Density functional theory calculations corrected for on-site Coulomb interactions (DFT + U) have been performed to study supported rare earth catalysts with small Au nanoclusters (Au trimer, Au-3) adsorbed at CeO2 surfaces. The interaction of Au-3 with all the three major facets of crystalline CeO2, namely CeO2(1 1 1), (1 1 0) and (1 0 0), were systematically investigated. The results showed that Au-3 can adsorb rather strongly at the surfaces (E-ads > 3 eV), and partially reduce the CeO2 support by filling the originally empty 4f orbital of one surface Ce with an electron. Moreover, corresponding to different configurations of surface relaxation caused by Au-3 adsorption, the localized 4f electron can occur at different surface Ce near the Au-3 at each surface. By calculating adsorption of O-2, we also showed that only the surface Ce at Au-3/CeO2(1 1 0) are capable of strongly holding and activating the O-2. (c) 2010 Elsevier B.V. All rights reserved.