Au/α-Fe 2 O 3 and Au/Co 3 O 4 catalysts prepared by coprecipitation with a nominal 10 atom % Au are active for CO oxidation even at temperatures below 0 °C. The surfaces of these as-prepared, powdered catalysts have been examined using X-ray photoelectron spectroscopy (XPS) and ion-scattering spectroscopy (ISS) to gain information about the composition, morphology, and chemical states of the species present at these surfaces. The nature of the Au is complex. The near-surface region of the Au/α-Fe 2 O 3 catalyst contains more Au than that of the Au/Co 3 O 4 catalyst. The Au is present as crystallites, and small amounts of Au(OH) 3 are also present on the Au/Co 3 O 4 catalyst. The ISS data indicate that a thin layer of metallic Au, which covers most of the iron oxide substrate, is present on the Au/α-Fe 2 O 3 catalyst surface. This layer is removed rapidly by ion sputtering, leaving the larger Au crystallites on the surface.
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Epling et al. (1996) studied this question.