Tunning valence state of cobalt centers in Cu/Co-CoO_1-x for significantly boosting water-gas shift reaction.

Abstract

Dual active sites with synergistic valence state regulation under oxidizing and reducing conditions are essential for catalytic reactions with step-wise mechanisms to modulate the complex adsorption sites of reactant molecules on the surfaces of heterogeneous catalysts with maximized catalytic performances, but it has been rarely explored. In this work, uniformly dispersed CuCo alloy and CoO nanosheet composite catalysts with dual active sites are constructed, which shows huge boost in activity for catalyzing water-gas shift reaction (WGSR), with a record high reaction rate reaching 204.2 μmol_CO g_cat.^-1 s^-1 at 300 °C for Cu₁Co₉O_x amongst the reported Cu-based and Co-based catalysts. A synergistic mechanism is proposed that Co^δ+ species can be easily reduced by CO adsorbed on Cu and Co⁰ can be oxidized by H₂O. Systematic in situ characterization results reveal that the addition of Cu can regulate the redox properties of Co species and thus modulate the adsorption properties of catalysts. Particularly, doping of Cu⁰ sites weakens the affinity of the surface to CO or CO₂ to a moderate level. Moreover, it also promotes the oxidation of *CO to *COOH and the desorption of the product CO₂, reducing the carbon poisoning of the catalyst and thus increasing the reactivity. The results would provide guidance for the construction of novel heterogeneous catalyst with dual active sites and clarify its underlying reactivity enhancement mechanism induced by the tunning of valence state of metal centers for heterogeneous catalytic reactions.