(434a) Kinetics and Reaction Mechanism for Ceria Supported Gold Water Gas Shift Catalysts
AIChE Annual Meeting
2006
2006 Annual Meeting
Catalysis and Reaction Engineering Division
Catalytic Fuel Processing
Wednesday, November 15, 2006 - 3:15pm to 3:34pm
Nanocrystalline gold catalysts are highly active for several reactions including the water gas shift (WGS)[1, 2]. The WGS is a key reaction in the production of hydrogen for a number of processes including fuel cell applications, and we have developed Au/CeO2 catalysts that are as much as four times more active than a commercial Cu-Zn-Al catalyst [2]. In general, two reaction mechanisms have been proposed for gold based WGS catalysts: the redox mechanism and the formate mechanism [3]. In this paper we discuss the WGS mechanism over a Au/CeO2 catalyst. The data were fitted to power law, Langmuir-Hinshelwood-Hougen-Watson (LHHW), and redox model based equations. The WGS orders for CO and H2O are one-half and near zeroth, respectively, for the Au/CeO2 catalyst while a commercial Cu-Zn-Al catalyst was near first order in both CO and H2O. As shown in Figure 1, the results for Au/CeO2 were best described using a LHHW model in which the reaction proceeded over two different sites with the surface reaction being rate limiting. Characterization using in-situ X-ray photoelectron spectroscopy and infrared spectroscopy also suggests that the Au/CeO2 catalyst involve formate-like intermediates. These and other results will be discussed.
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