Preferential oxidation of CO in H-2 Was studied over a series of CuOx-CeO2 mixed oxide catalysts with differing Cu loadings and preparation techniques to elucidate structure and mechanism parameters required to achieve high selectivity. Using in situ diffuse reflectance infra-red Fourier transform spectroscopy (DRIFTS), CO oxidation activity is linked to Cu+ carbonyl species (similar to 2110 cm(-1)), while catalyst deactivation is associated with catalyst hydration. Active sites for both reactions are found to be reducible oxygen from highly dispersed or surface incorporated CuOx species in proximity to Ce, and are quantified utilizing anaerobic titrations. Active site concentrations (2.1-3.5 x 10(-6) Mol O* m(-2)) are correlated with surface copper content, as determined by X-ray photoelectron spectroscopy (XPS). High reaction selectivity towards CO oxidation (100% selectivity above 200 ppm CO at 333 K) is attributed to preferential adsorption of CO as well as inhibited H-2 dissociation due to oxidized copper sites. A detailed Mars and van Krevelen mechanism for CO and H-2 oxidation is proposed and supported by comparing the model to the experimental data. (C) 2009 Elsevier Inc. All rights reserved.