Identification of the Active Sites for Low Temperature CO Oxidation over Nanocrystalline Co3O4 Catalysts

The microstructural properties of dry-grinding derived Co3O4 catalysts pretreated under different atmospheres, in relation to the activities on CO oxidation were investigated. The Co3O4 synthesized by soft reactive grinding and pretreated with O-2 resulted in the best activity, with 100% conversion of CO at -52 degrees C, superior to that of Co3O4 pretreated with He. To find out the active sites on Co3O4 for low temperature CO oxidation, the characterizations of the cobalt oxides had been investigated by means of N-2 physisorption, XRD, TEM, H-2-TPR, CO-titration, XPS and O-2-TPD technologies. XPS of Co2p results show that it is difficult to ascribe the difference in catalytic performance to the surface concentration of active Co3+ sites. A correlation between the activity and the CO-titration and O-2-TPD results for Co3O4 reveals that a high abundance of readily accessible superficial electrophilic oxygen (O-) species is important for achieving a high activity. Therefore, CO oxidation takes place on the surface active oxygen sites in Co3O4 crystallites via the suprafacial mechanism.