MXPA00011853A - Vinyl acetate catalyst comprising metallic palladium, copper and gold and preparation thereof - Google Patents

Abstract

A catalyst for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid comprising a porous support on the porous surfaces of which is deposited catalytically effective amounts of metallic palladium, gold and copper, said catalyst having been prepared by steps comprising impregnating said support, the porous surfaces of which contain catalytically effective amounts of prereduced metallic palladium and copper, with a solution of potassium aurate, and reducing the potassium aurate to a catalytically effective amount of metallic gold. Alternatively, the support may first be contacted with gold followed by contact with palladium/copper complexes. A still further alternative includes use of sodium free reagents.

Description

CATALYST OF VINYL ACETATE THAT INCLUDES PALADIUM, GOLD AND METALLIC COPPER AND PREPARATION OF THE SAME BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to novel and improved catalysts for the production of vinyl acetate by reacting ethylene, oxygen and acetic acid.

RELATED TECHNIQUE It is known that vinyl acetate can be produced by reacting ethylene, oxygen and acetic acid using a catalyst consisting of metallic palladium, gold and copper deposited in a carrier. Although the process using such a catalyst is capable of producing vinyl acetate at adequate levels of productivity, any resource capable of achieving even greater productivity that involves the use of a catalyst that in some respects is easier to produce than those that are produced is obviously convenient. that have been used to date. The catalysts comprising metallic palladium, gold and copper known before this present invention are conventionally prepared by a process that includes the steps of impregnating a porous base with a single aqueous solution or different solutions of water soluble palladium, gold and copper salts; reacting the water-soluble salts impregnated with a suitable alkaline compound, for example, sodium hydroxide, to "fix" the metallic elements such as the water-insoluble compounds, for example the hydroxides; and reducing insoluble compounds in water, for example, with ethylene or hydrazine, to convert the metallic elements into the free metallic form. This type of process has the drawback of requiring several steps, sometimes including at least two fixing steps. The following references should be considered important for the invention claimed herein. The patent of E.U.A. No. 5,332,710, issued July 26, 1994 to Nicolau et al., Describes a method for preparing a catalyst useful for the production of vinyl acetate by reacting ethylene, oxygen and acetic acid, which comprises impregnating a porous base with salts of water soluble palladium and gold, fix the palladium and gold in the form of insoluble compounds in the base by immersing and stirring the impregnated base in a reactivated solution to precipitate said compounds and then reduce the compounds to the free metal form. The patent of the U.S.A. No. 5,347,046 issued September 13, 1994 to White et al., Discloses catalysts for the production of vinyol acetate by reacting ethylene, oxygen and acetic acid, comprising a palladium group metal and / or a compound thereof, gold and / or a compound thereof, and copper, nickel, cobalt, iron, manganese, lead or silver or a compound thereof, preferably deposited in a base material. British Patent No. 1, 188,777, published on April 22, 1970 describes a process for the simultaneous production of an unsaturated carboxylic acid ester, for example, vinyl acetate, by reacting an olefin, carboxylic acid and oxygen, and corresponding carboxylic acid, for example, acetic acid of its aldehyde, using a single catalyst containing a palladium compound, for example, an oxide or a salt, with one or more compounds of any of the various metals, for example metallic gold or a gold compound such as potassium aurate. The patent of E.U.A. No. 5,700,753 discloses a vinyl acetate (AV) catalyst prepared by adding organometallic gold compounds to the previously reduced palladium catalyst, prepared from Na 2 PdCl 4. The organometallic gold compound does not require a fixing process. The patent of E.U.A. No. 5,731, 457 discloses an AV catalyst prepared with non-halogen copper compound.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, a catalyst useful for the production of vinyl acetate by reacting ethylene is provided, oxygen and acetic acid with low selectivity of carbon dioxide, and said catalyst is prepared by the process that includes the steps of impregnating a porous base whose porous surfaces contain catalytically effective amounts of palladium and copper metal previously reduced, with an aurate solution of potassium (KAu02) and reduce the potassium aurate to a catalytically effective amount of metallic gold. Alternatively, the metallic gold previously reduced by the use of potassium aurate, can first be impregnated in the base, with a subsequent impregnation, fixation and reduction of Pd and Cu compounds in the base. The use of said catalyst often results in lower selectivity of carbon dioxide and heavy ends, which are generally accompanied by higher vinyl acetate productivity than when several conventional catalysts comprising metallic palladium and gold are employed. As another alternative, the catalyst can be prepared using sodium-free reagents. For example, the potassium salts of the reagents described herein can be used.