Mechanistic study of water–gas shift reaction over copper/zinc-oxide/alumina catalyst in a reformed gas atmosphere: Influence of hydrogen on reaction rate

Kinetic and pulse experiments were performed to elucidate the mechanism of the water–gas shift reaction (WGSR) under practical conditions. CO conversion was found to be significantly influenced by H2. The reaction was strongly suppressed at high H2 concentrations. A simple rate equation based on a competitive redox mechanism was derived. The H2O-induced oxidation of Cu0 to Cu+ was assumed to be the rate-determining step. H2 affected the CO conversion rate because it competitively reduced Cu+ to Cu0. In the proposed rate equation, the rate constant kf determines the rate of the catalytic cycle and the selectivity factor κ may control the selectivity to CO conversion. CO-pulse experiments independently yielded the selectivity factor κ (1.38), which was almost identical to that obtained from the kinetic analysis (1.39). The coincidence of these values strongly corroborates the proposed competitive redox mechanism. [Display omitted] •A competitive redox mechanism is proposed for low-temperature WGSR over Cu-ZnO-Al2O3.•The rate equation is a product of the oxidation rate and selectivity to reduction.•The detrimental effect of H2 can be explained by the competitive redox mechanism.•Results of pulse experiments support the competitive redox mechanism.•The number of active surface-Cu0 sites can be estimated from the pulse experiments.