MXPA00012882A - Catalytic partial oxidation with two catalytically-active metals - Google Patents

Abstract

The invention relates to a catalyst or a precursor thereof in the form of a fixed arrangement or in the form of catalyst (precursor) particles, wherein the fixed arrangement or the particles comprise(s) at least two layers, the first layer comprising as a catalytically active metal or precursor thereof rhodium or a rhodium compound and the second layer comprising as a catalytically active metal or precursor thereof iridium, osmium or platinum or a compound thereof. The invention further relates to the use of the catalyst, especially in a process for the catalytic partial oxidation of a hydrocarbonaceous feedstock.

Description

CATALYTIC PARTIAL OXIDATION WITH TWO CATALYTICALLY ACTIVE METALS Field of Invention The present invention relates to a catalyst or a precursor of this catalyst in the form of a fixed distribution or in the form of particles of a catalyst (precursor), and is related to the use of the catalyst, especially in a process for partial catalytic oxidation of a hydrocarbon feedstock.

Background of the Invention.

The partial oxidation of hydrocarbons, for example methane or natural gas, in the presence of a catalyst constitutes an attractive route for preparing mixtures of carbon monoxide and hydrogen which are known in the art as synthesis gas. The partial oxidation of a hydrocarbon is an exothermic reaction and, in the case where the methane is the hydrocarbon, it is carried out with the next reaction: Ref: 125932 2CH4 + O; 2C0 + 4 H: A mixture of carbon monoxide and hydrogen prepared with this process is particularly suitable for use in the synthesis of hydrocarbons, for example by means of Fischer-Tropsch synthesis, or the synthesis of oxygenates, such as for example methanol. Processes for the conversion of the mixture of monoxide and hydrogen into such products are well known in the art.

Hydrogen, or a mixture of hydrogen with other gases prepared with this process may be particularly suitable for use as a combustible product either directly or indirectly.

The partial catalytic oxidation process could be used in a very appropriate manner to produce the hydrogen feed for a fuel cell. In the fuel cells, hydrogen and oxygen are passed over the fuel cell in order to produce electricity and water. Fuel cell technology is well known in the art.

In order to obtain large productions of carbon monoxide and hydrogen, it is preferred, for thermodynamic reasons, that the partial oxidation process be operated at relatively high temperatures.

The literature contains several documents that reveal the details of the experiments that relate to the catalytic oxidation of hydrocarbons, particularly methane, using a wide range of catalysts. Reference is cited, for example, to U.S. Patent 5 149 464 and WO 92/11199.

To be commercially attractive, a partial catalytic oxidation process should be able to operate under relatively severe conditions, i.e. the combination of an elevated temperature and a high space velocity per hour of the gas. An important factor when considering a catalyst for its application in a commercial process, is the catalyst stability under the predominant conditions in the process.

EPA-A-0 629 578 discloses that at a temperature of at least 950 ° C and at a very high space velocity per hour of the gas, there is a marked difference in the stability of group VIII metal catalysts. It has been observed that catalysts comprising rhodium, iridium or ruthenium exhibit a significantly higher stability in relation to both selectivity and activity than the other group VIII metal catalysts.

U.S. Patent 5,648,582 relates to a partial catalytic oxidation process at very high space velocity per hour and at a catalyst temperature in the boundary zone from 850 ° C to 1150 ° C using a catalyst comprising rhodium, nickel , or platinum.

WO 97/37929 is related to the equipment for carrying out partial catalytic oxidation reactions. It is mentioned that a catalyst bed having a first layer comprising rhodium and a second layer comprising ruthenium or nickel can be used, in order to reduce the amount of rhodium.

Although ruthenium and nickel are relatively inexpensive materials, and therefore attractive for use as catalytically active metals, a major disadvantage of the use of ruthenium or nickel in partial catalytic oxidation lies, however, in that a relatively large amount is formed. large traces of undesirable components such as ammonia and hydrogen cyanide.

