Claims
- 1. In a process for the preparation of a supported palladium-gold catalyst wherein an inert support is impregnated with palladium and gold salts and the salts subsequently reduced to the corresponding metals, to produce catalysts having increased selectivity and activity for the vapor phase production of vinyl acetate by the reaction of ethylene, acetic acid and oxygen, the improvement comprising calcining the impregnated support having the palladium and gold salts deposited thereon by heating in a non-reducing atmosphere at a temperature from about 100.degree. C. to about 600.degree. C. to effect decomposition of at least 10 percent of the palladium and gold salts before reducing the palladium and gold to the metallic state.
- 2. The process of claim 1 wherein the supported palladium-gold catalyst contains from 0.1 to 3 weight percent palladium, from 0.1 to 3 weight percent gold and the weight ratio of palladium to gold is from 5:1 to 1:3.
- 3. The process of claim 2 wherein the inert support has a pore volume from 0.1 to 0.75 cc/g and surface area is from 0.5 to 500 m.sup.2 /g.
- 4. The process of claim 3 wherein the inert support is selected from the group consisting of alumina, silica, silica-alumina and titania, the catalyst contains 0.5 to 1.5 weight percent palladium and 0.25 to 0.75 weight percent gold and the weight ratio of palladium to gold is from 2.5:1 to 1:1.5.
- 5. The process of claim 4 wherein the inert support has a pore volume from 0.2 to 0.65 cc/g and surface area from 1 to 200 m.sup.2 /g.
- 6. The process of claim 5 wherein the inert support is alumina having a surface area from 2 to 50 m.sup.2 /g and alpha-alumina content greater than 95 percent.
- 7. The process of claim 5 wherein the inert support is silica or silica-alumina having a surface area from 30 to 200 m.sup.2 /g.
- 8. The process of claim 1 wherein the non-reducing atmosphere is an inert or oxidizing gas selected from the group consisting of helium, nitrogen, argon, neon, nitrogen oxides, oxygen, air and carbon dioxide.
- 9. The process of claim 8 wherein the palladium and gold are reduced at a temperature from ambient to 550.degree. C. and the reducing agent is selected from the group consisting of ammonia, carbon monoxide, hydrogen, hydrocarbons, olefins, aldehydes, alcohols, hydrazine, primary amines, carboxylic acids, carboxylic acid salts and carboxylic acid esters.
- 10. The process of claim 9 wherein the impregnated support is calcined at a temperature from 350 to 600.degree. C. and 70 percent or more of the palladium and gold salts are decomposed.
- 11. The process of claim 10 wherein the reducing agent is hydrogen or a mixture of hydrogen with an inert gas and the temperature of reduction is 100 to 550.degree. C.
- 12. The process of claim 11 wherein the impregnated support is calcined at 400 to 550.degree. C.
- 13. The process of claim 12 wherein the temperature of reduction is 350 to 525.degree. C.
- 14. The process of claim 9 wherein the impregnated support is calcined at a temperature up to 350.degree. C. and 10 to 70 percent of the palladium and gold salts are decomposed.
- 15. The process of claim 14 wherein the reducing agent is hydrogen or a mixture of hydrogen and an inert gas and the temperature of reduction is 100 to 550.degree. C.
- 16. The process of claim 15 wherein the temperature of reduction is 150 to 525.degree. C.
- 17. The process of claim 15 wherein the impregnated support is calcined at 150 to 275.degree. C. and reduced while increasing the temperature from 150 to 275.degree. C. up to 475 to 525.degree. C. at a rate of 0.1 to 25.degree. C. per minute.
- 18. A process for the production of a supported palladium-gold catalyst containing from 0.1 to 3 weight percent palladium, 0.1 to 3 weight percent gold and having a weight ratio of palladium to gold from 5:1 to 1:3 comprising:
- (1) impregnating an inert support selected from the group consisting of alumina and titania and having a pore volume from 0.1 to 0.75 cc/g and surface area from 0.5 to 500 m.sup.2 /g with palladium and gold salts by contacting said support with an aqueous solution of an alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate or alkali metal metasilicate to fill from 25 to 95 percent of the absorptive capacity of the support and thereafter with an aqueous solution of tetrachloroauric acid and palladium chloride or sodium chloropalladite to effect essentially complete precipitation of the palladium and gold salts;
- (2) drying to remove water;
- (3) calcining by heating in an inert or oxidizing gas selected from the group consisting of helium, nitrogen, argon, neon, nitrogen oxides, oxygen, air and carbon dioxide at a temperature from 100 to 350.degree. C. to decompose from 10 to 70 percent of the palladium and gold salts; and
- (4) reducing in hydrogen or a mixture of hydrogen and an inert gas at a temperature from 100 to 550.degree. C. to convert the palladium and gold to the metallic state.
