WO2016198561A1

WO2016198561A1 - Electroless deposition of au-pd bimetallic catalysts for alkenyl acetate production

Info

Publication number: WO2016198561A1
Application number: PCT/EP2016/063236
Authority: WO
Inventors: Jayakiran REBELLI; Alex J. SEI; Jason Carson; Brett SMOTHERS; Chris J. BAUER; Cristiano Trionfetti; Falk HEINROTH; Ralf Hausmann
Original assignee: Evonik Degussa Gmbh
Priority date: 2015-06-12
Filing date: 2016-06-10
Publication date: 2016-12-15
Also published as: TW201716139A

Abstract

The present invention relates to a process for the preparation of a Au-Pd bimetallic shell-type catalyst, comprising the following steps: a. providing a solid, shaped body catalyst support, b. contacting the support with two solutions, one solution containing Au ions in an amount of from 0.1-10 wt% and the other solution containing Pd ions in an amount of from 0.1-10 wt%, with the proviso that the weight ratio of Pd:Au is in the range of from 0.2:1 to 4:1. c. reducing the plated support with hydrogen to obtain the Au-Pd bimetallic shell-type pre-catalyst, d. contacting the Au-Pd bimetallic pre-catalyst with an aqueous potassium acetate solution with a content of potassium in the range of from 0.1-10 wt%, e. drying to obtain the Au-Pd bimetallic shell-type catalyst. The invention further relates to a process for the production of alkenyl acetates, applying the Au-Pd bimetallic catalyst.

Description

Electroless deposition of Au-Pd bimetallic catalysts for alkenyl acetate production

The present invention relates to a method for the production of Au-Pd bimetallic catalysts as well as the use of as-prepared catalysts for alkenyl acetate production, especially for the production of vinyl acetate.

Vinyl acetate is an important industrial material used in a wide range of fields including coatings, adhesives, fiber treatment agents and the like, as a starting material for vinyl acetate resins, as a starting material for polyvinyl alcohols, and as a monomer for copolymerisation with ethylene, styrene, acrylate, methacrylate and other monomers.

Catalysts consisting of noble metals such as Pd and Au are commonly used for production of alkenyl acetates obtained using acetic acid, lower olefins and oxygen as starting materials, and especially vinyl acetate.

An extremely important technical problem in the production of vinyl acetate is achieving increased vinyl acetate selectivity, while inhibition of carbon dioxide gas generation is also important from the viewpoint of the environmental load. Lengthening the lifetime of the catalyst/keeping the metals leaching to a minimum are further important issues for industrial production of vinyl acetate from an economical standpoint.

Catalysts for production of vinyl acetate which are of the„shell" type, having palladium or gold supported only on the surface of the carrier are considered to have superior reactivity. Methods for preparation of shell-type catalysts are disclosed.

Catalysts for the production of vinyl acetate monomer (VAM) are typically prepared by

impregnation techniques or layered deposition of active metals.

US5808136 discloses a process for the preparation of a supported catalyst using impregnation techniques. The process comprises the steps of (a) impregnating support particles (KA-160 of Sudchemie or AEROSIL® 350 of Degussa) with a solution containing potassium hydroxide, (b) drying the support, (c) impregnating the support with a solution containing tetrachloroauric acid and potassium palladium chloride for 20 h, (d) reducing in the aqueous phase with hydrazine for 4 h, (e) washing and drying, (f) impregnating the support with a solution containing potassium acetate, (g) and drying. This catalyst is useful in the production of vinyl acetate monomer.

WO99/08790 discloses a process for the preparation of a supported shell-type catalyst using impregnation techniques. The process comprises the steps of (a) impregnating or spraying an S1O2 support (Siliperl® of Engelhard or AEROSIL® 200 of Degussa) with a solution containing palladium chloride and tetrachloroauric acid, (b) drying the support, (c) reducing in the aqueous phase with a solution containing tripotassium citrate or trisodium citrate, and (d) drying.

WO2010/060649 discloses a process for the preparation of a supported shell-type catalyst using impregnation techniques. The process comprises the steps of (a) generating a fluidized bed of catalyst support shaped bodies, which are made of activated and Zr-doped Bentonit, by means of 90 °C hot air, wherein the catalyst support shaped bodies perform a toroidal movement, (b) spraying the outer shell of the circulating catalyst support shaped bodies with a first solution containing Pd(NH3)(OH)2 for 0.5 h, (c) calcining in air for 2 h at a temperature of 350 °C, (d) generating a fluidized bed of the catalyst support shaped bodies by means of 90 °C hot air, wherein the catalyst support shaped bodies perform a toroidal movement, (e) spraying the outer shell of the circulating catalyst support shaped bodies with a second solution containing KAuCh for 0.5 h, (e) reducing for 5 h at a temperature of 200 °C in a mixture of 5 vol-% H2 in N2, (f) impregnating the catalyst support shaped bodies by incipient wetness with a solution containing potassium acetate, and (g) drying. This catalyst is useful in the production of vinyl acetate monomer.

WO2012/004334 discloses a process for the preparation of a supported shell-type catalyst using impregnation techniques. The process comprises the steps of (a) providing catalyst support shaped bodies, comprising charging an aircoater device with the catalyst support shaped bodies and causing a circulation of the catalyst support shaped bodies by means of 70 °C hot air, (b) spraying the outer shell of the circulating catalyst support shaped bodies with a solution containing

Pd(NH3)(OH)2 and KAuCh, (c) reducing in forming gas at a temperature of from 50 °C to 150 °C, and (d) impregnating the catalyst support shaped bodies by incipient wetness with a solution containing potassium acetate, (e) drying. This catalyst is useful in the production of vinyl acetate monomer.

