Stoichiometric and reduced ceria surfaces: Atomic structure, energetics and electron localization

Abstract

We examine the (111), (110) and (100) surfaces of the stoichiometric and reduced ceria (CeO2) using density functional theory (DFT) within LSDA + U. we explore the formation mechanism of oxygen vacancy sites on CeO2 (111), (110) and (100) surfaces and their stability near the ceria surface regions. Local ordering surface defects and excess electron localization were reported. Both surface and subsurface 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 CeO2 (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 nearly the same. In the case of CeO2 (100) and (110) surfaces, Ce3+ is formed at the sites nearest to the oxygen vacancy sites. The reduced ceria expects to catalyze the dissociation of molecules on it surface. The dissociation is assisted by the oxidation of Ce3+ that generated on reduced ceria surfaces.