Selective CO oxidation in rich hydrogen over CuO/samaria-doped ceria

Abstract

The selective oxidation of CO in a H 2-rich environment was studied over copper oxide supported on samaria-doped ceria (SDC). Activity tests, as well as H 2- and CO-temperature programmed reduction (CO-TPR), were carried out to seek insight into the effects of metal/support interaction occurring in the reaction. The interfacial active centers at the metal/support interfaces are inferred to be the major active sites of the reaction. By comparing the selective CO oxidation in Ar and in an atmosphere rich in H 2, we found that the conversion of CO was inhibited by H 2 at temperatures higher than 90 °C. In the H 2-rich atmosphere, the oxidation of CO and H 2 picked up considerably at 80 and 130 °C, respectively, due to differences in the reactivity of CO and hydrogen toward interfacial oxygen ions. Once bulk copper oxide is reduced by CO or H 2, the metastable states formed on the surface of the bulk CuO may serve as active sites, in addition to interfacial active centers, for the selective CO oxidation in excess H 2. CO has higher reactivity toward interfacial oxygen ions. Besides the interfacial active centers, the metastable copper clusters may also contribute to the occurrence of hysteresis in H 2 oxidation. Selectivity of the CuO/SDC catalyst results mainly from differences in the reactivity of CO and H 2 with these oxygen ions. By preparing SDC supports and CuO/SDC catalysts with different surface areas and dispersions, it was found that, although the better-dispersed catalysts exhibited higher CO conversions, more pronounced hydrogen oxidation was observed with these catalysts, thereby resulting in severer decline in selectivity.