Dynamic Active Site Generation on CuO x /γ-Al2O3 Catalysts for CO Oxidation

Abstract

Most heterogeneous catalysts undergo dynamic changes under reaction conditions. In this study, the redox properties and dynamic behavior of CuOx/γ-Al2O3 catalysts were characterized using in situ FTIR, quasi-in situ XPS, and HS-LEIS (high-sensitivity low-energy ion scattering spectroscopy), along with XRD, H2-TPR, and CO-TPR. The topmost surface coverage of Cu species was estimated from HS-LEIS, and the oxidation states were investigated by XPS and CO-FTIR under various conditions. The results show that oxidation of the CuOx/γ-Al2O3 catalyst leads to the formation of highly dispersed Cu2+ species, which are somewhat difficult to be reduced by H2 and stable under CO oxidation conditions. A transient high activity for CO oxidation was observed for the pre-reduced catalyst. Additionally, oxidation and redispersion from Cu0 nanoparticles to highly dispersed Cu+/Cu2+ species were observed in the pre-reduced catalysts in a CO/O2/He mixture. The highly dispersed Cu+/Cu2+ species exhibited greater activity for CO oxidation and were more easily reduced by H2 than the highly dispersed Cu2+ species. The active copper species and structure–activity relationships were correlated.