A DFT+U revisit of reconstructed CeO2(100) surfaces: structures, thermostabilities and reactivities

Abstract

Cerium dioxide (CeO₂) shows wide catalytic applications by virtue of its excellent oxygen storage capacity. The CeO₂(100) surface has aroused particular interest because of its intrinsic polarity; however, it suffers from structural reconstruction, which consequently hinders experimental and theoretical studies. In this work, we performed density functional theory calculations with on-site Coulomb interaction correction to investigate and further correlate the geometric and catalytic properties of reconstructed CeO₂(100) surfaces. By introducing CeO₂ units on a previous O-terminal model, the surface exposed CeO₄ pyramids with gradual increase in coverage and eventually transformed into a Ce-terminal structure. The corresponding thermostabilities were evaluated by calculating the surface energy and oxygen vacancy formation energy. We also showed that the CO oxidation on the reconstructed CeO₂(100) surfaces favored the Mars–van-Krevelen mechanism. The most stable CeO₄-terminal type of reconstruction, covered with a half overlayer of CeO₄ pyramids on the surface, was capable of directly producing CO₂ without forming bent CO₂ intermediates and carbonate byproducts. Moreover, coordinatively unsaturated Ce ions at the pyramid apex provided extra accommodation to the reacting CO, thus lowering the reaction barrier of the key C⋯O coupling step relative to that of the O-terminal surface. We finally generalized a unified picture of the dynamic changes in the thermostability and catalytic activity along with the structural reconstruction of the CeO₂(100) surface. The CeO₄-terminal type of reconstruction was theoretically predicted to be highly efficient for catalyzing CO oxidation.