Density functional theory calculations are performed for the adsorption of O-2, coadsorption of CO, and the CO+O-2 reaction at the interfacial perimeter of nanoparticles supported by rutile TiO2(110). Both stoichiometric and reduced TiO2 surfaces are considered, with various relative arrangements of the supported Au particles with respect to the substrate vacancies. Rather stable binding configurations are found for the O-2 adsorbed either at the trough Ti atoms or leaning against the Au particles. The presence of a supported Au particle strongly stabilizes the adsorption of O-2. A sizable electronic charge transfer from the Au to the O-2 is found together with a concomitant electronic polarization of the support meaning that the substrate is mediating the charge transfer. The O-2 attains two different charge states, with either one or two surplus electrons depending on the precise O-2 adsorption site at or in front of the Au particle. From the least charged state, the O-2 can react with CO adsorbed at the edge sites of the Au particles leading to the formation of CO2 with very low (approximate to0.15 eV) energy barriers. (C) 2004 American Institute of Physics.