Surface characterization study of Au/alpha-Fe2O3 and Au/Co3O4 low-temperature CO oxidation catalysts

Au/alpha-Fe2O3 and Au/Co3O4 catalysts prepared by coprecipitation with a nominal 10 atom % Au are active for CO oxidation even at temperatures below 0 degrees 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/alpha-Fe2O3 catalyst contains more Au than that of the Au/Co3O4 catalyst. The Au is present as crystallites, and small amounts of Au(OH)(3) are also present on the Au/Co3O4 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/alpha-Fe2O3 catalyst surface. This layer is removed rapidly by ion sputtering, leaving the larger Au crystallites on the surface.