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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[2]       C. H. Kim and L. T. Thompson, J. Catal, 230 (2005) 66.

[3]       F. Boccuzzi, A. Chiorino, M. Manjoli, D. Andreeva, and T. Tabakova, J. Catal, 188 (1999) 176.