In WO 95/18063, for example, it is disclosed that partial oxidation catalysts comprising rhodium, iridium or platinum as the catalytically active metal, generate significantly lower amounts of ammonia and hydrogen cyanide than catalysts comprising other catalytically active metals. . It is demonstrated in the examples that a ruthenium-containing catalyst generates a relatively large amount of ammonia and hydrogen cyanide.

In GB 2 274 284, a catalytic partial oxidation process using a catalyst distributed as a plurality of catalytic beds in cascade for each other is described. In order to create a plurality of adiabatic layers, the heat is removed between the catalyst beds or cold streams of the reactants are introduced between the beds. In a preferred embodiment, the catalyst of the first The catalytic bed comprises rhodium in association with platinum or palladium and the catalyst (s) of the subsequent catalytic bed contains two metals selected from rhodium, ruthenium and iridium.

There is still a problem in the art that catalysts comprising either rhodium or iridium are slowly deactivated under the severe process conditions that are required for commercial operation in order to produce the mixtures of carbon monoxide and hydrogen.

Description of the invention.

Surprisingly, it has now been found that the stability of a catalyst can Increase by using a combination of two catalytically active metals in two different layers. In particular, it has been found that a catalyst in the form of a fixed distribution, wherein a first layer comprises rhodium as the catalytically active metal and a second layer comprises iridium, osmium or platinum as the catalytically active metal, exhibits a speed of slower deactivation than a catalyst comprising rhodium, iridium, osmium or platinum as the catalytically active metal.

Therefore, the present invention relates to a catalyst or a precursor of this catalyst in the form of a fixed distribution, wherein the fixed distribution comprises a first layer which, during normal operation, is located at the upstream end of the distributed catalyst and comprises as the catalytically active metal or precursor thereof, rhodium or a rhodium compound and a second layer adjacent to the first layer without space between the first and second layer, which is, during normal operation, located downstream of the first layer, the second The layer comprises, as the catalytically active metal or precursor thereof, iridium, osmium or platinum or a compound thereof.

When referring to a first layer, it refers to a layer that is, under operating conditions, located at the upstream end of the fixed distribution. The second layer is then located (under operating conditions) under the first layer, appropriately adjacent to the first layer. There is no separation between the first and the second layer. The fixed distribution may contain more than two layers, but a two-layer distribution is preferred.

The fixed distribution may have any suitable shape, provided that the distribution is permeable to a fluid, especially gas. The fixed distribution suitably has an empty fraction in the boundary range of 0.4 to 0.95, preferably in the boundary range of 0.6 to 0.9. Examples of the appropriate fixed distributions are a fixed bed of catalyst carrier particles, such as refractory oxide particles, a distribution of wires or gauzes of a carrier material of metal catalysts, or a porous, metal or ceramic monolithic structure, such as a honeycomb of a foam, or combinations of these examples. The fixed distribution can also have the form of wires or gauzes of the catalytically active metal.

The fixed distribution of the present invention may have the form of at least one porous monolithic structure. With reference herein to porous, it refers to any individual unit of porous material, such as, for example, a unit of a refractory material wherein the pores comprise straight or twisted, parallel or randomly elongated channels extending through the structure of the porous material. the unit, that is, they have an interconnected open porosity. By referring to the pores, it refers to the openings or spaces between adjacent portions or regions of the monolithic structure. Therefore, it will be appreciated that the pores mentioned in connection with the present invention possess a nominal diameter in the order of magnitude from 0.05 mm to 5 mm.

These pores should be interpreted as a contrast to smaller pores, including micropores and mesopores that may be present in the catalyst support material itself.

The porous monolithic structure can have any suitable shape. One form of the porous monolithic structure is that of a honeycomb. The honeycombs are characterized by having a plurality of straight and elongated straight channels extending through the structure. Preferred porous monolithic structures are foams, more preferably ceramic foams. Suitable ceramic foams are commercially available, for example in Selee In. , Hi-Tech and Dytech. Preferred ceramic foams have a number of pores per cm in the boundary range from 10 pores per cm to 120 pores per cm, more preferably in the boundary range from 20 pores per cm to 80 pores per cm.

