Cobalt and Copper Composite Oxides as Efficient Catalysts for Preferential Oxidation of CO in H2-Rich Stream

A series of Co–Cu composite oxides with different Co/Cu atomic ratios were prepared by a co-precipitation method. XRD, N2 sorption, TEM, XPS, H2-TPR, CO-TPR, CO-TPD and O2-TPD were used to characterize the structure and redox properties of the composite oxides. Only spinel structure of Co3O4 phase was confirmed for the Co–Cu composite oxides with Co/Cu ratios of 4/1 and 2/1, but the particle sizes of these composite oxides decreased evidently compared with Co3O4. These composite oxides could be reduced at lower temperatures than Co3O4 by either H2 or CO. CO and O2 adsorption amounts over the composite oxides were significantly higher than those over Co3O4. These results indicated a strong interaction between cobalt and copper species in the composite samples, possibly suggesting the formation of CuxCo3−xO4 solid solution. For the preferential oxidation of CO in a H2-rich stream, the Co–Cu composite oxides (Co/Cu = 4/1–1/1) showed distinctly higher catalytic activities than both Co3O4 and CuO, and the formation of CuxCo3−xO4 solid solution was proposed to contribute to the high catalytic activity of the composite catalysts. The Co–Cu composite oxide was found to exhibit higher catalytic activity than several other Co3O4-based binary oxides including Co–Ce, Co–Ni, Co–Fe and Co–Zn oxides.