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a catalyst useful for the production of vinyl acetate is provided by reacting ethylene, oxygen and acetic acid with low selectivity of carbon dioxide, and said catalyst comprises a porous base on which catalytically effective amounts are deposited. of metallic palladium, gold and copper, and is prepared through the following steps: (1) impregnate the base with catalytically effective amounts of water-soluble palladium and copper solutions with a subsequent fixation and reduction of Pd and Cu to its form metal; (2) causing the previously reduced Pd / Cu catalyst to come in contact with a solution of potassium aurate and reduce the potassium aurate to catalytically effective amounts of metallic gold. Alternatively, the base can (1) first come in contact with a solution of potassium aurate, reducing the potassium aurate to a catalytically effective amount of metallic gold; and (2) coming into contact with catalytically effective amounts of water soluble palladium and copper solutions, with a subsequent reduction of Pd and Cu to their metallic form. The use of the catalyst of the invention often results in a low selectivity of carbon dioxide, which is generally accompanied by a higher vinyl acetate productivity than when the various conventional catalysts comprising palladium metal and gold are employed. The base material of the catalyst is composed of particles having various regular and irregular shapes, such as spheres, tablets, cylinders, rings, stars and other shapes, and may have dimensions such as diameter, length or width of about 1 mm to 10 mm, preferably around 3 mm to 9 mm. We recommend spheres that have a diameter between 4 mm to 8 mm. The base material can be composed of any suitable porous substance, for example, silica, alumina, silica-alumina, titania, zirconia, silicates, aluminosilicates, titanates, spinel, silicon carbide, carbon and the like. The base material may have a density on the scale, for example, from about 0.3 g / ml to 1.2 g / ml, an absorbance on the scale, for example, from about 0.3 to 1.5 g H2O / g of base, a surface area on the scale, for example, from about 10 m2 / g to 350 m2 / g, preferably from about 100 m2 / g to 200 m2 / g, an average pore size on the scale, for example , from about 50 angstroms to 2000 angstroms, and a pore volume on the scale, for example, from about 0.1 ml / g to 2 ml / g, preferably from about 0.4 ml / g to 1.2 ml / g. In the preparation of the catalyst used in the process of the present invention, the base material is first treated to deposit catalytic amounts of palladium and copper on the porous surfaces of the base particles. Any of the various methods for achieving this purpose can be used, all of which involve impregnating the base with an aqueous solution of water-soluble compounds, for example, salts, of palladium and copper. Palladium (II) chloride, sodium-palladium (II) chloride (ie sodium tetrachloroplast (II), Na2PdCl4), potassium-palladium (II) chloride, palladium (II) nitrate or palladium sulfate ( II) are examples of suitable water-soluble palladium compounds, while, for example, cupric chloride (anhydrous or dihydrate), cupric nitrate trihydrate, cupric acetate (anhydrous or monohydrate), cupric sulfate or cupric bromide and the like can be used as copper compounds soluble in water. Sodium tetrachloropalladium (II) and cupric chloride are the recommended salts for impregnation due to their good solubility in water. Impregnation can be achieved through the "incipient moisture" method, where a quantity of water-soluble metal compound solution used for impregnation is about 95% to 100% of the absorption capacity of the material of base. The concentration of the solution is such that the amount of palladium and elemental copper in the solution absorbed in the base is equal to a predetermined amount previously desired. The impregnation is such to provide, for example, from about 1 gram to 10 grams of elemental palladium and, for example, from about 0.3 grams to 5.0 grams, preferably, from about 0.5 grams to 3.0 grams of elemental copper per liter of finished catalyst. After impregnation of the base with an aqueous solution of water-soluble palladium-copper compounds, the compounds are "fixed", ie, they are precipitated, in the form of water-insoluble compounds such as hydroxides, by reaction with an alkaline compound suitable, for example, an alkali metal hydroxide, silicate, borate, carbonate or bicarbonate, in aqueous solution. Sodium and potassium hydroxides are the preferred alkaline fixing compounds. The alkali metal in the alkaline compound should be in an amount, for example, of about 1 to 2, preferably about 1.1 to 1.8 times the amount necessary to react with the catalytically active cations present in the water soluble salt. The fixation of palladium and copper can be carried out by means of the incipient humidity method, where the impregnated base is dried, for example, at a temperature of 150 ° C for one hour, it comes into contact with a quantity of solution of alkaline material equivalent to about 95% -100% of the pore volume of the base, and allowed to rest for a period of 0.5 hours to approximately 16 hours; or the method of spin immersion, wherein the non-dried impregnated base is immersed in a solution of the alkaline material and rotated and / or rotated at least during the initial period of precipitation so that a thin band of the soluble compounds in precipitated water is formed on or near the surface of the particles of the base. The action of rotating and rotating should be performed, for example, at a speed of about 1 rpm at 10 rpm for a period, for example, of at least about 0.5 hours, preferably about 0.5 hours to 4 hours. The contemplated rotation immersion method is described in U.S. Patent No. 5,332,710, the entire disclosure of which is incorporated herein by reference. The fixed palladium and copper compounds can then be reduced, for example in the vapor phase, with ethylene, for example, 5% in nitrogen at 150 ° C for 5 hours, after first washing the catalyst containing the fixed compounds until is free of anions such as halide, and