Suitable materials as catalyst carriers are well known in the art and include refractory oxides, such as silica, alumina, titanium, zirconium and mixtures thereof, and metals. Strong alloy steels containing alumina, such as feck alloy type materials, are particularly suitable metals. The preferred refractory oxides are based on zirconium, more preferably comprising at least 70% by weight zirconium, for example selected from known forms of stabilized (partially) zirconium or substantially pure zirconium. The most preferred zirconium based materials of all comprise zirconium stabilized or partially stabilized with one or more oxides of Mg, Ca, Al, Y, La or Ce. The most suitable carrier materials of all are Ce-ZTA (alumina hardened with zirconium) and Y-PSZ (partially stabilized zirconium) which are both commercially available.

The fixed distribution can be of any form. Appropriately, the end downstream of the fixed distribution is co-planar with respect to the upstream end.

The fixed distribution can be composed of different structures, for example a metal gauze as the first layer and a ceramic foam as the second layer.

If the fixed distribution is in the form of a fixed bed of catalyst particles, the bed appropriately contains, on its upstream side, a first layer filled with catalyst particles (precursor) comprising rhodium or a rhodium compound as the catalytically active metal (precursor) and, on the downstream side of the first layer, adjacent to the first layer, a second layer filled with particles comprising iridium, osmium or platinum or a compound of these metals, such as metal catalytically active (precursor).

The present invention is further related to a catalyst or catalyst precursor in the form of catalyst particles (precursor) comprising a first outer layer comprising as a catalytically active metal or a precursor of a catalytically active metal, rhodium or a rhodium compound and a second layer comprising as a catalytically active metal or a precursor of a catalytically active metal, iridium, osmium or platinum or a compound of these metals. These catalyst particles can be used in either a fixed bed of particles or in a fluidized bed regime. Suitably, the catalyst particles (precursor) of the present invention are catalyst carrier particles, such as refractory oxide particles, impregnated with the catalytically active metals (precursors).

Preferably, the second catalyst layer of the present invention comprises iridium or an iridium compound such as the catalytically active metal or the precursor of the catalytically active metal.

Each catalyst layer can comprise the catalytically active metal in any appropriate amount to obtain the required level of activity. In the case of a fixed distribution, the catalytically active metal of at least one of the layers may be present in the form of wires or gauzes of the catalytically active metal. Preferably, the catalytically active metals are supported on a catalyst carrier material.

Typically, each catalyst layer comprises the active metal in a concentration in the boundary range from 0.02 wt% to 10 wt%, more preferably from 0.1 wt% to 7.5 wt% based on the weight of the carrier material. The concentration of metal is typically constant throughout the length and width of each layer. Optionally, the first layer may also comprise the catalytically active metal of the second layer, i.e., iridium, osmium or platinum in addition to the rhodium.

In an alternative embodiment of the fixed distribution of the present invention, the concentration of the catalytically active metal of the first layer, i.e., rhodium, decreases gradually in a direction of the fixed distribution and the concentration of the catalytically active metal of the second layer, that is, iridium, osmium B ^ < ^ ¿_M. Sfci & or platinum, decreases gradually in the other direction of the fixed distribution.

Typically, the amount by weight of the catalytically active metal in the first layer, preferably, the amount of the catalytically active metal in the second layer is greater than the amount in the first layer. More preferably, the second layer comprises at least twice the amount of the first layer, still more preferably, at least three times that amount. The amount in the second layer is at most 50 times the amount in the first layer, preferably, at most 20 times that amount.

