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 Au⁰. 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⁺/Au⁰ ratio decreased with increasing Au content. This initial ratio affects CO₂ selectivity as a function of temperature.