Temperature programmed reduction (T

Temperature programmed reduction (TPR) in H2 gas suggests that several different states of CuO could be present on support CeO2, i.e., highly dispersed CuO with strong interacting with the support, well dispersed CuO clusters, and CuO crystallites [9,10,15,16]. Due to interaction of CuO with CeO2, on current reduction of CeO2 into CeO2 with CuO reductionwas often observed in TPR process of CuO/CeO2 samples, though pure CeO2 itself began to be reduced only at a much higher temperature [15,16]. During CO-PROX reaction, CuO/CeO2 catalyst may change into lower valence states, with metallic Cu formed at higher reaction temperatures [6,17,18]. This can be understood because the reaction atmosphere was reductive with presence of an excess of H2 and only a little of O2 in the feed gas, and especially O2 concentration became very low at higher reaction temperatures due to its consumption. Metallic Cu promoted hydrogen oxidation reaction and thus lowered CO oxidation conversion at the higher reaction temperatures