It has been found that the catalyst of the present invention can be further improved by adding platinum to the first layer. The addition of platinum minimizes the risk that during the start-up of the partial catalytic oxidation process, a wear of the catalyst in the second layer will occur. A wear in the second layer would produce an accelerated deactivation of the catalyst. The addition of platinum is especially convenient in those applications where start-up occurs frequently, for example in automotive applications, or in those catalysts where the amount of rhodium in the first layer compared to the amount of iridium in the second layer it is relatively low. This can easily happen if the catalyst has the form of a fixed distribution where The first layer has a less dense structure than the second layer, such as for example that a first layer comprises a distribution of metallic wire or gauze and a second layer comprising a ceramic foam.

Preferably, the weight ratio of rhodium to platinum in the first layer is in the boundary range of 1 to 20, preferably 5 to 15. 20 The catalyst carrier material can be impregnated with the catalytically active metals or with the precursors of these catalytically active metals through processes known in the art. The appropriate processes they are the impregnation or the washing coating of the catalytic carrier material with the catalytically active material or a precursor of this material. The impregnation typically comprises contacting the carrier material with a solution of a compound of the catalytically active material or the precursor of this catalytically active material, followed by drying and, optionally, by calcining the resulting material. If more than one catalytically active material or precursor of this catalytically active material is to be impregnated, co-impregnation or sequential impregnation can be applied.

In the case of a fixed distribution comprising a porous monolithic structure, the structure can be impregnated sequentially or coated by washing with two different solutions, or each containing a different compound or different catalytically active metal compounds. The layer that should not be impregnated can be supplemented with a wax or other material that prevents impregnation. As an alternative, the Structure can be partially submerged during impregnation or coating by washing.

The catalyst particles comprising a first rhodium-containing outer layer and a second layer containing iridium, osmium or platinum can be prepared by means of impregnation or washing coating with the catalytically active metal compound of the second layer, followed by an impregnation or coating by washing with the compound or compounds of the catalytically active metal or the catalytically active metals of the first layer.

The catalytically active metal or the precursor of this catalytically active metal in at least one of the layers may be associated with at least one inorganic metal cation or a precursor of this inorganic metal cation such that the inorganic metal cation is present in association intimate, supported on or with the catalytically active metal, as described in International Patent Application PCT / EP99 / 00324.

The cation is selected from Groups IIA, IIIA, IIIB, IVA and IVB of the Periodic Table of the Elements and the lanthanides for example al, Mg, Zr, Ti, La, Hf, Si and Ba, where Zr is preferred. The cation preferably has the form of its oxide.

When referring to the intimate association of the cation, it refers to its incorporation in an appropriate way on or with the metal, thus modifying the catalytic performance properties of this metal.

Therefore, the intimate association of the cation with the catalytically active metal is suitably produced at the surface of the catalyst. Preferably, the catalyst comprises a cation to metal ratio in excess of or equal to 1.0 on its surface, more preferably in excess of or equal to 2.0, still more preferably in excess of equal to 3.0 to a maximum limited only by the limitations of the method to build the catalyst, such as impregnation.

The catalytically active metal is present in an essential way as an intimate aggregate mixture with the metal cation or as layers that resemble an aggregate mixture. Preferably, the aggregate mixture is present substantially as a single layer or as separate clusters. The aggregate mixture may be present throughout the length and width of the catalyst bed or may be present only in some regions of the catalyst bed, such as at the upper edge of a fixed bed.

The thickness of a layer of the metal cation as defined above can be selected in order to obtain an optimum effect and can be determined with the measurement of the reaction selectivity and similar parameters. The thickness is conveniently in the order of microns.

The present invention relates additionally to a process for the partial catalytic oxidation of a hydrocarbon feedstock, wherein the process comprises contacting a feedstock comprising a hydrocarbon feedstock and an oxygen-containing gas with a hydrocarbon feedstock. catalyst in the form of a fixed distribution or in the form of catalyst particles as defined above, preferably at a pressure in the boundary range from 1 bar to 150 bar, at a temperature in the boundary range from 750 ° C to 1400 ° C, and with a space velocity per hour of the gas in the limit zone from 20,000 to 100,000,000 Nl / kg / h. When referring to the temperature, it refers to the temperature of the gas leaving the catalyst.

