% by weight of the catalyst consists of at least one promoter. 215. The method according to claim 214, further characterized in that the promoter is oxidized more easily than the noble metal. 216. The method according to claim 214, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 217- The method according to claim 214, further characterized in that the promoter comprises tin. 218. The method according to claim 214, further characterized in that the promoter comprises iron. 219. The method according to claim 214, further characterized in that the promoter comprises titanium. 220. The method according to claim 214, further characterized in that at least two promoters are deposited on the surface of the carbon support, 221. The method according to claim 220, further characterized in that the promoters comprise iron and tin. 222. The method according to claim 214, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 223. The process according to claim 214, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 224. The method according to claim 214, further characterized in that substantially all of the noble metals on the surface are alloyed with the promoter. 225.- A process for the preparation of N- (phosphonomethyl) glycine or a salt thereof, comprising contacting N- (phosphonomethyl) iminodacetic acid, or a salt thereof, with an oxidation catalyst in the presence of of oxygen, wherein the catalyst comprises a carbon support having a noble metal on a surface of the carbon support; and the catalyst produces no more than about 1.2 mmol of carbon monoxide per gram of catalyst when a dry sample of the catalyst in a helium atmosphere is heated to a temperature of about 20 to about 900 ° C, at a rate of about 10 °. C per minute, and then at a temperature of about 900 ° C for about 30 minutes. 226.- The method according to claim 225, further characterized in that it is carried out in a continuous reactor system. 227.- The method according to claim 225, further characterized in that the production of carbon monoxide is not greater than about 0.7 mmole of carbon monoxide per gram of catalyst. 228. The method according to claim 225, further characterized in that the production of carbon monoxide is not greater than about 0.5 mmol of carbon monoxide per gram of catalyst. 229.- The method according to claim 225, further characterized in that the production of carbon monoxide is not greater than about 0.3 mmole of carbon monoxide per gram of catalyst. 230. - The method according to claim 225, further characterized in that the oxidation is carried out in a solution or suspension, and oxygen is introduced into the solution or suspension at a rate such that at least about 40% of the oxygen is used. 231. The process according to claim 225, further characterized in that the oxidation is carried out in a solution or suspension, and oxygen is introduced into the solution or suspension at a rate such that at least about 60% of the oxygen is used. 232. The method according to claim 225, further characterized in that the oxidation is carried out in a solution or suspension, and oxygen is introduced into the solution or suspension at a rate such that at least about 80% of the oxygen is used. 233. The method according to claim 225, further characterized in that the oxidation is carried out in a solution or suspension, and oxygen is introduced into the solution or suspension at a rate such that at least about 90% of the oxygen is used. 234. The method according to claim 225, further characterized in that the oxidation is carried out in a solution or suspension, and oxygen is introduced into the solution or suspension at a rate such that at least about 40% of the oxygen is used up. that at least about 80% of the reagent has been consumed, and then introduced into the solution or suspension at a reduced rate to increase the oxidation of formaldehyde in the solution or suspension. 235. - The method according to claim 225, further characterized in that it comprises introducing a sacrificial reducing agent into the solution or suspension. 236. The method according to claim 235, further characterized in that the sacrificial reducing agent comprises formaldehyde, formic acid or a combination of both. 237. A process for the preparation of N- (phosphonomethyl) glycine or a salt thereof, comprising contacting N- (phosphonomethyl) iminodiacetic acid or a salt thereof with an oxidation catalyst in the presence of oxygen. , wherein the catalyst comprises a carbon support having a noble metal, carbon and oxygen on a surface of the carbon support; and the ratio of carbon atoms to oxygen atoms on the surface, is at least about 20: 1, as measured by X-ray photoelectron spectroscopy. 238. The method according to claim 237, further characterized in that it is carried out in a continuous reactor system. 239. The method according to claim 237, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 30: 1. 240. The method according to claim 237, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 40: 1. 241. - The method according to claim 237, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 50: 1. 242. The method according to claim 237, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 60: 1. 243. The method according to claim 237, further characterized in that the ratio of oxygen atoms to noble metal atoms on the surface is less than about 8: 1, as measured by X-ray photoelectron spectroscopy. 244.- The The method according to claim 243, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 7: 1. 