- 19. The process of claim 18 wherein the calcination is conducted at a temperature from 150 to 275.degree. C. and the reduction is carried out while increasing the temperature from 150 to 275.degree. C. up to 475 to 525.degree. C. at a rate of 0.1 to 25.degree. C. per minute.
- 20. The process of claim 18 wherein the catalyst is activated by treating with 1 to 15 weight percent solution of an alkali metal carboxylate, alkali metal hydroxide or mixture thereof.
- 21. The process of claim 20 wherein the catalyst is activated by treating with an aqueous solution containing 1 to 15 weight percent potassium acetate and up to 5 weight percent potassium hydroxide.
- 22. The process for the production of a supported palladium-gold catalyst containing from 0.1 to 3 weight percent palladium and 0.1 to 3 weight percent gold and having a weight ratio of palladium to gold from 5:1 to 1:3 comprising:
- (1) impregnating an inert support selected from the group consisting of silica and silica-alumina and having a pore volume from 0.1 to 0.75 cc/g and surface area from 0.5 to 500 m.sup.2 /g with palladium and gold salts by contacting said support with an aqueous solution of tetrachloroauric acid and palladium chloride or sodium chloropalladite to essentially completely fill the absorptive capacity of the support and thereafter with an aqueous solution of an alkali metal carbonate to effect essentially complete precipitation of the palladium and gold salts;
- (2) drying to remove water;
- (3) calcining by heating in an inert or oxidizing gas selected from the group consisting of helium, nitrogen, argon, neon, nitrogen oxides, oxygen, air and carbon dioxide at a temperature from 100 to 350.degree. C. to decompose from 10 to 70 percent of the palladium and gold salts; and
- (4) reducing in hydrogen or a mixture of hydrogen and an inert gas at a temperature from 100 to 550.degree. C. to convert the palladium and gold to the metallic state.
- 23. The process of claim 22 wherein the calcination is conducted at a temperature from 150 to 275.degree. C. and the reduction is carried out while increasing the temperature from 150 to 275.degree. C. up to 475 to 525.degree. C. at a rate of 0.1 to 25.degree. C. per minute.
- 24. The process of claim 22 wherein the catalyst is activated by treating with 1 to 15 weight percent solution of an alkali metal carboxylate.
- 25. The process of claim 24 wherein the catalyst is activated by treating with an aqueous solution containing 1 to 4 weight percent potassium acetate.
- 26. A process for the production of a supported palladium-gold catalyst containing from 0.1 to 3 weight percent palladium, 0.1 to 3 weight percent gold and having a weight ratio of palladium to gold from 5:1 to 1:3 comprising:
- (1) impregnating an inert support selected from the group consisting of alumina, silica, silica-alumina and titania and having a pore volume from 0.1 to 0.75 cc/g and surface area from 0.5 to 500 m.sup.2 /g with palladium and gold salts by contacting said support with an aqueous solution of an alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate or alkali metal metasilicate to fill from 25 to 95 percent of the absorptive capacity of the support and thereafter with an aqueous solution of tetrachloroauric acid and palladium chloride or sodium chloropalladite to effect essentially complete precipitation of the palladium and gold salts;
- (2) drying to remove substantially all associated water;
- (3) calcining by heating in an inert or oxidizing gas selected from the group consisting of helium, nitrogen, argon, neon, nitrogen oxides, oxygen, air and carbon dioxide at a temperature from 350 to 600.degree. C. to decompose 70 percent or more of the palladium and gold salts; and
- (4) reducing in hydrogen or a mixture of hydrogen and an inert gas at a temperature from 100 to 550.degree. C. to convert the palladium and gold to the metallic state.
- 27. The process of claim 26 wherein the impregnated support is calcined at a temperature from 400 to 550.degree. C. and reduced at a temperature from 350 to 525.degree. C.
- 28. The process of claim 26 wherein the catalyst is activated by treating with 1 to 15 weight percent solution of an alkali metal carboxylate, alkali metal hydroxide or mixture thereof.
- 29. A supported palladium-gold catalyst obtained by the process of any one of the preceding claims.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional application Ser. No. 60/011,586 filed Nov. 7, 1995 and U.S. Provisional application Ser. No. 60/019,811 filed Jun. 12, 1996.
US Referenced Citations (5)
Foreign Referenced Citations (2)
Number |
Date |
Country |
1269113 |
May 1968 |
DEX |
60-171271 |
Sep 1985 |
JPX |