WO2008/145386 discloses a process for the preparation of supported shell-type catalysts using impregnation techniques. The process comprises the steps of (a) providing a porous, solid, shaped body support (KA-160 of Sudchemie), (b) impregnating the support by incipient wetness with a first metal solution containing Pd(NH3)(OH)2, (c) impregnating the support with a solution containing formic acid, (d) drying, (e) impregnating the support by incipient wetness with a second metal solution containing KAuCh, (f) impregnating the support with a solution containing formic acid, (g) reducing in an aqueous solution containing NahbPC , and (h) drying. This catalyst is useful in the production of vinyl acetate monomer.

W099/62632 discloses a process for the preparation of a supported shell-type catalyst using impregnation techniques. The process comprises the steps of (a) impregnating porous silica spheres (KA-160 of Sudchemie) by incipient wetness with a solution containing Na2PdCU, (b) fixing palladium as palladium hydroxide by contacting the support with NaOH, (c) washing and drying the support, (d) reducing palladium to the free metal by contacting the support with ethylene or with hydrazine, (e) contacting the prereduced palladium catalyst with a solution containing KAuCh, (f) drying and reducing gold to the free metal by contacting the catalyst with ethylene or with hydrazine, (g) impregnating the catalyst by incipient wetness with a solution containing potassium acetate, and (h) drying.

WO2008/029597 discloses a process for the preparation of a supported shell-type catalyst using impregnation techniques. The process comprises the steps of (a) impregnating a silica spherical support (HSV-I by Shanghai Kaigen) by incipient wetness with an aqueous solution containing Na2SiO3*9H20, (b) immersing the support in an aqueous solution containing Na2PdCU and HAuCU, (c) adding a solution containing hydrazine hydrate, (d) washing and drying, and (e) impregnating by incipient wetness with a solution containing potassium acetate and drying. Impregnation techniques are simple and versatile preparation methods. Metal distribution throughout the support material can be achieved as well as shell-type distribution onto the support material. However, such methods often do not effectively control the distribution or homogeneity of metals on the support. Furthermore, it is difficult to control shell-thickness and penetration depth of the impregnating solution. Typically, special equipment is applied to immediately dry the support after impregnation for this purpose. Such methods are deemed to be inefficient and inexpedient for industrial scale production since the proportion of deficient products is unacceptable.

Further techniques are known to deposit metals onto supports in a controlled manner to obtain supported catalysts. The most important techniques are electrodeposition and electroless deposition.

US6207128 discloses a process for the preparation of supported metal catalysts using electroless deposition techniques. The process comprises the steps of (a) immersing a porous monolithic silica support in an acidic aqueous solution of SnCl2*2H20 as sensitizer for 2 minutes; (b) washing with water; (c) immersing the support in an aqueous solution containing PdCk, Nh and NhUCI for 2 minutes; (d) immersing the support in an aqueous solution containing NaH2P02*2H20 for 45 minutes; (e) washing in an acidic aqueous solution for 10 minutes and drying at 50°C over night. This catalyst is useful in a process of producing hydrogen peroxide according to the anthraquinone process.

Monnier et al. (Journal of Catalysis 2010, 270, 224-233) discloses a process for the preparation of Au-Pd bimetallic catalysts using electroless deposition techniques. The process comprises the steps of suspending a commercially available powdered 1.85 wt% Pd/SiCh catalyst (8.6 % Pd dispersion) in an electroless bath containing HAu(CN)2 and N2H4 as reducing agent to deposit the metal onto the Pd/SiCh catalyst. The S1O2 support is a powdered S1O2 with a surface area of 100 m²/g, a pore volume of 0.75 cm³/g and a particle size in the range of 150-300 μιτι. The bimetallic catalysts are useful in the hydrogenation of propylene.

Monnier et al. (Catalysis Today 201 1 , 160, 170-178) discloses a process for the preparation of silica supported, group IB-Pd bimetallic catalysts using electroless deposition techniques. The process comprises the steps of suspending a commercially available powdered 1.85 wt% Pd/SiC catalyst (8.6 % Pd dispersion) in an electroless bath containing Ag, Au or Cu ions and a reducing agent to deposit the metal onto the Pd/SiC catalyst. The S1O2 support is a powdered S1O2 with a surface area of 86 m²/g, a pore volume of 0.75 cm³/g and a particle size in the range of 150- 300 μιτι. These bimetallic catalysts are useful in hydrogenation reactions, for example the selective oxidation and hydrogenolysis of glycerol.

Jayakiran Rebelli discloses in his PhD Thesis (Preparation, Characterization, and Evaluation of Bimetallic Catalysts Prepared by Electroless Deposition Methods, University of South Carolina 201 1 , UMI Dissertation Publishing, number 3454801 ) a process for the preparation of M-Pd/SiC bimetallic catalysts, wherein M = Au, Ag or Cu. The process comprises the steps of suspending a commercially available powdered 1.85 wt% Pd/SiC catalyst (8.6 % Pd dispersion)in an electroless bath containing bis-cyano salts of Ag, Au or Cu and a reducing agent to deposit the metal onto the catalyst. The S1O2 support is a powdered S1O2 with a surface area of 86 m²/g, a pore volume of 0.75 cm³/g and a particle size in the range of 150-300 μιτι. This catalyst is useful in the hydrogenation of glycerol.

