Processes for the manufacturing of oxidation catalysts
Disclosed are catalysts comprised of platinum and gold. The catalysts are generally useful for the selective oxidation of compositions comprised of a primary alcohol group and at least one secondary alcohol group wherein at least the primary alcohol group is converted to a carboxyl group. More particularly, the catalysts are supported catalysts including particles comprising gold and particles comprising platinum, wherein the molar ratio of platinum to gold is in the range of about 100:1 to about 1:4, the platinum is essentially present as Pt(0) and the platinum-containing particles are of a size in the range of about 2 to about 50 nm. Also disclosed are methods for the oxidative chemocatalytic conversion of carbohydrates to carboxylic acids or derivatives thereof. Additionally, methods are disclosed for the selective oxidation of glucose to glucaric acid or derivatives thereof using catalysts comprising platinum and gold. Further, methods are disclosed for the production of such catalysts.
1. A process for manufacturing an oxidation catalyst comprising the steps of:
a) mixing a support with an aqueous solution comprising at least one gold-containing compound to form a slurry,
b) adding a base to the slurry to form an insoluble gold complex which deposits on the surface of the support thereby forming a gold-containing support,
c) heating the gold-containing support,
d) mixing the gold-containing support from step c) with an aqueous solution or a colloid comprising at least one platinum-containing compound to impregnate the gold-containing support with the platinum-containing compound,
e) drying the resulting impregnated support from step d) at a temperature up to about 120° C., and
f) reducing platinum on the dried impregnated support from step e) at a temperature in the range of from about 200° C. to about 600° C. to produce the oxidation catalyst, wherein the oxidation catalyst comprises particles comprising gold and particles comprising platinum on the support, the molar ratio of platinum to gold of the catalyst is in the range of from about 100:1 to about 1:4, the platinum is substantially present on the support as Pt(0), and the particle sizes of the particles comprising platinum are substantially in the range of from about 2 to about 50 nanometer, and wherein the catalyst has the ability to catalyze oxidation of glucose to glucaric acid.
2. The process of claim 1 further comprising collecting the gold-containing support prior to the heating of step c).
3. The process of claim 2 wherein collecting the gold-containing support comprises centrifugation.
4. The process of claim 1 wherein the gold-containing support is heated in step c) at a temperature sufficient to dry the support.
5. The process of claim 1 wherein the gold-containing support is heated in step c) at a temperature sufficient to reduce the gold on the support to Au(0).
6. The process of claim 1 wherein the gold-containing support is heated in step c) in a reducing atmosphere comprising hydrogen gas.
7. The process of claim 1 wherein gold on the dried impregnated support is reduced in step f).
8. The process of claim 1 wherein reducing the platinum on the dried impregnated support is conducted in a reducing atmosphere comprising hydrogen gas.
9. The process of claim 8 wherein the reducing atmosphere further comprises nitrogen gas.
10. The process of claim 1 wherein reducing the platinum on the dried impregnated support is conducted at a temperature in the range of from about 200° C. to about 400° C.
11. The process of claim 1 wherein the resulting impregnated support from step d) is dried at a temperature in the range of from about 40° C. to about 80° C.
12. The process of claim 1 wherein the support comprises a material selected from the group consisting of carbon, aluminas, silicas, titanias, zirconias, zeolites, montmorillonites, and modifications and combinations thereof.
13. The process of claim 1 wherein the support comprises a material selected from the group consisting of titanias, zirconias, silicas, and combinations thereof.
14. The process of claim 1 wherein the support comprises titania.
15. The process of claim 1 wherein the support comprises zirconia.
16. The process of claim 1 wherein the total metal loading of the catalyst is about 10 wt % or less.
17. The process of claim 1 wherein the total metal loading of the catalyst is from about 1 to about 8 wt %.
18. The process of claim 1 wherein the particles sizes of the particles comprising platinum are substantially in the range of from about 5 to about 20 nanometers.
19. The process of claim 1 wherein at least about 50% of the particles comprising platinum have a size from about 8 to about 12 nanometers.
20. The process of claim 1 wherein the particle sizes of the particles comprising gold are substantially in the range of from about 2 to about 20 nanometers.
21. The process of claim 1 wherein at least about 50% of the particles comprising gold have a size from about 5 to about 12 nanometers.
22. The process of claim 1 wherein the molar ratio of platinum to gold of the catalyst is from about 10:1 to about 1:4.
23. The oxidation catalyst prepared by the process of claim 1 .