Reactivity on the (110) Surface of Ceria: A GGA+<i>U</i>Study of Surface Reduction and the Adsorption of CO and NO₂

Abstract

The geometries and electronic structures resulting from surface reduction, CO adsorption, and NO 2 adsorption at the (110) surface of CeO 2 have been calculated using density functional theory corrected for on-site Coulomb interactions, GGA+ U . We report a novel electronic structure for the reduced surface, denoted the split vacancy, which is more stable than the previously reported simple vacancy with subsurface Ce III . Analysis of CO adsorption modes highlights the importance of the geometry of the CO molecule when in contact with the surface, with a tilted adsorption mode being most energetically favorable with the formation of a carbonate anion coupled with surface reduction. A new bidentate adsorption mode is observed for NO 2 adsorption, accompanied by partial surface oxidation. These novel structures observed on reduction, CO adsorption, and NO 2 adsorption are all energetically more stable than the previously reported structures. In all of the systems, it was found that the location of the Ce III ions did not have a strong effect on the energetics, although they were coupled to strong local distortions of the structure.