Therefore, the technical problem of the present invention is to provide a method for the preparation of Au-Pd bimetallic catalysts that is economically advantageous while the as-prepared catalysts meet several requirements:

- the performance of the catalyst with regard to activity and selectivity in the production of VAM is not negatively affected,

metal leaching is kept to a minimum during production of catalyst,

- catalysts are stable and resistant to leaching while in contact with water and other hot liquids during the production of VAM.

INVENTION

The present invention includes several equivalent embodiments to solve the technical problem. These embodiments differ in the sequential order and method of metal deposition. The sequential order of the deposition of metals is not important. Pd may be deposited before Au or Au may be deposited before Pd or Au and Pd may be deposited simultaneously. Although preferred, it is not essential that both metals are deposited through electroless deposition. The electroless solutions comprising of either Au or Pd and both Au and Pd in the present invention are called as solutions hereafter unless specified. One of the metals may be deposited by other known impregnation methods as well. It is also possible to employ a commercially available precious metal catalyst containing Au or Pd on a solid, shaped body support and to plate the other metal by electroless deposition. However, the as-prepared catalysts show good performance in VAM production.

The invention provides a process for the preparation of a Au-Pd bimetallic shell-type catalyst, comprising the following steps

a. providing a solid, shaped body catalyst support,

b. contacting the support with two solutions, one solution containing Au ions in an amount of from 0.1-10 wt%, preferably 0.1-2 wt%, more preferable 0.2-0.75 wt%, and the other solution containing Pd ions in an amount of from 0.1-10 wt%, , preferably 0.1-2 wt%, more preferable 0.5-1.5 wt%,

with the proviso that the weight ratio of Pd:Au is in the range of from 0.2:1 to 4:1.

c. reducing the plated support with hydrogen to obtain the Au-Pd bimetallic shell-type pre- catalyst,

d. contacting the Au-Pd bimetallic pre-catalyst with an aqueous potassium acetate solution with a content of potassium in the range of from 0.1-10 wt%,

e. drying to obtain the Au-Pd bimetallic shell-type catalyst.

In a special embodiment of this process the support is first contacted with a solution containing ions of a first metal, wherein the first metal is selected from gold and palladium to obtain a plated support comprising gold or palladium,

this support is aged, washed and dried before contacting it with a solution containing ions of a second metal, wherein the second metal is palladium when the first metal is gold and that is gold when the first metal is palladium, to obtain a plated support comprising gold and palladium, this support is aged and dried, before being reduced with hydrogen.

In a first preferred embodiment of this process, the first metal is Pd and the second metal is Au, wherein the solution containing palladium is an aqueous solution of Na2PdCU and N2H4, and the molar ratio of Na2PdCU : N2H4 is 1 :1 - 1 :30, more preferably 1 :1 - 1 :10.

In a second preferred embodiment of this process, the first metal is Pd and the second metal is Au, wherein the solution containing gold is an aqueous solution comprising of KAu(CN)2 and N2H4, and the molar ratio of KAu(CN)₂ : N2H4 is 1 :1 - 1 :3, more preferably 1 :1 - 1 :10.

For the first and second embodiment it is possible to reduce the plated support comprising palladium in liquid phase or gas phase before the deposition of Au.

In a third preferred embodiment of this process, the first metal is Au and the second metal is Pd, wherein the solution containing palladium is an aqueous solution of Na2PdCU and N2H4, and the molar ratio of Na2PdCU : N2H4 is 1 :1 - 1 :30, more preferably 1 :1 - 1 :10.

In a fourth preferred embodiment of this process, wherein the first metal is Au and the second metal is Pd, wherein the solution is an aqueous solution of KAu(CN)2 and N2H4, the molar ratio of KAu(CN)₂ : N2H4 is 1 :1 - 1 :30, more preferably 1 :1 - 1 :10.

For the third and fourth embodiment it is possible to reduce the plated support comprising the plated support is further reduced in liquid phase or gas phase before the deposition of Pd.

The invention further provides a process for the preparation of a Au-Pd bimetallic shell-type catalyst, comprising the following steps:

a. providing a precious metal catalyst containing 0.1-10 wt-% of a first metal selected from

palladium and gold on a solid, shaped body support,

b. contacting the precious metal catalyst with an solution containing ions of a second metal in an amount in the range of from 0.1-10 wt-%, wherein the second metal is palladium when the first metal is gold and that is gold when the first metal is palladium, with the proviso that the weight ratio of Pd:Au is in the range of from 0.2:1 to 4:1 ,

d. contacting the Au-Pd bimetallic pre-catalyst with an aqueous potassium acetate solution with a content of potassium in the range of from 0.1-10 wt-%,

e. drying to obtain the Au-Pd bimetallic shell-type catalyst.

a. providing a solid, shaped body catalyst support,

b. contacting the support with a solution containing ions of Au and Pd, wherein the amount of Au in the solution is in the range of from 0.1-10 wt%, preferably 0.1-2 wt%, more preferable 0.2-

0.75 wt%, and of

Pd in the solution 0.1-10 wt%, preferably 0.1-2 wt%, more preferable 0.5-1.5 wt%, with the proviso that the weight ratio of Pd:Au is in the range of from 0.2:1 to 4:1 , c. reducing the plated support with hydrogen to obtain the Au-Pd bimetallic shell-type pre- catalyst,

e. drying to obtain the Au-Pd bimetallic shell-type catalyst.

