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Gold catalysts supported on iron oxide have been characterized by X-ray photoelectron spectroscopy (XPS). Depending on the method of preparation and pretreatment, di †erent gold species have been detected on the catalyst surface. In the absence of thermal treatment, the XPS spectra of the impregnated samples show the formation of gold(III) (oxy)chloride species. No metallic gold is formed. Both metallic and oxidized gold species are instead present on the surface of the samples prepared by coprecipitation. Oxidized gold(III) species are predominant on the uncalcinated catalysts. After treatment at high temperature and/or under reaction conditions the amount of metallic gold increases. The XPS data have been correlated with the activity of the investigated catalysts in the oxidation of carbon monoxide at low temperature.

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57Fe and 197Au Mo ssbauer data have been reported and discussed for a variety of catalysts of gold supported on iron oxide. The 57Fe Mo ssbauer spectra show that iron is present as ferrihydrite, haematite and goethite in amounts that depend on the conditions of preparation. The highest amount of ferrihydrite is observed in the samples prepared by coprecipitation. The 197Au Mo ssbauer spectra reveal the formation of two main gold species, i.e., metallic gold and oxidic trivalent gold. The presence of gold favours the formation of ferrihydrite over that of haematite. No direct correlation was found between catalytic activity towards CO oxidation and the Au species identiÐed by Mo ssbauer spectroscopy, but catalyst activity was found to increase with the relative amount of ferrihydrite. It is suggested that the ferrihydrite is important for activation of molecular oxygen.

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