The hydrocarbon feedstock is in the gas phase when it is contacted with the catalyst. The feedstock may contain compounds that are gaseous under standard conditions of temperature and pressure (ie, at 0 ° C and 1 atmosphere).

The process is particularly appropriate for the partial oxidation of methane, natural gas, associated gas or other sources of light hydrocarbons. In this sense, the term "light hydrocarbons" refers to the The process can be conveniently applied in the conversion of gas from natural methane reserves containing substantial amounts of carbon dioxide. preferably methane in an amount of at least 50% by volume, preferably at least 70% by volume, especially at least 80% by volume.

The process is also suitable for the conversion of feed charges that are gaseous when contacted with the catalyst during operation, but are liquid under standard conditions of temperature and pressure. Typically, these feedstocks have an average carbon number of at least 6 and contain up to 25 carbon atoms in their molecules. Examples of such feedstocks are hydrocarbons having a boiling point in the boundary range from 50 ° C to 500 ° C, preferably in the boundary range from 60 ° C to 350 ° C. The process is particularly appropriate for oxidation partial loading of naphtha feeds having a boiling point between 35 ° C and 150 ° C, documentation loads or synthetic diesel feed charges having a boiling point between 200 ° C and 500 ° C, in a manner particularly between 200 ° C and 300 ° C.

It is possible that the hydrocarbon material is present in the feed charges that are gaseous under standard conditions of temperature and pressure, together with the material that is liquid under standard conditions of temperature and pressure and that have an average carbon number of at least 6.

The process according to the present invention can also be carried out when the feedstock contains oxygenates (in gaseous state, and with less than 6 carbon atoms, and / or in liquid state under standard conditions of temperature and pressure and with a average carbon number of at least 6). The oxygenates to be used as (part of) the feedstock in the process according to the present invention are defined as molecules that contain in addition to the carbon and hydrogen atoms at least 1 oxygen atom that binds either with one or two carbon atoms with either a carbon atom and a hydrogen atom. Examples of suitable oxygenates comprise methanol, ethanol, dimethyl ether and similar oxygenates.

It is also possible to use the mixtures of the hydrocarbons and oxygenates as defined above as the feedstock in the process according to the present invention.

The hydrocarbon feedstock is contacted with the catalyst as a mixture with a gas containing oxygen. Appropriate gases that contain pure oxygen. The use of air as the oxygen-containing gas is preferred.

The feed mixture may optionally comprise steam. Also optionally, the feed mixture may comprise carbon dioxide in a concentration of up to 60% by volume of the total feed mixture, especially from 0.1% by volume to 40% by volume.

The hydrocarbon feedstock and the oxygen-containing gas are preferably present in the feed in amounts such that they produce an oxygen to carbon ratio in the boundary range from 0.3 to 0.8, more preferably in the limit zone from 0, 45 to 0.75. The references that are made to the proportion of oxygen in the form of molecules (02) with respect to the carbon atoms that are present in the hydrocarbon feed charge. The proportions of oxygen to carbon in the region of the stoichiometric ratio of 0.5, ie the proportions in the boundary range from 0.45 to 0.65, are especially related. If oxygenated feedstocks, such as methanol, are used, oxygen to carbon ratios of below 0.3 can be used appropriately. If steam is present in the feed, the vapor to carbon ratio is preferably in the boundary range from above 0.0 to 3.0, more preferably from 0.0 to 2.0. The hydrocarbon feedstock, the oxygen-containing gas and the vapor, if present, are preferably mixed thoroughly before being contacted with the heater. The feed mixture is preferably preheated before being contacted with the catalyst.

