Promotion of CO and CO{sub 2} hydrogenation over Rh by metal oxides: The influence of oxide Lewis acidity and reducibility
- Lawrence Berkeley Lab., CA (United States)
An investigation has been carried out of CO and CO{sub 2} hydrogenation to methane over a Rh foil decorated with submonolayer quantities of AlO{sub x}, TiO{sub x}, VO{sub x}, FeO{sub x}, ZrO{sub x}, NbO{sub x}, TaO{sub x}, and WO{sub x}. The rate of methane formation was measured at 1 atm and the state of the working catalyst was characterized by XPS immediately after reaction. With the exception of AlO{sub x}, each of the oxides was found to enhance the rate of CO methanation relative to that observed over unpromoted Rh. The maximum degree of rate enhancement occurs at an oxide coverage of approximately half a monolayer. AlO{sub x} retards the formation of methane in direct proportion to the oxide coverage. FeO{sub x} behaves in a manner identical to that of AlO{sub x} in the case of CO{sub 2} hydrogenation, whereas all of the other oxides studied produce a maximum degree of methanation rate enhancement at an oxide coverage of half a monolayer. The enhancement of CO and CO{sub 2} hydrogenation is attributed to the formation of Lewis acid-base complexes between the oxygen and of adsorbed CO (or H{sub 2}CO formed during the reaction) and anionic vacancies present at the edge of the oxide-metal boundary. The degree of enhancement of CO and CO{sub 2} hydrogenation is found to increase with the average oxidation state of the metal in the oxide overlayer. This trend is attributed to the direct relationship between Lewis acidity of an oxide and the oxidation state of the metal in the oxide. The degree of reduction of a given oxide is found to be higher during CO{sub 2} hydrogenation than CO hydrogenation. 95 refs., 9 figs., 1 tab.
- OSTI ID:
- 113776
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 149; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
40 CHEMISTRY
ALUMINIUM OXIDES
CARBON DIOXIDE
CARBON MONOXIDE
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
HYDROGENATION
IRON OXIDES
LEWIS ACIDS
NIOBIUM OXIDES
PHOTOELECTRON SPECTROSCOPY
REDUCTION
RHODIUM
TANTALUM OXIDES
TITANIUM OXIDES
TUNGSTEN OXIDES
VANADIUM OXIDES
X-RAY SPECTROSCOPY
ZIRCONIUM OXIDES