Low Temperature Water–gas Shift: Differences in Oxidation States Observed with Partially Reduced Pt/MnOX and Pt/CeOX Catalysts Yield Differences in OH Group Reactivity
The Pt-ceria synergy may be described as the dehydrogenation of formate formed on the surface of the partially reducible oxide (PRO), ceria, by Pt across the interface, with H{sub 2}O participating in the transition state. However, due to the rising costs of rare earth oxides like ceria, replacement by a less expensive partially reducible oxide, like manganese oxide, is desirable. In this contribution, a comparison between Pt/ceria and Pt/manganese oxide catalysts possessing comparable Pt dispersions reveals that there are significant differences and certain similarities in the nature of the two Pt/PRO catalysts. With ceria, partial reduction involves reduction of the oxide surface shell, with Ce{sup 3+} at the surface and Ce{sup 4+} in the bulk. In the case of manganese oxide, partial reduction results in a mixture of Mn{sup 3+} and Mn{sup 2+}, with Mn{sup 2+} located at the surface. With Pt/CeO{sub X}, a high density of defect-associated bridging OH groups react with CO to yield a high density of the formate intermediate. With Pt/MnO{sub X}, the fraction of reactive OH groups is low and much lower formate band intensities result upon CO adsorption; moreover, there is a greater fraction of OH groups that are essentially unreactive. Thus, much lower CO conversion rates are observed with Pt/MnO{sub X} during low temperature water-gas shift. As with ceria, increasing the Pt loading facilitates partial reduction of MnO{sub X} to lower temperature, indicating metal-oxide interactions should be taken into account.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- DOE - OFFICE OF SCIENCE
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1020237
- Report Number(s):
- BNL-96087-2011-JA; TRN: US201116%%217
- Journal Information:
- Catalysis Communications, Vol. 11, Issue 15; ISSN 1566-7367
- Country of Publication:
- United States
- Language:
- English
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