The feed is preferably contacted with the catalyst under adiabatic conditions. For the purposes of this specification, the term "adiabatic" refers to the reaction conditions under which substantially all heat and radiation losses from the reaction zone are prevented, with the exception of the heat leaving the gaseous effluent stream of the reactor. A substantial prevention of all heat losses refers to the fact that the heat losses are at most 1% of the net calorific value.

The optimum pressure, temperature and special speed per hour of the gas may vary with the scale and purpose of the partial catalytic oxidation process. In general, more severe conditions are applied, that is, higher pressure, temperature and space velocity, for the -? Jtega * ßA &-JS &j large-scale commercial production of synthesis gas, such as for use in the synthesis of Fischer-Tropsch hydrocarbons or for the synthesis of methanol for small-scale applications, such as the hydrogen supply for fuel cells.

The process of the present invention can be operated at any appropriate pressure. For large-scale applications, the most appropriate pressures of all are high pressures, that is, pressures that are significantly above atmospheric pressure. The process is preferably operated at pressures in the limit zone from 1 bar to 150 bar. More preferably, the process operates at pressures in the boundary zone from 2 bar up to 100 bar, especially from 5 bar to 50 bar.

Under the preferred high pressure conditions prevailing in the large-scale operated processes, the feed is preferably contacted with the catalyst at a temperature in the boundary range from 750 ° C to 1400 ° C, more preferably from 850 ° C to 1350 ° C, and even more preferably from 900 ° C to 1300 ° C.

The feed can be supplied during the operation of the process at any appropriate spatial velocity. An advantage of the process of the present invention is that it is possible to achieve very high spatial velocities of the gas. Therefore, the spatial velocities of the gas for the process (which are expressed in normal liters of gas per kilogram of catalyst per hour, where the term normal liters refers to liters under STP conditions, that is, 0 ° C and 1 atmospheres) are preferably found in the boundary zone from 20,000 Nl / kg / h to 100,000,000 Nl / kg / h, more preferably in the boundary range from 50,000 Nl / kg / h to 50,000,000 Nl / kg / h. The speeds in the boundary zone from 500,000 to 30,000,000 Nl / kg / h are particularly suitable for the process of the present invention.

The present invention is illustrated below in an additional manner by way of the following examples. Example 1 (comparative) Preparation of the catalyst A ceramic foam containing 25 pores per cm (65 ppi) was crushed and the particles from 0.17 mm to 0.55 mm (30 to 80 mesh fraction) were impregnated by immersion in an aqueous solution containing 7.8% by weight of rhodium (such as rhodium trichloride and 11.2% by weight zirconium (such as zirconium nitrate) The impregnated particles were dried at 140 ° C and then calcined at 700 ° C for 2 hours. The resulting catalyst particles (catalyst A) comprise 5% by weight of rhodium and 7% by weight of zirconium based on the total weight of the calcined catalyst particles.

Partial catalytic oxidation A reactor tube 6 mm in diameter was filled with an amount of 0.5 g of the catalyst particles containing rhodium and that & - * ~ you? -" "" " to", . were prepared as described above. A quantity of nitrogen (914 Nl / h), oxygen (440 Nl / h) was mixed thoroughly and preheated to a temperature of 300 ° C. The preheated mixture was fed to the reactor at a pressure of 11 bar. The methane conversion was monitored for 150 hours. The temperature of the gas leaving the catalyst bed ranged between 930 ° C and 950 ° C.

Example 2 (comparative) Preparation of the catalyst A ceramic foam containing 25 pores per cm (65 ppi) was crushed and the particles from 0.17 mm to 0.55 mm (30 to 80 mesh fraction) were impregnated by immersion in an aqueous solution of iridium chloride and zirconium nitrate. The resulting particles were dried at 140 ° C and then calcined at 700 ° C for 2 hours. The resulting catalyst particles comprised 5% by weight of rhodium and 7% by weight of zirconium based on the total weight of the calcined aliquot particles.