245. The method according to claim 243, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 6: 1. 246. The method according to claim 243, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 5: 1. 247.- A process for the preparation of N- (phosphonomethyl) glycine or a salt thereof, characterized in that it comprises: forming an oxidation catalyst by means of a process comprising depositing a noble metal on a surface of a carbon support , and then heating the surface to a temperature of at least about 400 ° C; and contacting N- (phosphonomethyl) iminodiacetic acid, or a salt thereof, with the oxidation catalyst in the presence of oxygen. 248. The method according to claim 247, further characterized in that the N- (phosphonomethyl) iminodiacetic acid, or a salt thereof, is contacted with the oxidation catalyst in the presence of oxygen in a continuous reactor system. 249. The method according to claim 247, further characterized in that said temperature is at least about 500 ° C. The method according to claim 247, further characterized in that said temperature is from about 550 to about 1,200 ° C. 251. The method according to claim 247, further characterized in that said temperature is from about 550 to about 900 ° C. 252. The method according to claim 247, further characterized in that before the deposition of the noble metal, the carbon support has carbon and oxygen on its surface in amounts such that the ratio of carbon atoms to oxygen atoms in the surface, is at least approximately 20: 1, as measured by X-ray photoelectron spectroscopy. 253. - The method according to claim 247, further characterized in that said heating is carried out in a non-oxidizing medium. 254. The method according to claim 253, further characterized in that said temperature is at least about 500 ° C. 255.- The method according to claim 253, further characterized in that said temperature is from about 550 to about 1, 200 ° C. 256. The method according to claim 253, further characterized in that the non-oxidizing medium consists essentially of at least one gas selected from the group consisting of N2 and the noble gases. The process according to claim 253, further characterized in that, before the deposition of the noble metal, the carbon support has carbon and oxygen on its surface in amounts such that the ratio of carbon atoms to oxygen atoms in the surface before the deposition of the noble metal is at least about 20: 1, as measured by X-ray photoelectron spectroscopy. 258. The method according to claim 253, further characterized in that the non-oxidizing medium comprises a medium reducer. 259. - The method according to claim 258, further characterized in that said temperature is at least about 500 ° C. 260.- The method according to claim 258, further characterized in that said temperature is from about 550 to about 1200 ° C. 261. The method according to claim 258, further characterized in that the reducing means comprises H2. 262.- The method according to claim 258, further characterized in that, before the deposition of the noble metal, the carbon support has carbon and oxygen on its surface in amounts such that the ratio of carbon atoms to oxygen atoms in the surface before the deposition of the noble metal is at least about 20: 1, as measured by X-ray photoelectron spectroscopy. 263. A process for the preparation of N- (phosphonomethyl) glycine or a salt thereof, characterized in that it comprises forming an oxidation catalyst by means of a process comprising (a) depositing a noble metal on a surface of a carbon support, and (b) exposing the surface to a reducing medium; and contacting N- (phosphonomethyl) iminodiacetic acid, or a salt thereof, with the oxidation catalyst in the presence of oxygen, wherein, before the deposition of the noble metal, the carbon support has carbon and oxygen on its surface in amounts such that the ratio of carbon atoms to oxygen atoms on the surface is at least 20: 1, as measured by X-ray photoelectron spectroscopy. 264. The method according to claim 263, further characterized in that the N- (phosphonomethyl) iminodiacetic acid, or a salt thereof, is contacted with the oxidation catalyst in the presence of oxygen in a continuous reactor system. 265. The method according to claim 263, further characterized in that the reducing medium comprises ammonia. 266. The method according to claim 263, further characterized in that the reducing agent comprises NaBH4. 267. A process for the preparation of N- (phosphonomethyl) glycine, or a salt thereof, comprising contacting, in the presence of oxygen, N- (phosphonomethyl) iminodiacetic acid, or a salt thereof, with a catalyst comprising a carbon support having a noble metal, a promoter, carbon and oxygen on a surface of the carbon support. 268. The method according to claim 267, further characterized in that it is carried out in a continuous reactor system. 269. The method according to claim 267, further characterized in that at least 0.05% by weight of the catalyst consists of at least one promoter. 270. - The method according to claim 267, further characterized in that the promoter is more easily oxidized than the noble metal. 271. The method according to claim 267, further characterized in that the promoter comprises a metal selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 272. The method according to claim 267, further characterized in that the promoter comprises tin. 273. The method according to claim 267, further characterized in that the promoter comprises iron. 274. The method according to claim 267, further characterized in that the promoter comprises titanium. 