Study of active sites and mechanism responsible for highly selective CO oxidation in H_2 rich atmospheres on a mixed Cu and Ce oxide catalyst

摘要

Preferential oxidation of CO in H_2 was studied over a series of CuO_x-CeO_2 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 (～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 CuO_x species in proximity to Ce, and are quantified utilizing anaerobic titrations. Active site concentrations (2.1-3.5 × 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.