Capping experiments reveal multiple surface active sites in CeO2 and their cooperative catalysis†
Understanding of surface active sites (SAS) of CeO2 is crucial to its catalytic applications. In the present study, we have employed capping experiments, DFT calculations, and spectroscopic characterization to study pristine CeO2 catalyst. We find that multiple SAS coexist on the CeO2 surface: oxygen vacancies as redox sites and the coordinately unsaturated Ce cations near the oxygen vacancies and the neighboring oxygen ions as Lewis acid–base sites. Dimethylsulfoxide (DMSO), pyridine, and benzoic acid are utilized to cap the redox sites, Lewis acid sites, and base sites, respectively. Selective capping on the redox site does not have much effect on the acid–base catalysis, and vice versa, indicating the distinct surface proximity and independent catalysis of these SAS. We draw attention to a relationship between the well-known redox sites and the surface Lewis acid and Lewis base pairs on CeO2 surface, which are responsible for driving various heterogeneous catalytic reactions.