Preparation of palladium-gold catalysts

1. A method for preparing a supported palladium-gold catalyst, said method comprising

(a) increasing a titanium dioxide support intrusion volume to greater than or equal to 0.31 milliliter of mercury per gram by mixing two titanias which have different sizes, or by mixing a sintered titania with a non-sintered titania, or by mixing a spray-dried titania with a non-spray dried titania; impregnating the support with a palladium salt, gold salt, and an optional alkali metal or ammonium compound; and

(b) reducing the impregnated support to form the supported palladium-gold catalyst.

2. The method of claim 1 , wherein the titanium dioxide support has a total intrusion volume of greater than or equal to 0.35 milliliter per gram.

3. The method of claim 1 , wherein the titanium dioxide support has a total intrusion volume of greater than or equal to 0.40 milliliter per gram.

4. The method of claim 1 , wherein the alkali metal or ammonium compound in selected from the group consisting of hydroxides, carbonates, bicarbonates, metasilicates, and mixtures thereof.

5. The method of claim 1 , wherein the alkali metal or ammonium compound is a carbonate or bicarbonate.

6. The method of claim 1 , wherein the palladium salt is selected from the group consisting of palladium chloride, sodium chloropalladite, palladium nitrate, and palladium sulfate; and the gold salt is selected from the group consisting of auric chloride, tetrachloroauric acid, sodium tetrachloroaurate, and mixtures thereof

7. A method for preparing a supported palladium-gold catalyst, said method comprising

(a) increasing a titanium dioxide support intrusion volume to greater than or equal to 0.31 milliliter of mercury per gram by mixing two titanias which have different sizes, or by mixing a sintered titania with a non-sintered titania, or by mixing a spray-dried titania with a non-spray dried titania; impregnating the support with a palladium salt, gold salt, and an alkali metal or ammonium compound;

(b) calcining the impregnated support; and

(c) reducing the calcined support to form the supported palladium-gold catalyst.

8. The method of claim 7 , wherein the calcination is performed in a non-reducing atmosphere at a temperature within the range of 100° C. to 600° C.

9. The method of claim 8 , wherein the non-reducing atmosphere is selected from the group consisting of helium, nitrogen, argon, neon, nitrogen oxides, oxygen, air, carbon dioxide, and mixtures thereof.

10. The method of claim 9 , wherein the calcination temperature is within the range of 100° C. to 300° C.

11. The method of claim 7 , wherein the reduction is performed in the presence of hydrogen.

12. The method of claim 11 , wherein the reduction is performed at a temperature within the range of 300° C. to 600° C.

13. The method of claim 11 , wherein the reduction is performed at a temperature within the range of 450° C. to 550° C.

14. The method of claim 7 , which farther comprises (d) treating the supported palladium-gold catalyst with a potassium salt.

15. A method for preparing a supported palladium-gold catalyst, said method comprising

(a) increasing a titanium dioxide support intrusion volume to greater than or equal to 0.31 milliliter of mercury per gram by mixing two titanias which have different sizes, or by mixing a sintered titania with a non-sintered titania, or by mixing a spray-dried titania with a non-spray dried titania; calcining the titanium dioxide support;

(b) impregnating the calcined support with a palladium salt, a gold salt, and an alkali metal or ammonium compound;

(c) calcining the impregnated support; and

(d) reducing the calcined support from step (c) to form the supported palladium-gold catalyst.

16. The method of claim 15 , wherein the titanium dioxide support has a total intrusion volume of greater than or equal to 0.35 milliliter of mercury per gram.

17. The method of claim 15 , wherein the titanium dioxide support has a total intrusion volume of greater than or equal to 0.40 milliliter of mercury per gram.