dried, for example at 150 ° C overnight under a constant purge of N2, or said reduction can be carried out in the liquid phase at room temperature with an aqueous solution of hydrazine hydrate wherein the excess of hydrazine over the amount required to reduce all metal compounds present in the base is on the scale, for example, from about 8: 1 to 15: 1, with subsequent washing and drying. Other reducing agents and means for reducing the fixed palladium and copper compounds present in the base can be employed in a conventional manner in the art. The reduction of the fixed compounds mainly causes the formation of free metals, although a smaller amount of metal oxides may also be present. Although the impregnation, fixation and reduction of palladium and copper have been described as being carried out simultaneously, in reality these three steps can be performed for palladium and copper separately. After preparing the base containing palladium and copper in the free metal form by any of the above methods, it is impregnated with an aqueous solution of potassium aurate, preferably by incipient moisture. Then, the catalyst is dried so that the catalyst contains potassium aurate in an amount sufficient to provide, for example, about 0.5 grams to 10 grams of elemental gold per liter of finished catalyst, wherein the amount of gold is around from 10% to 125% by weight based on the weight of palladium present. The potassium aurate is then reduced to metallic gold using any of the techniques described above for the reduction of palladium and copper of the fixed palladium and copper compounds on the base surface. The reduction of potassium aurate is carried out without the need for intermediate steps to fix the gold in the base in the form of a water-insoluble compound and washing said compounds until it is free of chlorine, as described above for palladium and as required normally for gold in the preparation of vinyl acetate catalysts comprising palladium and gold. The removal of the fixing and washing steps in relation to gold is an important advantage in the preparation of the catalyst of the present invention. One of the problems in producing AV catalysts has been the poor retention of noble metals in the catalyst base. The use of KAuO2 precursors often offers a method for producing highly salt-free dispersed metal particles without including the fixing step for the Au compounds. An advantage of not including the fixing step for the Au compounds is the greater gold retention since the Au is partially removed from the catalyst during the fixing / washing step contemplated in the prior art. Through this method a high metal gold retention catalyst can be obtained. The catalyst also contains Cu, Pd and Au distributed in a thin layer on the surface of the catalyst base or near said surface. Although the catalysts of the present invention have been described primarily in relation to those containing only palladium, gold and copper in the form of catalytically active metals, the catalyst may also contain one or more catalytically active metal elements in the form of free metal, oxide or combination of free metal and rust. Said metallic elements can be, for example, magnesium, calcium, barium, zirconium and / or cerium. When another metal other than palladium, gold and copper is desired in the catalyst, the base can generally be impregnated with a salt of said metal, soluble in water dissolved in the same impregnating solution containing the water soluble palladium and copper salts. In this way, the base can be impregnated at the same time with salts of palladium, copper and the additional metal soluble in water, which are then fixed and reduced in the same manner as described above for palladium and gold without any additional metal. The catalyst containing palladium and copper in the form of free metal and an additional metal in the form of oxide and / or free metal is then impregnated with potassium aurate which is subsequently reduced to gold in the form of a free metal without an intermediate fixing step as described above with respect to palladium and copper as the only additional metals other than gold. Conveniently, the catalyst containing palladium, gold and copper in free metal form, can optionally be impregnated with an alkali metal acetate solution, preferably potassium or sodium acetate, and more preferably potassium acetate (KOAc) . After drying, the finished catalyst may contain, for example, from about 10 grams to 70 grams, and preferably from about 20 grams to 60 grams of alkali metal acetate per liter of finished catalyst. Optionally, KAuO2 can be added to the previously reduced Pd / Cu catalyst together with KOAc in one step. When the vinyl acetate is prepared using the catalyst of the present invention, a gas stream, which contains ethylene, oxygen or air or acetic acid and, preferably, an alkali metal acetate, is passed over the catalyst. The composition of the gas flow can vary widely taking into account the limits for an explosion to occur. For example, the molar ratio of ethylene to oxygen may be from about 80:20 to 98: 2, the molar ratio of acetic acid to ethylene may be from about 100: 1 to 1: 100, preferably about 10. : 1 to 1: 10, and more preferably of about 1: 1 to 1: 8, and the content of gaseous alkali metal acetate may be from about 1 ppm to 100 ppm based on the weight of the acetic acid employed. The gas flow may also contain other inert gases, such as nitrogen, carbon dioxide and / or saturated hydrocarbons. The reaction temperatures that can be used are eTevated temperatures, preferably those that are on the scale of about 150 ° C-220 ° C. The pressure used can be a slightly reduced pressure, a normal pressure or a high pressure, preferably a gauge pressure of up to 20 atmospheres. The following examples illustrate the invention in greater detail.

