Platinum catalysts from in situ formed platinum dioxide
A carbon-supported platinum catalyst obtained by chemical reduction of in situ-formed platinum dioxide on a carbon support and a method of production thereof.
1. A method for the production of a carbon-supported platinum catalyst comprising:
(i) formation of platinum dioxide on a carbon support in an aqueous solution, said platinum dioxide being in situ-formed from of dihydrogen-hexahydroxyplatinate in an acidic solution by variation of the pH between 2 and 5 and/or temperature between 30 and 100° C. and said carbon support slurried in a non-complexing strong acid,
(ii) chemically reducing in situ-formed platinum dioxide on a carbon support in an aqueous solution, with a reducing agent selected from the group consisting of formaldehyde, formic acid, oxalic acid, sodium borohydride and hypophosphite
(iii) performing a thermal treatment in a controlled atmosphere between 120 and 500° C.
2. The method of claim 1 wherein said in situ formation of platinum dioxide is obtained by converting a dihydrogen hexahydroxyplatinate precursor pre-adsorbed on said carbon support.
3. The method of claim 1 wherein said variation of pH is obtained by the addition of caustic soda or ammonia.
4. The method of claim 3 wherein said addition of caustic soda or ammonia is effected up to a pH between 2 and 5.
5. The method of claim 1 wherein said variation of temperature consists of bringing said aqueous solution from room temperature to a final temperature of 30 to 100° C.
6. The method of claim 1 wherein said carbon support is a carbon black having an active area not lower than 50 m 2 /g.
7. The method of claim 6 wherein said carbon black is slurried in a strong acid selected from the group consisting of HNO 3 , HC 1 O 4 , CF 3 COOH, toluenesulfonic acid, trifluoromethanesulfonic acid, HCl, HBr, prior to the adsorption of said dihydrogen hexahydroxyplatinate precursor.
8. The method of claim 7 wherein said variation of pH is obtained by the addition of caustic soda or ammonia.
9. The method of claim 8 wherein said addition of caustic soda or ammonia is effected up to a pH between 2 and 5.
10. The method of claim 1 wherein said controlled atmosphere is a reducing atmosphere or an inert atmosphere.
11. A method for the production of a platinum black catalyst comprising chemically reducing platinum dioxide formed in situ by conversion of dihydrogen-hexahydroxyplatinate from an acidic solution by variation of the pH between 2 and 5 and/or temperature between 30 and 100° C.
12. The method of claim 11 wherein said variation of temperature consists of bringing said aqueous solution from room temperature to a final temperature of 30 to 100° C.
13. A method for the production of a carbon-supported platinum catalyst comprising:
(i) formation of platinum dioxide on a carbon support in an aqueous solution, said platinum dioxide being in situ-formed from of dihydrogen-hexahydroxyplatinate in an acidic solution by variation of the pH between 2 and 5 and/or temperature between 30 and 100° C. and said carbon support slurried in a non-complexing strong acid,
(ii) chemically reducing in situ-formed platinum dioxide on a carbon support in a reducing agent selected from the group consisting of hydrogen gas during a thermal treatment in a controlled atmosphere between 120 and 500° C.