Identification of the Active Sites for CO and C 3 H 8 Total Oxidation over Nanostructured CuO−CeO 2 and Co 3 O 4 −CeO 2 Catalysts

Nanostructured Co 3 O 4 −CeO 2 and CuO−CeO 2 catalysts with the specific surface areas exceeding 100 m 2 g −1 were synthesized by a surfactant-templated method. The catalytic performance of these catalysts was investigated using the total oxidation of CO and C 3 H 8 as model reactions. The results show that the Co 3 O 4 −CeO 2 catalysts are less active for CO oxidation but are more active for C 3 H 8 oxidation as compared with the CuO-CeO 2 catalysts. Moreover, the Co 3 O 4 −CeO 2 catalysts exhibit a volcano-type performance for CO oxidation with the cobalt content increasing. The in situ diffuse reflectance infrared spectroscopy (DRIFTS) study shows that CO is adsorbed mainly as carbonyl (2106 cm −1 ) and bidentate carbonate (1568 and 1281 cm −1 ) on CuO−CeO 2, and only as bidentate carbonate (1591 and 1268 cm −1 ) on Co 3 O 4 −CeO 2 . On the basis of the results of structural characterization, redox properties, and in situ DRIFTS study, the active sites for CO and C 3 H 8 oxidation are identified, respectively. Carbon monoxide oxidation preferentially occurs at the interface between CeO 2 and CuO or Co 3 O 4, whereas propane oxidation takes place on the neighboring surface lattice oxygen sites in CuO or Co 3 O 4 crystallites. The different requirements of the active sites are determined by the different reaction mechanisms and the rate-determining steps. It is also found that the introduction of a small amount of Pd to Co 3 O 4 −CeO 2 can remarkably promote the CO oxidation activity, but it hardly enhanced the C 3 H 8 oxidation activity of the catalyst. The different reaction mechanisms, on molecular level, are identified and discussed in detail.