Transient analysis of the reverse water gas shift reaction on Cu/ZrO2 and Ga2O3/Cu/ZrO2 catalysts

The performance of two copper-based catalysts, Cu/ZrO2 and Ga2O3/Cu/ZrO2, in regards the reverse water gas shift (RWGS) reaction as compared with their reaction rates for the methanol synthesis reaction (R-CH3OH) was studied using H-2/CO2 mixtures at 1.6 and 0.1 MPa, at 498 K. The reactivity studies were carried out using a Carberry-type microcatalytic reactor operated in the batch (transient) mode after H-2 prereduction at 523 K (2 h). Measurements of the catalytic activity were also made using D-2/CO2 mixtures (0.1 MPa, 498 K) to assess isotope effects. For Cu/ZrO2, the initial RWGS reaction rate using D-2 instead of H-2 was slightly higher whereas such rate was about equal for the ternary catalyst. Kinetic rate expressions obtained from the Langmuir-Hinshelwood-Hougen-Watson formalism were used to model and analyze the experimental results and the reaction mechanism(s) of the RWGS on these catalysts. Congruence was found between the experimental results and a reaction mechanism where (predominantly) CO2 adsorbs dissociatively on the Cu particles (rate-determining step). The reduction of (ad) oxygen and surface hydroxyls follow afterwards.