The pH of the solution containing Pd ions and/or the solution containing Au ions is preferably 8 -12, more preferably 9 - 10. Adjusting the pH can be achieved by addition of alkali solution such as NaOH or KOH.

In another preferred embodiment the solution containing Pd ions and/or the solution containing Au ions further comprises hydrazine, formaldehyde, dimethylamine borane (DMAB) and/or sodium borohydride, hydrazine being the most preferred one.

The support of the present invention is a solid, shaped body support. The form of the solid, shaped body may be in the form of spheres, extrudates, cut extrudates, trilobes, stars, rings, cylinders, or pellets.

The support material may be selected from the group consisting of metal oxides, minerals and silicates. Preferably, the catalyst support material is selected from the group consisting of silica, alumosilicate, titania, alumina, zirconia, yttria, and mixtures thereof. More preferably, the support material is silica or alumosilicate, such as spherical S1O2 KA-160, Clariant.

Preferred are aqueous solutions of metal sources such as cyanides, chlorides, nitrates, sulphates, etc., of gold and palladium and preferred reducing agents are hydrazine, formaldehyde, dimethylamine borane (DMAB), sodium borohydride, and hydrogen.

The most preferred Au source is KAu(CN)2, the most preferred Pd source is Na2PdCU and the most preferred reducing agent is N2H4.

Optionally additives, such as complexing agents, stabilizers, depolarizers, and/or promoters can be present in the electroless plating solution. However, a single compound can act as one or more of these additives. Typical examples of complexing agents are organics, phosphates, cyanides or amine compounds, such as cyanide, sulfate, citrate, chloride, and ethanolamine for gold and such as ethylendiamine, citrate, succinate, acetate, and ammonium for palladium. Typical examples of stabilizers are Na2EDTA and citric acid. Depolarizer may be applied in borohydride and DMAB plating solutions to increase the deposition rate, typical examples of depolarizers are ions like Pb²⁺ and Tl²⁺. Promoters are applied to increase the anodic partial oxidation, typical examples of promoters are carbonate or triethylamine in DMAB solutions and lead acetate or K2CO3 in hydrazine solutions.

With regard to the final catalyst, the calculated amount of Pd is in the range of from 0.1 to 10.0 wt% and the calculated amount of Au is in the range of from 0.1 to 10.0 wt% with the proviso that the

Pd:Au weight ratio is in the range of from 0.2:1 to 4:1. Preferred is a calculated amount of Pd in the range of from 0.1-2.0 wt% and a calculated amount of Au in the range of from 0.1-2.0 wt%. Even more preferred is a calculated amount of Pd in the range of from 0.5-1.5 wt% and a calculated amount of Au in the range of from 0.2-0.75 wt%. Contacting in the sense of the present invention describes any process to bring the solution into contact with the support, such as spraying, immersing, dipping, sprinkling, wetting and the like. The temperature of the plating process, i.e. solution and/or support, is maintained in a range of from 15 °C - 85 °C, preferably in the range of from 20 °C - 25 °C.

Contacting may further include well-known steps of aging, washing and drying the plated support.

Aging in the sense of the present invention is defined as a process where no action, especially no mixing, is performed. Preferably, aging is performed for a period of 2-8 h at ambient temperature. Ambient temperature in the sense of the present invention is defined as a temperature in the range of from 20 °C to 25 °C.

Drying is performed at elevated temperature in air until a desired water content is reached.

Preferably, drying is performed at a temperature in the range of from 80 °C to 110 °C, more preferably at a temperature in the range of from 100 °C to 110 °C. It is advantageous that the moisture content after drying is below 5 wt%.

Washing may be performed with de-ionised water to remove any undesired residues, such as chloride, nitrate, etc.

Reducing with hydrogen in the sense of the present invention is defined as reducing with pure hydrogen or any suitable mixture of H2 with inert gas like forming gas at a temperature in a range of from 200-700 °C, preferably in a range of from 300-600 °C, more preferably at 450-600 °C.

Preferably, a forming gas mixture of 5 % H2/95 % N2 is applied at a temperature in a range of from 200-700 °C, preferably in a range of from 300-600 °C, more preferably at 450-600 °C.

Reducing in liquid phase in the sense of the present invention is defined as a reducing step, wherein reduction in liquid phase is performed with an aqueous solution of a reducing agent selected from N2H4, HCHO, Na₂H₂P02, NaBH₄, NaBhU+NaOH, and HCOONa, at a temperature in the range of from 15-45 °C,

The average particle size of precious metal particles on the surface of the final catalyst as obtained by the present processes usually is in the range of from 2-8 nm, wherein most of the particles may exhibit a particle size in the range of from 3-6 nm. The average particle size is measured by SEM and TEM spectroscopy.

The surface of the catalyst is defined as up to 5 nm depth in radial direction from the exterior of the final catalyst. The metal composition is measured by TEM-EDS (transmission electron microscopy coupled with energy dispersive X-ray spectroscopy).

The total shell thickness of the final catalyst as obtained by the present processes usually is in a range of from 5-300 μιτι, preferably in the range of from 5-200 μιτι. The shell thickness is measured by SEM spectroscopy.

The calculated amount of potassium on the final catalyst is in the range of from 0.1 to 10 wt%, preferably in the range of from 2 to 4 wt%. A further embodiment of the present invention relates to a process for the production of alkenyl acetates wherein a Au-Pd bimetallic shell-type catalyst prepared according to the present invention is applied. In a preferred embodiment the alkenyl acetate is vinyl acetate.

