TAP reactor studies of the oxidizing capability of CO₂ on a Au/CeO₂ catalyst-A first step toward identifying a redox mechanism in the Reverse Water-Gas Shift reaction

As a first step toward elucidating the mechanism of the Reverse Water-Gas Shift (RWGS) reaction on a supported Au/CeO₂ catalyst, in particular the role of the redox mechanism, we have investigated the ability and activity of CO₂ for re-oxidizing a pre-reduced Au/CeO₂ catalyst surface by quantitative temporal analysis of products (TAP) measurements. It is demonstrated that a surface-reduced Au/CeO₂ catalyst can be (partially) re-oxidized by exposure to CO₂ pulses and that the surface oxygen deposited this way can be reactively removed again. The probability for oxygen deposition from CO₂, however, is significantly lower than that from O₂. Both the low reaction probability and the temperature dependence of oxygen deposition from CO₂ point to an activated step. Implications of these results for the mechanism of the RWGS reaction are discussed.