Density functional theory study of water adsorption at reduced and stoichiometric ceria (111) surfaces

Abstract

We study the structure and energetics of water molecules adsorbed at ceria (111) surfaces for 0.5 and 1.0 ML coverages using density functional theory. The results of this study provide a theoretical framework for interpreting recent experimental results on the redox properties of water at ceria (111) surfaces. In particular, we have computed the structure and energetics of various absorption geometries at the stoichiometric ceria (111) surface. We find that single hydrogen bonds between the water and the oxide surface are favored in all cases. At stoichiometric surfaces, the water adsorption energy depends rather weakly on coverage. We predict that the observed coverage dependence of the water adsorption energy at stoichiometric surfaces is likely the result of dipole-dipole interactions between adsorbed water molecules. When oxygen vacancies are introduced in various surface layers, water molecules are attracted more strongly to the surface. We find that it is very slightly energetically favorable for adsorbed water to oxidized the reduced (111) surface with the evolution of H(2). In the event that water does not oxidize the surface, we predict that the effective attractive water-vacancy interaction will result in a significant enhancement of the vacancy concentration at the surface in agreement with experimental observations. Finally, we present our results in the context of recent experimental and theoretical studies of vacancy clustering at the (111) ceria surface.

Atomistic simulation of CeO2 surface hydroxylation: implications for glass polishing

“…This suggests that the (111) surface does not exhibit a strong driving force to bind hydroxide species to surface sites. These results compared favourably to the results of Kumar and Schelling [28]. In particular, we calculated a hydroxylation energy of 0.55 eV for the (111) surface at 50% hydroxylation, while Kumar and Schelling calculated adsorption energies of 0.56 and 0.58 eV for two different configurations of a 0.5 monolayer of water on the (111) surface.…”

“…Similarly, Abramowski et al [26] and Tan et al [27] simulated the hydroxylation behavior of UO 2 and PuO 2 , respectively, and again predicted that the crystallite morphology of these compounds is different in the presence of water. Finally, Kumar and Schelling recently considered the adsorption of water on the CeO 2 (111) surface via density functional theory [28]. We will compare our results to those of Kumar and Schelling in the ''Results'' section.…”

Origin of Rh and Pd agglomeration on theCeO2(111)surface

“…27͒ and other reported theoretical results. 14,28 The nonpolar CeO 2 ͑111͒ surface, the structurally most close-packed, is found to be the energetically most stable surface. Gennard et al 29 have shown that a slab containing nine CeO 2 ͑111͒ layers is sufficient to converge the important surface properties including surface energy, Mulliken charges and electron densities.…”

An experimental and DFT study of the adsorption and oxidation of NH3 on a CeO2 catalyst modified by Fe, Mn, La and Y

“…Numerous approaches based on DFT theory, ranging from LDA [20] to GGA [21] and DFT + U [8,19], have been employed to investigate cerium oxides. The LDA or GGA methods are considered unable to describe the electronic structure of CeO 2 in the presence of oxygen vacancies because of the excess electrons (4f) induced by the creation of oxygen vacancies, which can occupy the strongly localized f orbital.…”