Alkenyl acetate production

The reaction for alkenyl acetate production according to the invention is preferably carried out in a gas phase using acetic acid, a lower olefin and oxygen as the reaction starting materials.

For example, the reaction scheme may be the following when the lower olefin is ethylene:

C₂H₄ + CH₃COOH + ¹/_{2 2} → CH₂ = CHOCOCH₃ + H₂0 The proportion of the acetic acid, lower olefin and oxygen starting materials, in terms of volume ratio, is preferably acetic acid : lower olefin : oxygen = 1-1 1 : 1-15 : 0.5-2.

When the lower olefin is ethylene the volume ratio is preferably acetic acid : ethylene : oxygen = 3: 15: 1. When the lower olefin is propylene the volume ratio is preferably acetic acetic acid :

propylene : oxygen = 1 : 1-12 : 0.5-2.

There are no restrictions to the lower olefin. Typically lower olefins are C2-Cs-olefins, like ethylene, propylene, 1-butene, 2-butene, butadiene and other C4-derivatives, isoprene, piperylene.

Preferably the lower is olefin is ethylene or propylene.

It is generally preferred to use a high purity material, but admixture with a lower saturated hydrocarbon such as methane, ethane or propane is also satisfactory.

The starting gas for the reaction contains acetic acid, lower olefin and oxygen, and if necessary nitrogen, carbon dioxide or a rare gas may be included as a diluent. Proportion in terms of molar ratio of reaction starting materials and diluent is preferably reaction starting

materials : diluent = 1 : 0.05-9, more preferably 1 : 0.1-3.

The oxygen is also not restricted in any particular way. The oxygen may be diluted with an inert gas such as nitrogen or carbon dioxide gas, and it may be supplied in air, for example, but when the reactive gas is circulated it is advantageous to use oxygen of high concentration, and preferably 99% or greater.

The reaction is conducted as a fixed bed flow reaction, the starting gas is preferably flowed through the reactor at a space velocity (GHSV = 10 h - 15,000 hr ; preferably 3000 h - 8000 hr ) under standard reaction conditions of T and P as described below. There is no particular restriction to the reaction temperature. Preferably, the reaction temperature is in a range of from 100 °C - 300 °C. When vinyl acetate is produced as the alkenyl acetate, the reaction temperature is preferably in the range of from 120 °C - 250 °C.

The reaction pressure is preferably 0-30 bar, and more preferably 1 - 10 bar, wherein the reaction pressure is measured as gauge pressure. Gauge pressure is zero referenced against ambient air pressure.

The reaction may be conducted in any manner known to the skilled person, such as using a fixed bed or fluidized bed. However, a fixed bed flow reaction is preferred. Selectivity is defined as

C₂H₄ selectivity [%] = ¹⁰⁰

STY is defined as

g VAM/h VAM m

STY

I catalyst catalyst volume [I] EXAMPLES

All chemicals are used as received without further treatment. S1O2 spherical support is purchased from Clariant (KA-160).

1.1 Electroless deposition of Au on Pd/SiC

Example 1 : NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Na2PdCU is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. The NaOH solution is impregnated first by spraying onto 96 g of S1O2 of spherical support of 5 mm diameter in an impregnation drum. In addition, the Pd solution (T = 25 °C) is sprayed onto the wet support within 3 minutes as described above. The impregnated support material is aged for 5 h followed by washing with 5 L of de-ionised water for 36 h. The Pd/Si02 catalyst is dried at 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2 and N2H4 is mixed with de-ionised water, resulting in 60 mL of Au solution. The Au solution is sprayed onto the Pd-plated support as described above. The impregnated material is aged for 5 h, and dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%. Reaction conditions and performance of examples 1.1 - 1.15 in VAM production are shown in Table 1.

Example 2: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Na2PdCU is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. Second, Pd solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Pd/Si02, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Pd/Si02 catalyst is dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 300 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 are mixed with de-ionised water, resulting in 60 mL of Au solution. The Au solution is impregnated by spraying onto Pd/Si02 prepared earlier as described above. The impregnated material is aged for 5 h, and dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.6 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%. Example 3: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Pd(OH)2 is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. Second, Pd solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Pd/SiCh, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Pd/SiCh catalyst is dried at 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 are mixed with de-ionised water, resulting in 60 mL of Au solution. The Au solution is impregnated by spraying onto Pd/SiCh prepared earlier as described above. The impregnated material is aged for 5 h, and dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.8 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%.

Example 4: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Na2PdCU is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. Second, Pd solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Pd/Si02, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Pd/Si02 catalyst is dried at 110 ⁰ until moisture content is less than 5 wt%. 0.6 g of N2H4 is diluted to 60 mL with de-ionised water, the solution is impregnated by spraying onto Pd/Si02 as described above. The Pd/Si02 catalyst is dried at 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 are mixed with de-ionised water, resulting in 60 mL of Au solution. The Au solution is impregnated by spraying onto Pd/Si02 prepared earlier as described above. The impregnated material is aged for 5 h, and dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 300 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.8 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%. Reaction conditions and performance in VAM production are shown in Table 1.

Example 5: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Na2PdCU is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. Second, Pd solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Pd/Si02, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Pd/Si02 catalyst is dried at 110 °C until moisture content is less than 5 wt%. 0.12 g of N2H4 is diluted to 60 mL with de-ionised water, the solution is impregnated by spraying onto Pd/Si02 as described above._The Pd/Si02 catalyst is dried at 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 is mixed with de-ionised water, resulting in 60 imL of Au solution. The Au solution is impregnated by spraying onto Pd/SiCh prepared earlier as described above. The impregnated material is aged for 5 h, and dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 300 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.8 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%. Reaction conditions and performance in VAM production are shown in Table 1.

