Elucidating the mechanism of the reverse water-gas shift reaction over Au/CeO2 catalysts using operando and transient spectroscopies

The reaction mechanism of the reverse water-gas shift reaction (rWGSR) over Au/ceria catalysts was investigated by monitoring the catalyst dynamics and reaction intermediates using operando and transient spectroscopies, as well as by DFT calculations. Combined operando Raman and UV-Vis spectroscopic analysis allows establishing a correlation between subsurface oxygen vacancies and catalytic activity. Comparison of different ceria support materials, i.e., polyhedra and polycrystalline sheets, reveals that the defect concentration is not rate-determinant. Using transient DRIFTS, we are able to identify individual steps of hydrogen dissociation on supported gold and to gain detailed insight into the reduction of CO2 via formate and carbonate formation. It is demonstrated that CO2 reduction is influenced by the surface pretreatment. Considering all spectroscopic findings, we propose an associative mechanism via carbonate and formate intermediates as the main route for the rWGSR over Au/ceria(111) catalysts, while a redox mechanism plays only a minor role.