EXAMPLES 1 TO 12 The following examples illustrate the catalyst preparation contemplated in the present invention, which contains varying amounts of palladium and gold in free metal form. A base material containing pre-reduced palladium metal was prepared as follows: The base material in an amount of 250 ml composed of silica spheres of Sud Chemie KA-160 with a nominal diameter of 7 mm, a density of about 0.562 g / ml, an absorbency of about 0.583 g of H2O / g of base, a surface area of about 160 m2 / g to 175 m2 / g and a pore volume of about 0.68 ml / g, was impregnated first by incipient humidity with 82.5 ml of an aqueous solution of sodium tetrachloropalladium (II) ( Na 2 PdCl 4) and cupric chloride (CuCl 2) in an amount sufficient to provide about 7 grams of elemental palladium and about 1.9 grams of elemental copper per liter of catalyst. The base was stirred in the solution for 5 minutes to ensure complete absorption of the solution. Then, palladium and copper were fixed to the base in the form of palladium (II) hydroxide and cupric hydroxide making the base treated by spin immersion for 2.5 hours at approximately 5 rpm to come into contact with 283 ml of a solution aqueous sodium hydroxide prepared from 50% w / w NaOH / H2O in 120% of the amount needed to convert palladium and copper to their hydroxides. The solution was drained of the treated base which was then washed with deionized water until it was free of chlorine (around 5 hours), and dried overnight at 150 ° C under constant nitrogen purge. Then, the palladium and copper were reduced to the free metal by causing the base to come in contact with ethylene (5% in nitrogen) in the vapor phase at 150 ° C for 5 hours, or with hydrazine at room temperature for 4 hours, then washing with deionized water for 2 hours and drying in an oven at 150 ° C for 5 hours, to obtain a base containing nominal quantities of 7 grams / liter of previously reduced Pd and 1.9 grams / liter of copper previously reduced. In the production of potassium aurate used to impregnate the base with gold, Auric hydroxide, Au (OH) 3l was first prepared by mixing 300 g of sodium tetrachloroor (lll), NaAuCI4 containing 0.20 g of Au / g of solution with 73.6 g 50% w / w NaOH / H2O dissolved in 200 ml of deionized water. An excess of NaOH was added to make the pH 8, and the solution was stirred and heated at 60 ° C for 3 hours to form an orange precipitate. The filtration produced an orange solid that was washed with deionized water until it was free of chlorine, and dried in a vacuum oven at 50 ° C under N2 flow, obtaining an orange-red Au (OH) 3 solid. . The analysis of the solid indicated a gold content of 79.5% by weight, which agrees with the calculated value. 0.5 grams of auric hydroxide was mixed with 0.12 grams of KOH in 35 ml of water, and the resulting orange suspension was heated to 82 ° C-85 ° C, and stirred at this temperature until all the solids dissolved to obtain a light yellow solution of potassium aurate, KAuO2 in an amount containing about 0.4 grams of elemental gold. This solution was added to 100 ml of base containing nominal amounts of 7 grams / liter of previously reduced Pd and 1.9 grams / liter of Cu reduced previously prepared as described above using ethylene as a reducing agent. The impregnation was carried out for 25-30 min. The catalyst was dried in an oven at 100 ° C for 5 hours under a flow of N 2 purge. The gold contained in the treated catalyst was then reduced with 5% ethylene in N2 at 120 ° C for 5 hours to obtain free metallic gold in the base. Finally, the catalyst was impregnated by incipient humidity with an aqueous solution of 4 g of potassium acetate