Example 6: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Na2PdCU is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. Second, Pd solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Pd/SiCh, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Pd/SiCh catalyst is dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 200 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 are mixed with de-ionised water, resulting in 60 mL of Au solution. The Au solution is impregnated by spraying onto Pd/SiCh prepared earlier as described above. The impregnated material is aged for 5 h, and dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 300 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.8 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%.

Example 7: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Na2PdCU is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. Second, Pd solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Pd/Si02, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Pd/Si02 catalyst is dried at 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 are mixed with de-ionised water, resulting in 60 mL of Au solution. The Au solution (T = 85 °C) is impregnated by spraying onto Pd/Si02 prepared earlier as described above. The impregnated material is aged for 5 h, and dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 200 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 3 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%.

Example 8: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Na2PdCU is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. Second, Pd solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Pd/SiCh, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Pd/SiCh catalyst is dried at 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 are mixed with de-ionised water, resulting in 60 mL of Au solution. The Au solution (T = 85 °C) is impregnated by spraying onto Pd/SiCh prepared earlier as described above. The impregnated material is aged for 5 h, and dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 400 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.8 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%.

Example 9: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Na2PdCU is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. Second, Pd solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Pd/SiCh, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Pd/SiCh catalyst is dried at 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 is mixed with de-ionised water, resulting in 60 mL of Au solution. The Au solution (T = 85 °C) is impregnated by spraying onto Pd/SiCh prepared earlier as described above. The impregnated material is aged for 5 h, and dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.8 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%.

Example 10: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Na2PdCU is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. Second, Pd solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Pd/Si02, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Pd/Si02 catalyst is dried at 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 are mixed with excess of de-ionised water, resulting in 2000 mL of Au solution. The Au solution (T = 25 °C) is brought into contact with Pd/Si02 resulting in a slurry that is stirred for 24 h. The material is filtered and dried at 85 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 3 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%.

Example 11 : 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 1 g of Pd as Na2PdCU is mixed with de-ionised water, resulting in a solution of 30 mL Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. Second, Pd solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Pd/SiCh, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Pd/SiCh catalyst is dried at 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 are mixed with excess of de-ionised water, resulting in 2000 mL of Au solution. The Au solution (T = 85 °C) is brought into contact with

Pd/Si02 resulting in a slurry that is stirred for 24 h. The material is filtered and dried at 85 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 3 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%.

1.2 Electroless deposition of Pd on Au/SiCh

Example 12: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 0.5 g of Au as HAuCU is mixed with de-ionised water, resulting in a solution of 30 mL Au solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum.

Second, Au solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. Au/SiCh, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The Au/SiCh catalyst is dried at 110 °C until moisture content is less than 5 wt%. 1 g of Pd as Na₂PdCI₄, 0.72 g of NhUOH, 1.8 g of Na₂H₂P02, and 0.6 g of Na₂EDTA are mixed with de-ionised water, resulting in 60 mL of Pd solution. The Pd solution is impregnated by spraying onto the Au-plated support as described above. The impregnated material is aged for 5 h, and dried at T = 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.6 g of potassium is impregnated onto the catalyst and the wet catalyst is dried at T = 110 °C until moisture content is less than 5 wt%.

Example 13: 2.3 g of NaOH is dissolved in de-ionised water, resulting in 30 mL of NaOH solution. 0.5 g of Au as HAuCU is mixed with de-ionised water, resulting in a solution of 30 mL Au solution. 96 g of S1O2 spherical support of 5 mm diameter are first impregnated with the NaOH solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum.

Second, Au solution is impregnated by spraying onto the wet support as described above. The impregnated support material, i.e. AU/S1O2, is aged for 5 h followed by washing with 5 L of de- ionised water for 36 h. The AU/S1O2 catalyst is dried at 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 200 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. 1 g of Pd as Na₂PdCI₄, 0.72 g of NH₄OH, 1.8 g of Na₂H₂P0₂, and 0.6 g of Na₂EDTA is mixed with de-ionised water, resulting in 60 mL of Pd solution. The Pd solution is impregnated by spraying onto the Au- plated support as described above. The impregnated material is aged for 5 h, and dried at T = 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.6 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at T = 110 °C until moisture content is less than 5 wt%. 1.3 Electroless deposition of Pd on S1O2 followed by electroless deposition of Au

Example 14: 1 g of Pd as Na₂PdCI₄, 0.72 g of NhUOH, 1.8 g of Na₂H₂P02, and 0.6 g of Na₂EDTA are mixed with de-ionised water, resulting in 60 mL of Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are impregnated with the Pd solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. The impregnated material is aged for 5 h, and dried at T = 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2, and 0.12 g of N2H4, are mixed with de-ionised water, resulting in 60 mL of Au solution. The Au solution is impregnated onto the Pd-plated support as described above. The impregnated material is aged for 5 h, and dried at T = 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.6 g of potassium is impregnated onto the catalyst as described above and the wet catalyst is dried at 110 °C until moisture content is less than 5 wt%.