275. The method according to claim 267, further characterized in that there are at least two promoters on the surface of the carbon support, each of said promoters constituting at least 0.05% by weight of the catalyst. 276. The method according to claim 275, further characterized in that the promoters comprise iron and tin. 277.- The method according to claim 267, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 278. - The method according to claim 267, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 279. The method according to claim 267, further characterized in that substantially all the noble metal atoms on the surface are alloyed with the promoter. 280.- The method according to claim 267, further characterized in that the catalyst has a ratio of carbon atoms to oxygen atoms on the surface, which is at least about 20: 1, as measured by X-ray photoelectron spectroscopy after heating the catalyst to a temperature of about 500 ° C for about 1 hour in a hydrogen atmosphere, and before exposing the catalyst to an oxidant after heating in the hydrogen atmosphere. 281. The method according to claim 280, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 30: 1. 282. The method according to claim 280, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 40: 1. 283. The method according to claim 280, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 50: 1. 284. - The method according to claim 280, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 60: 1. 285. The process according to claim 280, further characterized in that the catalyst has a ratio of oxygen atoms to noble metal atoms on the surface, which is less than about 8: 1 after heating the catalyst to a temperature of about 500 ° C for about 1 hour in a hydrogen atmosphere, and before exposing the catalyst to an oxidant after heating in the hydrogen atmosphere. 286. The method according to claim 285, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 7: 1. 287. The method according to claim 285, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 6: 1. 288. The method according to claim 285, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 5: 1. 289.- The procedure according to claim 267, further characterized in that the catalyst produces no more than about 1.2 mmoles of carbon monoxide per gram of catalyst when a dry sample of the catalyst, after having been heated to a temperature of about 500 ° C for about 1 hour in a hydrogen atmosphere , and before being exposed to an oxidant after heating in the hydrogen atmosphere, is heated in a helium atmosphere at a temperature of about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for about 30 minutes. 290. The process according to claim 289, further characterized in that the production of carbon monoxide is not greater than about 0.7 mmole of carbon monoxide per gram of catalyst. 291. The process according to claim 289, further characterized in that the production of carbon monoxide is not greater than about 0.5 mmol of carbon monoxide per gram of catalyst. 292. The process according to claim 289, further characterized in that the production of carbon monoxide is not greater than about 0.3 mmole of carbon monoxide per gram of catalyst. 293. The catalyst according to claim 1, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst. 294. - The catalyst according to claim 13, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst. 295. The catalyst according to claim 30, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst. 296. The catalyst according to claim 48, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst, 297.- The catalyst according to claim 70, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst. 298. The method according to claim 83, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst. 299. The method according to claim 107, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst. 300.- The method according to claim 129, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst. 301. - The method according to claim 146, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst. 302. The method according to claim 165, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst. 303. An oxidation catalyst characterized in that it comprises a carbon support having on its surface: a noble metal and: (a) titanium, wherein the titanium constitutes at least 0.05% by weight of the catalyst, or (b) iron and tin, wherein the iron and tin each constitute at least 0.05% by weight of the catalyst. 304. The oxidation catalyst according to claim 303, further characterized in that the catalyst comprises a carbon support having on its surface: a noble metal; and titanium, wherein the titanium constitutes at least 0.05% by weight of the catalyst. 305. The oxidation catalyst according to claim 303, further characterized in that the catalyst comprises a carbon support having on its surface: a noble metal; and iron and tin, wherein the iron and tin each constitute at least 0.05% by weight of the catalyst. 306. The oxidation catalyst according to claim 303, further characterized in that the noble metal constitutes from about 0.5 to about 20% by weight of the catalyst. 307. - The oxidation catalyst according to claim 303, further characterized in that the noble metal constitutes no more than about 7.5% by weight of the catalyst. 