in 33 ml of H 2 O, and dried in a fluidized bed drier at 100 ° C for 1 hour. The aforementioned description of the preparation of a catalyst according to the present invention is specific for the catalysts of examples 1 -3 which contain nominal amounts, ie corresponding to the concentrations and amounts of the impregnating solutions, of 7 grams of Pd, 1.9 grams of Cu and 4 grams of Au per liter of catalyst, and wherein the Pd, Cu and Au are reduced with ethylene. In Example 4, the procedures of Examples 1-3 were followed, except that the amounts of materials and reagents were increased proportionally so as to obtain a batch of 6 liters of catalyst containing the same nominal amounts of copper, palladium and gold than the catalyst in examples 1-3. The catalysts of Examples 5-12 which may contain amounts of Pd, Cu and / or Au other than the amounts of Examples 1 - 3 are prepared in a similar manner, except that the concentration of Na2PdCl4, CuCl2 and / or KAu02 in the suitable impregnating solution varies to obtain the desired nominal amounts of Pd, Au and / or Cu in the base, and the reduction of Pd, Cu and Au is carried out with either ethylene or hydrazine, as described above. The reducing agent (Red.) Used in the preparation (C4H4 or N2H4), the nominal amounts of Pd, Cu and Au corresponding to the concentrations and amounts of impregnating solutions (Cant. Nom., G / l), and actual amounts of Pd, Cu and Au in the catalysts of Examples 1-12 determined by analysis, in terms of percentage of total catalyst including base (% Cat. Tot.) And percentages of nominal amounts (% of Cant. Nom.) Are shown in Table I. The catalysts of the examples were tested for their activity and selectivity to various by-products in the production of vinyl acetate by reacting ethylene, oxygen and acetic acid. For this purpose, about 60 ml of catalyst prepared in the manner described were placed in a stainless steel basket with a temperature capable of being measured with a thermocouple in both the upper and lower part of the basket. The basket was then placed in a continuously agitated Berty reservoir reactor of the recirculating type, and maintained at a temperature that provided about 45% oxygen conversion with an electric heating plate. A gaseous mixture of about 50 normal liters (measured at normal temperature and pressure) of ethylene, about 10 normal liters of oxygen, about 49 normal liters of nitrogen, about 50 g of acetic acid, and about 4 mg of Potassium acetate was circulated at a pressure of about 12 atmospheres through the basket, and the catalyst was allowed to rest under these reaction conditions for at least 16 hours before a second two-hour process, after which the reaction ended. The analysis of the products carried out by means of online gas chromatography analysis combined with the analysis of off-line liquid products condensing the flow of the product at around 10 ° C to achieve an optimal analysis of carbon dioxide (CO2), Heavy ends (HE) and ethyl acetate (EtOAc) of the final products, whose result was used to calculate the selectivities of these materials for each example (ex.) as shown in table I. The relative activity of the reaction expressed as an activity factor (Act.) are also shown in table I, and calculated by means of a computer as follows: The computer program uses a series of equations that relate the activity factor to the temperature of the catalyst (during the reaction), conversion of oxygen and a series of kinetic parameters for the reactions that occur during the synthesis of AV. More generally, the activity factor is inversely related to the temperature necessary to achieve a constant oxygen conversion.