Partial catalytic oxidation A reactor tube 6 mm in diameter was filled with an amount of 0.5 g of the catcher particles containing iridium and which were prepared as described above. A partial catalytic oxidation experiment was carried out using the same procedure as described in example 1. The methane conversion was monitored for 150 hours. The temperature of the gas leaving the catalyst bed ranged between 930 ° C and 950 ° C.

Example 3 (according to the invention) Partial catalytic oxidation A 6 mm diameter reactor tube was filled with an amount of 0.1 g of the rhodium-containing catalyst particles on top of an amount of 0.4 g of the iridium-containing catalyst particles which were prepared as described above. A partial oxidation experiment was carried out using the same procedure as described in example 1. The * ~ m **? ~ • • aa «fefaft * .g < - A »t methane conversion was monitored for 250 hours. The temperature of the gas leaving the catalyst bed ranged between 930 ° C and 950 ° C.

Figure 1 illustrates the methane conversion versus the test time for examples 1 to 3 (indicated as 1.2 and 3, respectively) The X axis shows the hours above the current It is evident that the catalyst in the form of the fixed distribution of the invention (example 3) exhibits better stability (lower deactivation ratio) than catalysts containing either rhodium or iridium In a commercial operation, the difference observed in relation to stability means a significant improvement.

Example 4 Preparation of the catalyst A commercially available Fecralloy wire gauze (0.125 mm, ex Resistalloy, UK) was oxidized at 1100 ° C for 48 hours and then immersed with a zirconium paint. The coated gauze was impregnated by immersing it twice in an aqueous solution containing an amount of 7.4% by weight of Rh (such as rhodium trichloride), 0.62% by weight of Pt (as platinum of hexachloroplatinic acid), and , 1% by weight of Zr (as zirconium nitrate). After each immersion the gauze was dried at 140 ° C and calcined for 2 hours at 700 ° C. The resulting gauze comprised 1.7% by weight of Rh, 0.14% by weight of Pt and 2.6% by weight of Zr based on the total weight of the gauze.

A ceramic foam (Y-PSZ, ex Selee) containing 30 pores per cm (80 ppi) was impregnated with an aqueous solution containing iridium chloride and zirconium nitrate. The impregnated foam was dried at 140 ° C and then calcined at 700 ° C for 2 hours. The resulting foam comprised 5% by weight of Ir and 7% by weight of Zr based on the total weight of the foam.

A 12 mm diameter reactor tube was filled with an amount of 1.74 g of the RH / Pt / Zr gauze (first layer on top of an amount of 1.57 g of the Ir / Zr foam ( second layer) that was prepared as described above.

Partial catalytic oxidation A partial catalytic oxidation experiment was conducted in the following manner. A quantity of naphtha (306.5 g / h), steam (180 g / h), oxygen (220 Nl / h) and nitrogen (975 Nl / h) were thoroughly mixed and thoroughly mixed and preheated to a temperature of 200 ° C. This corresponds to an oxygen to carbon ratio of the feed mixture of 0.45, a steam to carbon ratio of 0.46, and a space velocity per hour of the gas of approximately 450,000 Nl / kg / h. The preheated mixture was fed to the catalyst at a pressure of 6 bar.

To put the partial catalytic oxidation process into operation, a small amount of hydrogen was added to the feed mixture. Approximately 30 minutes after the start-up, the naphtha conversation was determined. After one hour the process is finished. The measurements of start-up and conversion of naphtha were repeated twice. The results are illustrated in table 1.

Example 5 Catalyst Preparation A gauze coated with Fecra alloy was prepared in the same manner as in Example 4. The coated gauze was impregnated by immersing it twice in an aqueous solution containing 7.9% by weight of Rh (such as rhodium trichloride), and 11.8% in weight of Zr (as zirconium nitrate). After each immersion the gauze is dried at 140 ° C and calcined for 2 hours at 700 ° C. The resulting gauze comprised 3.1 wt.% Rh and 4.6 wt.% Zr based on the total weight of the gauze.