Example 15: 1 g of Pd as Na₂PdCI₄, 0.72 g of NhUOH, 1.8 g of Na₂H₂P02, 0.6 g of Na₂EDTA are mixed with de-ionised water, resulting in 60 mL of Pd solution. 96 g of S1O2 spherical support of 5 mm diameter are impregnated with the Pd solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. The impregnated material is aged for 5 h, and dried at T = 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 300 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. 0.5 g of Au as KAu(CN)₂, 0.12 g of N2H4, is mixed with de-ionised water, resulting in 60 mL of Au solution. The Au solution is impregnated onto the Pd-plated support as described above. The impregnated material is aged for 5 h, and dried at

T = 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.6 g of potassium is impregnated onto the catalyst as described above and the wet catalyst is dried at T = 110 °C until moisture content is less than 5 wt%.

1.4 Electroless deposition of Au on S1O2 followed by deposition of Pd

Example 16: 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 are mixed with excess of de-ionised water, resulting in 2000 mL of Au solution. 96 g of S1O2 spherical support with 5 mm diameter are impregnated with the Au solution by spraying the solution (T = 25 °C) onto the support within 3 minutes in an impregnation drum. The impregnated material is aged for 5 h, and dried at

T = 110 °C until moisture content is less than 5 wt%. 1.12 g of NhUOH, 3.96 g of NhUCI, and 1.48 g of ΝΘΣΗΣΡΟΣ are mixed with de-ionised water, resulting in 30 mL of solution. 1 g of Pd as Na2PdCU is dissolved in de-ionised water, resulting in 30 mL of Pd solution. Both solutions are impregnated sequentially as described above, resulting in Pd-sol being later onto Au/SiCh catalyst. The impregnated material is aged for 5 h, and dried at T = 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.6 g of potassium is impregnated onto the catalyst as described above and the wet catalyst is dried at T = 110 °C until moisture content is less than 5 wt%.

Example 17: (fixing agent (Nh COs) 1.5 g of (Nh CCh is diluted with de-ionised water up to 300 mL solution. This solution (T = 25 °C) is brought into contact with 96 g of S1O2 spherical support with 5 mm diameter under stirring for 1 h resulting in a slurry. The impregnated material is aged for 5 h, and dried at T = 110 °C until moisture content is less than 5 wt%. 0.5 g of Au as KAu(CN)2 and 0.12 g of N2H4 are mixed with excess of de-ionised water, resulting in 2000 mL of Au solution. The Au solution (T = 25 °C) is sprayed onto above obtained support within 3 minutes in an impregnation drum. The impregnated material is aged for 5 h, and dried at T = 110 °C until moisture content is less than 5 wt%. 1.12 g of NhUOH, 3.96 g of NhUCI, and 1.48 g of Na₂H₂P02 are mixed in de-ionised water, resulting in 30 mL of solution. 1 g of Pd as Na2PdCU is diluted to 30 mL of solution. Both solutions are impregnated sequentially by spraying as described above, resulting in Pd-sol being later onto Au/SiCh catalyst. The impregnated material is aged for 5 h, and dried at T = 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 600 °C for 1 h in 1 L/min 5 % H2 N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.6 g of potassium is impregnated onto the catalyst by spraying as described above and the wet catalyst is dried at T = 110 °C until moisture content is less than 5 wt%.

1.5 Simultaneous electroless deposition of Au and Pd on S1O2

Example 18: 0.45 g of Au as AuCIs, 1 g of Pd as PdCI₂, 1.12 g of NhUOH, 3.96 g of NhUCI, and 1.48 g of ΝΘΣΗΣΡΟΣ are mixed in excess of de-ionised water, resulting in 2000 mL of Au/Pd- solution. The Au/Pd solution (T = 25 °C) is brought into contact with 96 g of S1O2 support under stirring for 24 h resulting in a slurry. The material is filtered and aged for 5 h, and dried at

T = 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 300 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.6 g of potassium is impregnated by spraying the solution (T = 25 °C) onto the catalyst within 3 minutes in an impregnation drum and the wet catalyst is dried at T = 110 °C until moisture content is less than 5 wt%.

Example 19: 0.5 g of Au as HAuCU, 1 g of Pd as PdCI₂, 0.72 g of NhUOH, 0.05 g KCN, 1.8 g of ΝΘΣΗΣΡΟΣ, and 0.6 g of Na2EDTA are mixed in excess of de-ionised water, resulting in 2000 mL of Au/Pd solution. The Au/Pd solution (T = 25 °C) is brought into contact with 96 g of S1O2 support under stirring for 24 h resulting in a slurry. The material is filtered and aged 5 h, and dried at

T = 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 300 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.6 g of potassium is impregnated by spraying the solution (T = 25 °C) onto the catalyst within 3 minutes in an impregnation drum and the wet catalyst is dried at T = 110 °C until moisture content is less than 5 wt%. Example 20: 0.36 g of Au as HAuCU, 1 g of Pd as Pd(OH)₂, 0.72 g of NhUOH, 1.8 g of Na₂H₂P02, 2.4 g of N2H4, and 0.6 g of Na2EDTA are mixed in excess of de-ionised water, resulting in 2000 mL of Au-Pd solution. The Au-Pd solution (T = 25 °C) is brought into contact with 96 g of S1O2 support under stirring for 24 h resulting in a slurry. The material is filtered and aged for 5 h, and dried at T = 110 °C until moisture content is less than 5 wt%. The dried catalyst is reduced at 300 °C for 1 h in 1 L/min 5 % H2/N2 gas flow. Further, 60 mL of potassium acetate solution containing 2.6 g of potassium is impregnated by spraying the solution (T = 25 °C) onto the catalyst within 3 minutes in an impregnation drum and the wet catalyst is dried at T = 110 °C until moisture content is less than 5 wt%.