TABLE 1 00 The values shown in Table 1 indicate that the catalysts of the present invention can in many cases be used to synthesize vinyl acetate by reacting ethylene, oxygen and acetic acid with selectivities lower than CO2 and heavy ends than the various conventional catalysts and / or commercials that include palladium and gold, while maintaining satisfactory levels of activity. Here is my revised opinion regarding this: EXAMPLE 13 Preparation of AV catalyst by the impregnation of (1) KAuO2 and then (2) Pd or Pd / Cu. The base material in an amount of 100 ml composed of Sud Chemie KA-160 silica spheres with a nominal diameter of 7 mm, a density of about 0.562 g / ml, an absorbency of about 0.583 g H2O / g of base, a surface area of about 160m2 / g to 175 m2 / g and a pore volume of about 0.68 ml / g was first impregnated by incipient humidity with 35 ml of aqueous solution of KAuO2 (prepared as in examples 1-12) in enough quantity to provide about 4 grams of elemental gold per liter of catalyst. The base was stirred in the solution for 5 minutes to ensure complete absorption of the solution. The treated base was placed in an oven, and dried for 5 hours at 100 ° C under constant purge of N2. The reduction was carried out with 5% C2H4 in N2 at 120 ° C for 5 hours.

Then, this previously reduced gold catalyst was impregnated by incipient humidity with 35 ml of aqueous solution of sodium tetrachloropalladium (II) (Na2PdCI4) and cupric chloride (CuCl2) in sufficient quantity to provide about 7 grams of elemental palladium and about 1.9 grams of elemental copper per liter of catalyst. The base was stirred in the solution for 5 minutes to ensure complete absorption of the solution. Then, palladium and copper were fixed to the base as palladium (II) hydroxide and cupric hydroxide causing the base treated by spin immersion for 2.5 hours at approximately 5 rpm to come in contact with 120 ml of sodium hydroxide solution aqueous prepared from 50% w / w NaOH / H2O in an amount of 120% of the amount needed to convert palladium and copper to their hydroxides. The solution was drained of the treated base, which was then washed with deionized water until free of chlorine (about 5 hours), and dried overnight at 150 ° C under constant nitrogen purge. Subsequently, the palladium and copper were reduced to the free metal by causing the base to come in contact with ethylene (5% in nitrogen) in the vapor phase at 150 ° C for 5 hours, or with hydrazine at room temperature for 4 hours, washing then with deionized water for 2 hours and drying in an oven at 150 ° C for 5 hours to obtain a catalyst containing nominal amounts of 4 g / liter of Au, 7 grams / liter of Pd and 1.9 grams / liter of Cu. This catalyst was then impregnated with 4 g of KOAc in 33 ml of H2O and dried in a fluidized bed drier at 100 ° C for 1.5 hours.

