Role of CO2 on CO preferential oxidation over CuO/CeO2 catalyst

Abstract

The inhibiting effect of the presence of CO2 (15vol.%) in the reaction mixture of CO-PROX reaction on the performance of CuO/CeO2 catalysts has been investigated; CO2 depresses CO oxidation up to 160°C, its effect being negligible at higher temperatures. The CO2 coverage of both ceria support and catalysts has been quantitatively determined by CO2 TPD experiments and the distribution of adsorbing sites has been modeled. Two sites for CeO2 (one modified by the strong interaction between Ce and Cu when copper is added) and an additional site associated to less interacting copper for CuO/CeO2 catalysts have been identified by the mathematical model. Although ceria gives a large contribution to CO2 adsorption, the sites present in larger amount rapidly desorb CO2 in the typical temperature range of CO-PROX reaction (80–150°C), especially when copper modification induces a decrease of desorption activation energy, thus suggesting that these centres are involved in CO oxidation. Adsorption sites attributed to copper less interacting with the support still keep a fraction of adsorbed CO2 in this temperature range and the higher selectivity suggested that they can be mainly related to the H2 oxidation activity.