2. Comparative examples

Comparative example 1 (CE 1 ): The Au-Pd bimetallic powder catalyst is prepared according to Catalysis Today 160 (2011 ) 170-178 and Journal of Catalysis 270 (2010) 224-233. Comparative example 2 (CE 2): The Au-Pd bimetallic catalyst is prepared according to comparative example 1 of US5808136.

3. Reaction conditions for VAM production

Fixed bed reactor; Catalyst volume = 20 mL; Inert glas beads = 180 mL;

Feed composition for all examples:

Acetic acid 17 vol%, Ethylene 63 vol%, Oxygen 5.7 vol%, Balance nitrogen,

Total Flow rate = 1750 SCCM (standard cubic centimeter per minute),

T = 150 °C, p = 5 bar, Runtime = 20 h

Table 1 : Reaction conditions and results in VAM production.

Table 2: Results in VAM production of comparative examples.

4. Metal leaching

Table 3: Metal leaching in water.

c(M) = sum of Pd and Au

The metal concentration is measured by ICP-OES methods.

As can be seen from table 3 the metal leaching of the Au-Pd bimetallic shell-type catalyst prepared according to the present invention is very low and comparable to known Au-Pd bimetallic catalysts.

Claims

1. A process for the preparation of a Au-Pd bimetallic shell-type catalyst, comprising the following steps

a. providing a solid, shaped body catalyst support,

b. contacting the support with two solutions,

one solution containing Au ions in an amount of from 0.1-10 wt% and

the other solution containing Pd ions in an amount of from 0.1-10 wt%,

e. drying to obtain the Au-Pd bimetallic shell-type catalyst.

2. The process according to claim 1 , wherein

the support is first contacted with a solution containing ions of a first metal, wherein the first metal is selected from gold and palladium to obtain a plated support comprising gold or palladium,

this support is aged, washed and dried before contacting it with a solution containing ions of a second metal, wherein the second metal is palladium when the first metal is gold and that is gold when the first metal is palladium, to obtain a plated support comprising gold and palladium,

this support is aged and dried, before being reduced according to step c) of claim 1.

3. The process according to claim 1 or 2, wherein the first metal is Pd and the second metal is Au, wherein the solution containing palladium is an aqueous solution of Na2PdCU and N2H4, and the molar ratio of Na₂PdCI₄ : N2H4 is 1 :1 - 1 :30.

4. The process according to claim 1 or 2, wherein the first metal is Pd and the second metal is Au , wherein the solution containing gold is an aqueous solution comprising of KAu(CN)2 and N2H4, and the molar ratio of KAu(CN)₂ : N2H4 is 1 :1 - 1 :30.

5. The process according to claim 3 or 4, wherein the plated support comprising palladium is reduced in liquid phase or gas phase before the deposition of Au.

6. The process according to claim 1 or 2, wherein the first metal is Au and the second metal is Pd, wherein the solution containing palladium is an aqueous solution of Na2PdCU and N2H4, the molar ratio of Na₂PdCl4 : N2H4 being 1 :1 - 1 :30.

7. The process according to claim 1 or 2, wherein the first metal is Au and the second metal is Pd, wherein the solution is an aqueous solution of KAu(CN)2 and N2H4, the molar ratio of

KAu(CN)₂ : N2H4 being 1 :1 - 1 :30.

8. The process according to claim 6 or 7, wherein the plated support is reduced in liquid phase or gas phase before the deposition of Pd.

9. A process for the preparation of a Au-Pd bimetallic shell-type catalyst, comprising the following steps:

a. providing a precious metal catalyst containing 0.1-10 wt-% of a first metal selected from palladium and gold on a solid, shaped body support,

e. drying to obtain the Au-Pd bimetallic shell-type catalyst.

10. A process for the preparation of a Au-Pd bimetallic shell-type catalyst, comprising the

following steps:

a. providing a solid, shaped body catalyst support,

b. contacting the support with a solution containing ions of Au and Pd, wherein the amount of Au in the solution is in the range of from 0.1-10 wt% and of

Pd in the solution is in the range of from 0.1-10 wt%,

with the proviso that the weight ratio of Pd:Au is in the range of from 0.2:1 to 4:1 , c. reducing the plated support with hydrogen to obtain the Au-Pd bimetallic shell-type pre- catalyst,

d. contacting the Au-Pd bimetallic pre-catalyst with an aqueous potassium acetate solution with a content of potassium in the range of from 0.1-10 wt%

e. drying to obtain the Au-Pd bimetallic shell-type catalyst

11. The process according to claims 1 to 10, wherein the pH of the solution containing Pd ions and/or the solution containing Au ions is 8 -12.

12. The process according to claims 1 to 11 , wherein the solution containing Pd ions and/or the solution containing Au ions further comprises hydrazine, formaldehyde, dimethylamine borane (DMAB) and/or sodium borohydride.

13. The process according to claim 1 to 12, wherein the catalyst support material is selected from the group consisting of silica, alumosilicate, titania, alumina, zirconia, yttria, and mixtures thereof.

14. The process according to claim 1 to 13, wherein the catalyst support is in the form of

spheres, extrudates, cut extrudates, trilobes, stars, rings, cylinders, or pellets.

15. A process for the production of alkenyl acetates, wherein a Au-Pd bimetallic catalyst is

applied that is prepared according to a process of anyone of claims 1 to 14.

16. The process according to claim 15, wherein the alkenyl acetate is vinyl acetate.