First Principles Study of Energetics, Local Electronic States and Adsorption of H2O and H2O2 on Reduced CeO2 Surfaces*

The importance of ceria (CeO2) in catalysis originates from its remarkable redox and oxygen storage capability. It undergo repeatable Ce4$+$/Ce3$+$ redox cycles depending on the operation conditions. The great effort has been made to improve ceria reducibility. The reduction of ceria can be controlled by the oxygen vacancies. We study the energetics, local electronic states, and oxygen vacancy formation energies for the (111), (110) and (100) surfaces of stoichiometric and reduced ceria by DFT$+$U calculations. We find that ceria (111) surface is most stable, while (100) and (110) surfaces have higher formation energies. Both subsurface and surface oxygen vacancies induce the electron localization of reduced CeO2 on all these three terminations of the surface, leading to the appearance of Ce3$+$ sites. In the case of ceria (111) surface, oxygen vacancy at the surface and subsurface forms Ce3$+$ at next nearest neighbor to the vacancy. This is consistent with the experimental finding that the ratios of these two types of oxygen vacancy are almost same. In the case of ceria (100) and (110) surfaces, Ce3$+$ is formed at the sites nearest to the oxygen vacancy sites. The H2O and H2O2 adsorption and dissociation on three reduced surfaces are also investigated. Ce3$+$ generated by oxygen vacancy can promote the adsorption of H2O and H2O2.