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

Abstract

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.