308. A process for the preparation of a product comprising N- (phosphonomethyl) glycine, or a salt thereof, by oxidation of a substrate comprising N- (phosphonomethyl) iminodiacetic acid, or a salt thereof; characterized in that it comprises: continuously contacting an aqueous feed mixture comprising said substrate, with an oxidizing agent in the presence of a heterogeneous particulate catalyst for the reaction, in a continuous reaction system comprising a stirred reactor tank, thus producing a mixture of products comprising said product; separating the particulate catalyst from the product mixture by filtration, thereby producing a product filtrate comprising said product; and recovering said product from the product filtrate. 309.- The method according to claim 308, further characterized in that the substrate is contacted with an oxidizing agent in the presence of a catalyst effective to oxidize formaldehyde to carbon dioxide and water. 310. The process according to claim 309, further characterized in that it comprises contacting said substrate with an oxidizing agent in the presence of a catalyst that is effective, both for the oxidation of said substrate and for the oxidation of formaldehyde. 311. - The method according to claim 310, further characterized in that said product mixture does not contain more than about 2.4% by weight of formaldehyde. 312. The method according to claim 311, further characterized in that said product mixture contains no more than about 1.4% by weight of formaldehyde. 313. The process according to claim 312, further characterized in that said product mixture contains at least about 5% by weight of said product and no more than about 0.5% by weight of formaldehyde. 314. The method according to claim 313, further characterized in that said catalyst for the oxidation of formaldehyde comprises a noble metal on a carbon support, said catalyst being resistant to the dissolution of noble metal in the product mixture so that, at a 95% conversion of said substrate into said product, the degree of noble metal dissolution in the aqueous reaction mixture is not greater than about 5.3 g / g of N- (phosphonomethyl) glycine produced in the reaction. - The process according to claim 314, further characterized in that the resistance of the catalyst to the noble metal solution is such that the degree of dissolution of noble metal in said product mixture is less than about 1.0 μg / g of said product produced in the reaction. 316. - The method according to claim 315, further characterized in that the concentration of said product in said product mixture is from about 5% to about 40% by weight. 317.- The method according to claim 316, further characterized in that the concentration of said product in said product mixture is from about 8% to about 30% by weight. 318.- The method according to claim 317, further characterized in that said product mixture contains at least about 9% by weight of said product, and no more than about 0.5% by weight of formaldehyde. 319. The method according to claim 318, further characterized in that the concentration of said product in said product mixture is from about 9% to about 15% by weight. 320. The process according to claim 319, further characterized in that said noble metal comprises platinum, and the platinum content of said product mixture is less than about 1.0 μg / g of product produced in the reaction. 321. The method according to claim 320, further characterized in that said oxidizing agent comprises molecular oxygen. 322. - The method according to claim 321, further characterized in that the formaldehyde content of said product mixture is not greater than about 0.3% by weight. 323. The method according to claim 322, further characterized in that the substrate content of the product mixture is not greater than about 0.44% by weight. 324. The method according to claim 321, further characterized in that the substrate content of the product mixture is at least about 0.08% by weight. 325.- The method according to claim 324, further characterized in that it comprises: contacting with oxygen a first aqueous reaction medium comprising said substrate to produce said product and formaldehyde; and contacting with oxygen another aqueous reaction mixture containing said product, formic acid and formaldehyde produced in said first aqueous reaction mixture to oxidize formaldehyde, producing said product mixture. 326. The process according to claim 325, further characterized in that said oxidizing agent is molecular oxygen that is introduced separately into said first aqueous reaction medium and into said other aqueous reaction medium. 327.- The procedure according to claim 326, further characterized in that said other aqueous medium comprises unreacted substrate remaining in said first aqueous reaction medium, the process further comprising oxidizing substrate in said other reaction medium to produce additional product. 328.- The method according to claim 327, further characterized in that said first aqueous reaction medium is contacted with said oxidizing agent in a first reaction zone, and said other reaction medium is contacted with said oxidizing agent in another reaction zone, the oxidation of substrate and formaldehyde is carried out continuously in each of said reaction zones. 329. The method according to claim 328, further characterized in that each of said reaction zones comprises a stirred reactor tank. 330. The method according to claim 329, further characterized in that the conversion of substrate to product in said first continuous reaction zone is at least about 75%. 