Insight into the Deactivation of Au/CeO2 Catalysts Studied by In Situ Spectroscopy during the CO-PROX Reaction

The activity and deactivation of Au/CeO2 catalysts in the PROX reaction were measured during long-term experiments (TOS = 160 h) by in situ DRS-UV-vis spectroscopy. During the reaction, the support showed a decrease in band gap energy. The activity and selectivity to CO2 were closely linked to the reduction of Aun+ species, the sintering of the reduced Au species, and to changes in the Ce3+/Ce4+ ratio. This ratio increased during long-term PROX experiments, showing a decrement of surface oxygen atoms from the CeO2 phase which participated in the reaction, after which the total oxygen fed to the reaction was wholly consumed. Also, almost all of the Au3+ species initially present in the catalysts were reduced to Au+ and Au. Results suggest that the activity loss is connected to the fast reduction of Au species and is also linked to changes in the redox properties of ceria, breaking the cycle that provides oxygen to the reaction. Sintering of the Au nanoparticles occurs in a longer time scale. On the other hand, in the case of fresh Au/CeO2 catalysts, the Aun+/Au-0 ratio decreased with increasing Au content. This initial ratio affects CO2 selectivity as a function of temperature.