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

•CuO/Co3O4–CeO2 [Ce/(Co + Ce) = 1/10] is more efficient for CO PROX than CuO/CeO2.•Full CO conversion and 100% selectivity of O2 to CO2 are achieved on it at 98 °C.•A very wide temperature-window (98–173 °C) for full CO conversion is observed.•CO is mainly activated and oxidized on Cu+ site by forming carbonyl intermediates.•Formation of Cu0 can enhance H2 oxidation, decreasing the O2 to CO2 selectivity.

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 N2-sorption, XRD, H2-TPR, O2-TPO, CO-TPD, O2-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 °C), but also the broadest operating temperature window for full CO conversion (98–173 °C). The results of N2-sorption and temperature-programmed characterizations including H2-TPR, O2-TPO, CO-TPD and O2-TPD show that the CuCoCe10 catalyst possesses the highest BET surface area, the best reducibility/oxidizability and the best performance for CO and O2 adsorption. Linear combination fitting of Cu K-edge XANES spectra reveals that multiple Cu species including Cu0, 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 Cu0, enhancing H2 oxidation; as a result, the selectivity of O2 towards CO2 is decreased. Based upon in situ DRIFTS results, a potential CO PROX mechanism over CuO/Co3O4–CeO2 catalysts is proposed.