331. The method according to claim 330, further characterized in that the conversion of substrate to product in said first continuous reaction zone is at least about 80%. 332. The method according to claim 331, further characterized in that the oxygen feed rate in said other reaction zone is lower than the oxygen feed rate in said first reaction zone. 333. - The method according to claim 332, further characterized in that the oxygen feed rate for said first reaction zone is greater than about 0.4 l / (kg reaction medium) (min), and the feed rate of oxygen for said other reaction zone, is greater than about 0.19 l / (kg of reaction medium) (min). 334. The method according to claim 332, further characterized in that the oxygen feed rates for the two reaction zones are such that the total oxygen feed rate consumed in the process reactions is at least approximately 40%. 335. The method according to claim 334, further characterized in that the oxygen feed rates are such that the proportion of oxygen feed consumed in the reactions of the process is at least about 60%. 336. The method according to claim 335, further characterized in that the oxygen feed rates are such that the proportion of oxygen feed consumed in the process reactions is from about 60% to about 80%. 337. The method according to claim 335, further characterized in that the oxygen feed rates are such that the proportion of oxygen feed consumed in the reactions of the process is at least about 80%. 338. The method according to claim 337, further characterized in that the oxygen feed rates are such that the proportion of oxygen feed consumed in the reactions of the process is at least about 90%. 339. The process according to claim 336, further characterized in that the pH of the aqueous reaction mixture in each of the reaction zones is less than about 3. 340. The process according to claim 339, further characterized in that the pH of the aqueous mixture in each of the reaction zones is from about 1 to about 2. 341. The method according to claim 340, further characterized in that the total residence time in the first and in the other reaction zone is from about 3 to about 120 minutes. 342. The method according to claim 341, further characterized in that the total residence time in the first and in the other reaction zone is from about 5 to about 90 minutes. 343. The method according to claim 342, further characterized in that the total residence time in the first and in the other reaction zone is from about 5 to about 60 minutes. 344. The method according to claim 343, further characterized in that the residence time in the other reaction zone is from about 2 to about 40 minutes. 345. The method according to claim 344, further characterized in that the residence time in the other reaction zone is from about 5 to about 20 minutes. 346. The method according to claim 345, further characterized in that the residence time in the other reaction zone is from about 5 to about 15 minutes. 347.- The method according to claim 346, further characterized in that the temperature in the other reaction zone remains equal to or lower than the temperature in said first reaction zone, and the pressure in the other reaction zone is maintained equal to or less than the pressure in said first reaction zone. 348. The method according to claim 347, further characterized in that the reduced oxygen feed rate in the other reaction zone is effective to produce a minor proportion of aminomethylphosphonic acid byproduct from that which could be produced under otherwise identical, except for the reduced oxygen feed rate in the other reaction zone. 349. - The method according to claim 348, further characterized in that the concentration of formaldehyde in said product mixture is less than about 0.15% by weight. 350. The process according to claim 348, further characterized in that the catalyst is recycled to the reaction system for further use in the oxidation of substrate and formaldehyde, said reaction system comprising said first reaction zone and said other zone of reaction. 351. The method according to claim 350, further characterized in that product of the filtrate obtained by filtering the product mixture for removal of the catalyst is recovered. 352. The method according to claim 351, further characterized in that a sacrificial reducing agent is introduced into the reaction system comprised of said first reaction zone and said other reaction zone, the sacrificial reducing agent being effective to maintain the catalyst in a reduced state. 353. The method according to claim 352, further characterized in that the formaldehyde produced in said reactor system is recycled to said reactor system. 354. The process according to claim 353, further characterized in that formic acid and formaldehyde are removed that did not react from the product mixture leaving said other reaction zone and recycled to said reaction system as a source of said sacrificial reducing agent. 355. The process according to claim 354, further characterized in that said catalyst contains at least about 0.05% by weight of promoter, based on the total catalyst. 356. The method according to claim 355, further characterized in that said promoter is selected from the group consisting of tin, bismuth, lead, cadmium, magnesium, manganese, nickel, aluminum, cobalt, titanium, antimony, selenium, iron, rhenium, cerium, zinc and zirconium. 