A 12 mm diameter reactor tube was filled with 1.50 g of the gauze described above comprising Rh / Zr (first layer) on top of an amount of 1.57 g of a foam comprising Ir / Zr ( second layer) that was prepared as described in example 4. .2 . Í - ASS Z Partial catalytic oxidation A partial catalytic oxidation experiment was carried out as in Example 4. The results are shown in table 1.

Table 1: Wear and conversion of naphtha * Conversion of naphtha: quantity (by weight) of carbon oxides produced by quantity (by weight) of naphtha introduced.

It can be observed in Table 1 that the addition of platinum to the first layer produces a wear of the catalyst in the first layer, while in the absence of platinum, wear occurs in the second layer. The wear in the second layer produces a decrease in the conversion of naphtha.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property.

Claims (10)

Claims

1. A catalyst or a precursor of a catalyst in the form of a fixed distribution, characterized in that the fixed distribution comprises a first layer which, during normal operation, is located at the upstream end of the distributed catalyst and comprises as the Catalytically active metal or precursor thereof, rhodium or a rhodium compound and a second layer adjacent to the first layer without space between the first and second layers, which is, during normal operation, located downstream of the first layer , the second layer comprises as the catalytically active metal or precursor thereof, iridium, osmium or platinum or a compound thereof.

2. A catalyst or a precursor of a catalyst in the form of particles of a catalyst or particles of a catalyst precursor, characterized in that it comprises a first external layer comprising as a metal 25 catalytically active or a metal precursor catalytically active rhodium or a rhodium compound and a second layer comprising as a catalytically active metal or a precursor of this catalytically active metal iridium, osmium or platinum or a compound of these metals.

3. The catalyst or a catalyst precursor according to claim 1 or 2, characterized in that the second layer comprises iridium or an iridium compound.

4. The catalyst or a catalyst precursor according to any of the preceding claims, characterized in that the amount by weight of the catalytically active metal of the second layer is at least equal to the amount of rhodium in the first layer, preferably it is at least twice the amount of rhodium in the first layer, more preferably it is at least three times that amount.

5. The catalyst or a catalyst precursor according to any of the preceding claims, characterized in that the first layer additionally comprises platinum or a platinum compound.

6. The catalyst or a catalyst precursor according to claim 5, characterized in that the proportion of rhodium to platinum (weight / weight) in the first layer is in the limit zone of 1 to 20, preferably 5 to 15. .

7. The catalyst or a catalyst precursor according to any of the preceding claims, characterized in that the catalytically active metal in at least one of the layers is associated with at least one inorganic metallic cation or a precursor of an inorganic metallic cation of Thus, the inorganic metal cation so that the inorganic metal cation is present in intimate association, supported on or with the catalytically active metal.

8. The catalyst or a catalyst precursor according to claim 7, characterized in that the inorganic metal cation S &t &? Er -? &? «&«% > »- ^ -, afc?«. «*** tii *? > j * 3 is selected from groups IIA, IIIA, IIIB, IVA, IVB and the lanthanides of the Periodic Table of Elements, and is preferably selected from Al, Mg, Zr, Ti, La, Hf, Si and Ba, and more preferably it is Zr.

9. A process for the partial catalytic oxidation of a hydrocarbon feedstock, characterized in that the process comprises contacting a feedstock comprising a hydrocarbon feedstock and an oxygen-containing gas with a catalyst according to claims 1 to 8 , preferably at a pressure in the boundary range from 1 bar to 150 bar, at a temperature in the boundary range from 750 ° C to 1400 ° C and at a space velocity per hour of the gas in the boundary range from 20,000 to 100,000. 000 Nl / kg / h.

10. The process according to claim 9, characterized in that the hydrocarbon feedstock and the oxygen-containing gas are present in amounts that produce a carbon oxygen ratio of 0.3 to 0.8, preferably 45. to 0.75.