Catalyst yield of Pd / Au / Cu: CO2 8.80 Activity 1.87 HE 0.702 EtOAc 0.078

Claims (39)

NOVELTY OF THE INVENTION CLAIMS

1. - A catalyst for the production of vinyl acetate by reacting ethylene, oxygen and acetic acid, characterized in that it comprises a porous base on the porous surfaces where catalytically effective amounts of metallic palladium, gold and copper are deposited, and which is prepared by the process comprising the steps of impregnating said porous base, the porous surfaces of which contain catalytically effective amounts of palladium and copper metal previously reduced, with a solution of potassium aurate and reducing the potassium aurate to a catalytically effective amount of metallic gold.

2. The catalyst according to claim 1, further characterized in that the base containing palladium and copper previously reduced is prepared by the process comprising the steps of impregnating said base with an aqueous solution of palladium and copper salts soluble in water , fixing said palladium and copper in the form of water-insoluble compounds through the reaction with a suitable alkaline compound, and reducing to its free metallic state the insoluble compounds in palladium and copper water present in the base.

3. The catalyst according to claim 2, further characterized in that the water-soluble palladium salt is sodium tetrachloropalladium (II), and said water-soluble copper salt is cupric chloride.

4. The catalyst according to claim 1, further characterized in that it contains from about 1 gram to 10 grams of palladium, from about 0.5 grams to 10 grams of gold, and from about 0.3 grams to 5.0 grams of copper per liter of the catalyst and wherein the amount of gold is around 10% to 125% by weight based on the weight of palladium.

5. The catalyst according to claim 1, further characterized in that it also contains a deposit of an alkali metal acetate.

6. The catalyst according to claim 5, further characterized in that said alkali metal acetate is potassium acetate which is present in an amount of about 10 grams / liter to 70 grams / liter of catalyst.

7. A catalyst for the production of vinyl acetate by reacting ethylene, oxygen and acetic acid, characterized in that it comprises a porous base on the porous surfaces where catalytically effective amounts of metallic palladium, gold and copper are deposited, and which is prepared by the process comprising the steps of impregnating said porous base, with a potassium aurate solution, reducing the aurate to a catalytically effective amount of metallic gold, contacting the gold-based catalyst with soluble palladium and copper compounds in water, and fix and reduce the palladium and copper compounds to their metallic state.

8. - The catalyst according to claim 7, further characterized in that the catalyst is prepared with sodium-free reagents.

9. The catalyst according to claim 7, further characterized in that the catalyst forms a thin layer of Pd, Au and Cu on the surface of the base.

10. The catalyst according to claim 7, further characterized in that it also contains a deposit of an alkali metal acetate. 1.

The catalyst according to claim 1, further characterized in that the catalyst is prepared with sodium-free reagents.

12. The catalyst according to claim 1, further characterized in that potassium aurate is simultaneously added with potassium acetate.

13. A method for preparing a catalyst for the production of vinyl acetate by reacting ethylene, oxygen and acetic acid, further characterized in that it comprises impregnating a porous base whose porous surfaces contain catalytically effective amounts of palladium and copper previously reduced, with a solution of potassium aurate, and reduce the potassium aurate to a catalytically affective amount of metallic gold.

14. The method according to claim 13, further characterized in that the base containing palladium and copper reduced previously is prepared by the process comprising the steps of impregnating said base with an aqueous solution of palladium and copper salts soluble in water, fixing said palladium and copper in the form of insoluble compounds in water by reaction with a suitable alkaline compound, and reducing to its free metal state the water-insoluble palladium and copper compounds present in the base.

15. The method according to claim 14, further characterized in that the water-soluble palladium salt is sodium tetrachloropalladium (II) and the water-soluble copper salt is cupric chloride.

16. The method according to claim 13, further characterized in that said porous base contains from about 1 gram to 10 grams of palladium, from about 0.5 grams to 10 grams of gold, and from about 0.3 grams to 5.0 grams of copper per liter of catalyst, and the amount of gold from about 10% to 125% by weight based on the weight of palladium.

17. The method according to claim 13, further characterized in that said catalyst is impregnated with a solution of an alkali metal acetate.

18. The method according to claim 17, further characterized in that the alkali metal acetate is potassium acetate which is deposited in the catalyst in an amount of about 10 grams / liter to 70 grams / liter of catalyst.