357. The method according to claim 356, further characterized in that said promoter is selected from the group consisting of iron, bismuth and titanium. 358. The method according to claim 357, further characterized in that the total content of the promoter does not constitute more than about 10% by weight of the catalyst. 359. The method according to claim 358, further characterized in that the total content of the promoter constitutes approximately 0.1% to about 2% by weight of the catalyst. 360. The method according to claim 359, further characterized in that the total content of the promoter constitutes approximately 0.2% to approximately 1.5% by weight of the catalyst. 361. The method according to claim 358, further characterized in that before said oxidation of said substrate, the catalyst produces no more than about 1.2 mmole of carbon monoxide per gram of catalyst when a dry sample of the catalyst is heated in a helium atmosphere at a temperature of about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for about 30 minutes. 362. The method according to claim 361, further characterized in that before said oxidation of said substrate, the catalyst produces no more than about 0.7 mmoles of carbon monoxide per gram of catalyst when a dry sample of the catalyst is heated in a helium atmosphere at a temperature of about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then at a temperature of about 900 ° C for about 30 minutes. 363. The method according to claim 362, further characterized in that before said oxidation of said substrate, the catalyst produces no more than about 0.5 mmol of carbon monoxide per gram of catalyst when a dry sample of the catalyst in an atmosphere of helium is heated to a temperature of about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then to a temperature of about 900 ° C for about 30 minutes. 364. - The method according to claim 363, further characterized in that, prior to said oxidation of said substrate, the catalyst produces no more than about 0.3 mmoles of carbon monoxide per gram of catalyst when a dry sample of the catalyst in a helium atmosphere it is heated to a temperature of about 20 to about 900 ° C, at a rate of about 10 ° C per minute, and then to a temperature of about 900 ° C for about 30 minutes. 365. The method according to claim 362, further characterized in that the carbon support has a specific surface area of about 10 to about 3000 m2 / g, as measured by the Brunauer-Emmett-Teller method. 366. The method according to claim 365, further characterized in that: the catalyst comprises a carbon support having a noble metal, a promoter, carbon and oxygen on a surface of the non-graphitic carbon support; wherein, prior to said oxidation of said substrate, the catalyst has a ratio of carbon atoms to oxygen atoms of at least about 20: 1 on the surface, as measured by X-ray photoelectron spectroscopy; and wherein the carbon support has a specific surface area of from about 10 to about 3000 m2 / g, as measured by the Brunauer-Emmett-Teller method. 367. - The method according to claim 366, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 30: 1. 368. The method according to claim 367, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 40: 1. 369. The method according to claim 368, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 50: 1. 370. The method according to claim 369, further characterized in that said ratio of carbon atoms to oxygen atoms is at least about 60: 1. 371. The method according to claim 367, further characterized in that the promoter is oxidized more easily than the noble metal. 372. The method according to claim 371, further characterized in that said catalyst is prepared by means of a process comprising depositing a noble metal on a surface of said carbon support, and then heating the surface to a temperature greater than 500 ° C. 373. The method according to claim 372, further characterized in that said surface is heated to a temperature of about 550 to about 1200 ° C. 374. - The method according to claim 373, further characterized in that said surface is heated to a temperature of about 550 to about 900 ° C. 375. The method according to claim 374, further characterized in that said heating of the surface of the support at a temperature greater than 500 ° C is carried out in the presence of a gas selected from the group consisting of N2, a noble gas, H2, ammonia and carbon monoxide. 376. The method according to claim 373, further characterized in that, before the deposition of the noble metal, the carbon support has carbon and oxygen on its surface in amounts such that the ratio of carbon atoms to oxygen atoms in the surface is at least about 20: 1, as measured by X-ray photoelectron spectroscopy. 377. The method according to claim 376, further characterized in that the noble metal atoms on the surface are alloyed with the promoter. 378. The method according to claim 377, further characterized in that a majority of the noble metal atoms on the surface are alloyed with the promoter. 379. The method according to claim 378, further characterized in that substantially all of the noble metal atoms on the surface are alloyed with the promoter. 380. - The method according to claim 377, further characterized in that the promoter comprises tin. 381. The method according to claim 377, further characterized in that the promoter comprises iron. 382. The method according to claim 377, further characterized in that the promoter comprises titanium. 383. The method according to claim 377, further characterized in that the promoter comprises bismuth. 