Ternary composite oxide catalysts CuO/Co3O4-CeO2 with wide temperature-window for the preferential oxidation of CO in H2-rich stream

A series of ternary composite oxide catalysts CuO/CO3O4-CeO2 with variable Ce/(Co + Ce) atomic ratios were prepared and employed for the preferential oxidation of CO (CO PROX). Many techniques such as N-2-sorption, XRD, H-2-TPR, O-2-TPO, CO-TPD, O-2-TPD, Cu K-edge XAFS (including EXAFS and XANES) and in situ DRIFTS were used for catalyst characterization. The catalyst CuO/CO3O4-CeO2 with Ce/(Ce + Co) ratio of 0.1 exhibits the best performance, showing not only the lowest temperature for the complete oxidation of CO (98 degrees C), but also the broadest operating temperature window for full CO conversion (98-173 degrees C). The results of N-2-sorption and temperature-programmed characterizations including H2-TPR, O-2-TPO, CO-TPD and O-2-TPD show that the CuCoCe10 catalyst possesses the highest BET surface area, the best reducibility/oxidizability and the best performance for CO and O-2 adsorption. Linear combination fitting of Cu K-edge XANES spectra reveals that multiple Cu species including Cu-0, Cu+ and Cu2+ species co-exist in the spent catalyst CuCoCe10. Stable Cu+ carbonyl species are identified as the main active reaction intermediates as revealed by in situ DRIFTS. High temperature (>120 C) can lead to the reduction of Cu+ to Cu-0, enhancing H-2 oxidation; as a result, the selectivity of O-2 towards CO2 is decreased. Based upon in situ DRIFTS results, a potential CO PROX mechanism over CuO/CO3O4-CeO2 catalysts is proposed. (C) 2013 Elsevier B.V. All rights reserved.