Mossbauer characterisation of gold/iron oxide catalysts

Fe-57 and Au-197 Mossbauer data have been reported and discussed for a variety of catalysts of gold supported on iron oxide. The Fe-57 Mossbauer 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 Au-197 Mossbauer 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 identified by Mossbauer 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.