384. The method according to claim 377, further characterized in that the catalyst comprises two promoters on the surface of the carbon support, each of said promoters constituting at least 0.05% by weight of the catalyst. 385. The method according to claim 384, further characterized in that the promoters comprise iron and a second promoter selected from the group consisting of tin, titanium and bismuth. 386. The method according to claim 377, further characterized in that said catalyst comprises a particulate carbon support in which at least about 95% of the particles are from about 2 to about 300 μm in their largest dimension. 387.- The method according to claim 386, further characterized in that said catalyst comprises a particulate carbon support in which at least about 98% of the particles are from about 2 to about 200 μm in their largest dimension. 388.- The method according to claim 386, further characterized in that the Brunauer-Emmett-Teller surface area of said carbon support is from about 500 to about 3000 m2 / g. 389.- The method according to claim 388, further characterized in that the Brunauer-Emmett-Teller surface area of said carbon support is from about 750 to about 2100 m2 / g. 390. The method according to claim 389, further characterized in that the Brunauer-Emmett-Teller surface area of said carbon support is from about 750 to about 1750 m2 / g. 391. The method according to claim 388, further characterized in that the pore volume of said carbon support is from about 0.1 to about 2.5 ml / g. 392. The method according to claim 391, further characterized in that the pore volume of said carbon support is from about 0.2 to about 2.0 ml / g. 393. The method according to claim 392, further characterized in that the pore volume of said carbon support is from about 0.4 to about 1.7 ml / g. 394. - The method according to claim 388, further characterized in that the concentration of noble metal deposited on the surface of the carbon support is from about 0.5% to about 20% by weight of the catalyst. 395. The method according to claim 394, further characterized in that the concentration of noble metal deposited on the surface of the carbon support is from about 2.5% to about 10% by weight of the catalyst. 396. The method according to claim 395, further characterized in that the concentration of noble metal deposited on the surface of the carbon support is from about 3% to about 7% by weight of the catalyst. 397. The method according to claim 395, further characterized in that the dispersion of noble metal deposited on the surface of the carbon support is such that the concentration of noble metal surface atoms is from about 10 to about 400 moles / g. , measured by hydrogen chemosorption using an instrument Micromeritics ASAP 2010C or Altamira AMI100. 398. The method according to claim 397, further characterized in that the noble metal dispersion is such that the concentration of the noble metal surface atoms is from about 10 to about 150 μmoles / g. 399. The process according to claim 395, further characterized in that the surface concentration of the noble metal atoms is from about 15 to about 100 μmoles. 400.- The method according to claim 395, further characterized in that the noble metal is on the surface of the carbon support in the form of metal particles and at least about 90% (numerical density) of the noble metal particles on the surface of the carbon support are from about 0.5 to about 35 nm in its largest dimension. 401. The method according to claim 400, further characterized in that at least about 90% (numerical density) of the noble metal particles are from about 1 to about 20 nm in their largest dimension. 402. The method according to claim 401, further characterized in that at least about 90% (numerical density) of the noble metal particles are from about 1.5 to about 10 nm in their largest dimension. 403. The method according to claim 401, further characterized in that at least about 80% of the noble metal particles are from about 1.5 to about 7 nm in their largest dimension. 404. - The method according to claim 403, further characterized in that said catalyst contains about 0.1% to about 2% iron. 405. The method according to claim 404, further characterized in that, prior to said oxidation of said substrate, the catalyst has a ratio of oxygen atoms to noble metal atoms on the surface that is less than 7: 1, as measured by X-ray photoelectron spectroscopy. The method according to claim 405, further characterized in that said ratio of oxygen atoms to noble metal atoms on the surface of said catalyst is less than about 6: 1. 407. The method according to claim 406, further characterized in that said ratio of oxygen atoms to noble metal atoms is less than about 5: 1. 408. The method according to claim 404, further characterized in that N- (phosphonomethyl) glycine is recovered from the filtrate by precipitation. 409. The process according to claim 408, further characterized in that N- (phosphonomethyl) glycine is recovered by evaporation of a portion of the water contained in the filtrate, to produce a more concentrated solution of N- (phosphonomethyl) glycine, and the more concentrated solution is cooled to crystallize the N- (phosphonomethyl) glycine. 410. The process according to claim 409, further characterized in that the catalyst is also effective for the oxidation of formic acid, and the formic acid produced in the reactor system is also oxidized there.