Advances in research of nanomaterials have brought up new opportunities for tailoring and control of catalysts in heterogeneous catalysis.In this work,CO oxidation reactions over defect surfaces of ceria (CeO2) have been investigated by using periodic density functional theory (DFT) with a slab surface model.We have calculated the diffusion properties for single oxygen vacancy and oxygen-vacancy clusters and the catalytic cycle of CO oxidation at the defect sites over CeO2 (011) and (111) surfaces.It is shown that the catalytic activity directly correlates with the stability of the surface vacancy,which is in principle determined by the localization of the electrons.The present results indicate that the reactivity of different surfaces can be predicted through computational modeling,which can help to designing new catalysts with well-defined reactive sites.