Surface science studies of the water--gas shift reaction on a model Cu(111) catalyst
The water--gas shift reaction (CO+H/sub 2/O..-->..CO/sub 2/+H/sub 2/) is a step in many industrial processes, including ammonia and hydrogen production, with potential use in coal conversion schemes as well. It is traditionally achieved on copper- or iron-based catalysts. We have studied the kinetics of this reaction at pressures of --40 Torr on a Cu(111) single-crystal surface characterized by pre- and post-reaction surface analyses (Auger electron spectroscopy, x-ray photoelectron spectroscopy, low-energy electron diffraction). Specific rates, activation energies, and reaction orders are consistent with measurements on supported Cu catalysts. The results are interpreted in terms of a mechanism whereby the reaction rate is limited by the dissociative adsorption of water. We have also characterized the sulfur poisoning of this catalyst, which appears to occur by a simple site-blocking mechanism, where the reaction ensemble size is small (less than or equal to 2 Cu atoms). Finally, we have found that Cs addition (from aqueous CsOH) enhances the reaction rate by a factor of 15. The structure of the catalyst surfaces will be discussed. After reaction, the unpromoted Cu surfaces were always completely metallic, and no surface oxygen was observable. This was true even if the Cu was heavily oxidized before reaction. With Cs addition, oxygen was always observable after reaction, and its level was roughly proportional to the Cs concentration, with an oxygen:cesium atomic ratio near unity. The mechanism of Cs promotion is discussed.
- Research Organization:
- Chemistry Department, Indiana University, Bloomington, Indiana 47405
- OSTI ID:
- 6489135
- Journal Information:
- J. Vac. Sci. Technol., A; (United States), Vol. 5:4
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CARBON DIOXIDE
CHEMICAL REACTION YIELD
CARBON MONOXIDE
CHEMICAL REACTIONS
COPPER
CATALYTIC EFFECTS
HYDROGEN
WATER
WATER GAS PROCESSES
CATALYSIS
ACTIVATION ENERGY
ADSORPTION
CHEMICAL REACTION KINETICS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
ELEMENTS
ENERGY
HYDROGEN COMPOUNDS
KINETICS
METALS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
REACTION KINETICS
SORPTION
TRANSITION ELEMENTS
YIELDS
400201* - Chemical & Physicochemical Properties