Quantitative measurements of CO chemisorption in the range 140-180 K, supported by FTIR data on adsorbed CO, were performed oil Au/TiO2, Au/Fe2O3, and Au/CeO2 catalysts. On the first two samples, which had similar particle size distribution, an average Au/CO chemisorption stoichiometry of about 3, referred to step-edge An atoms, Was found. On Au/CeO2, where very small clusters and quite large particles are present, the CO-chemisorbed volume was much higher than expected, due to the prevailing contribution of very small Au clusters. On the same. sample, a change in the IR absorption coefficient was observed and was reasonably explained. (c) 2005 Elsevier Inc. All rights reserved.