19. - The method according to claim 17, further characterized in that potassium aurate is simultaneously added with potassium acetate.

20. The method according to claim 13, further characterized in that the catalyst is prepared with sodium-free reagents.

21. A method for preparing a catalyst for the production of vinyl acetate by reacting ethylene, oxygen and acetic acid, characterized in that it comprises impregnating a porous base with a solution of potassium aurate, reducing the aurate to a catalytically effective amount of gold metallic, contact the gold-based catalyst with water-soluble palladium and copper compounds, and fix and reduce the palladium and copper compounds to their metallic state.

22. The method according to claim 21, further characterized in that the catalyst is prepared with sodium-free reagents.

23. The method according to claim 21, further characterized in that the catalyst forms a thin layer of Pd, Au and Cu on the surface of the base.

24. The method according to claim 21, further characterized in that it also contains a deposit of an alkali metal acetate.

25. - The method according to claim 24, further characterized in that potassium aurate is added simultaneously with potassium acetate.

26. The method according to claim 13, further characterized in that the catalyst forms a thin layer of Pd, Au and Cu on the surface of the base.

27. A process for the production of vinyl acetate by reacting ethylene, oxygen and acetic acid in the form of reagents, characterized in that it comprises causing said reagents to come into contact with a catalyst comprising a porous base on whose porous surfaces amounts are deposited. catalytically effective metallic palladium, gold and copper, and wherein said catalyst has been prepared by the process comprising the steps of impregnating said porous base, whose porous surfaces contain catalytically effective amounts of palladium and copper metal previously reduced with an aurate solution of potassium, and reduce the potassium aurate to a catalytically effective amount of metallic gold.

28. The process according to claim 27, further characterized in that the base containing palladium and copper previously reduced is prepared by a process comprising the steps of impregnating said base with an aqueous solution of palladium and copper salts soluble in water , fixing said palladium and copper in the form of water-insoluble compounds through the reaction with a suitable alkaline compound, and reducing to its free metallic state the water-insoluble palladium and copper compounds present in the base.

29. The process according to claim 28, further characterized in that the water-soluble palladium salt is sodium tetrachloropalladium (II) and the water-soluble copper sai is cupric chloride.

30. The process according to claim 27, characterized in that the catalyst contains from about 1 gram to 10 grams of palladium, from about 0.5 grams to 10 grams of gold and from about 0.3 grams to 5.0 grams of copper per liter of catalyst, and wherein the amount of gold is around 10% to 125% by weight based on the weight of palladium.

31. The process according to claim 30, further characterized in that the catalyst also contains a deposit of an alkali metal acetate.

32. The process according to claim 31, further characterized in that said alkali metal acetate is potassium acetate which is deposited in the catalyst in an amount of about 10 grams / liter to 70 grams / liter of catalyst.

33. The process according to claim 31, further characterized in that potassium aurate is simultaneously added with potassium acetate.

34. - The process according to claim 27, further characterized in that the catalyst is prepared with sodium-free reagents.

35.- A process for the production of vinyl acetate by the reaction of ethylene, oxygen and acetic acid as reagents through the steps comprising contacting said reagents with a catalyst comprising a porous base on whose porous surfaces catalytic amounts are deposited effective metallic palladium, gold and copper, said catalyst has been prepared by the steps comprising impregnating said porous base with a solution of potassium aurate, reducing the aurate to a catalytically effective amount of metallic gold, contacting the catalyst with base of gold with water-soluble palladium and copper compounds, and fix and reduce the palladium and copper compounds to their metallic state.

36. The process according to claim 35, further characterized in that the catalyst is prepared with sodium-free reagents.

37.- The process according to claim 35, further characterized in that the catalyst forms a thin layer of Pd, Au and Cu on the surface of the base.

38. The process according to claim 35, further characterized in that it also contains a deposit of an alkali metal acetate.

39. - The process according to claim 38, further characterized in that potassium aurate is simultaneously added with potassium acetate. 40.- The process according to claim 27, further characterized in that the catalyst forms a thin layer of Pd, Au and Cu on the surface of the base.