Within the framework of the GGA+U implementation of density functional theory, we investigate atomistic and electronic structures of Au adsorbed on the stoichiometric and the defective CeO(2){111} surfaces, in the latter of which either O or Ce vacancies are presented. We show that on the stoichiometric surface, the most stable adsorption site of Au is not on the top of the outermost O atoms, as previously suggested, but on a bridgelike site in which the Au directly binds to two O atoms. We suggest that on both sites, the original empty Ce 4f states near the Fermi level facilitate the oxidation of the Au; the preference of the Au for being on the bridgelike site is due to the larger O 2p-d(Au) mixing, accompanied by more significant electron redistributions. On the reduced surface with O vacancies, the most stable adsorption site of Au is near the vacancy position. Unlike that on the stoichiometric surface, strong ionic bonding character exists between Au and Ce, as the former becomes Au(delta-) due to the occupation of the 6s(Au) orbitals. Upon substitution for one of the Ce atoms in the lattice, the Au possesses a much stronger positive charge than that in other cases. We find that although Au is strongly bonded when it is at the Ce vacancy site, the overall binding (i.e., with the Ce vacancy formation energy being taken into account) is weaker than that for Au adsorbed at the stoichiometric surface.

The catalytic properties of Au/CeO(2) systems are sensitive to the nature of Au clusters; however, atomic information on Au clusters is sparse. In this work, we use density functional theory to investigate the nucleation of small Au clusters (up to Au(11)). By depositing Au atoms one by one at a reduced CeO(2){111} surface, we present detailed nucleation patterns. Although relatively small in size, the nanoclusters obtained exhibit interesting characteristic features. In addition to the face-centered cubic (fcc) geometry, reminiscent of bulk Au, we also find the existence of novel hexagonal close-packed (hcp) structures. Furthermore, the facets of the nanoclusters are versatile, comprising {111}/{100} combinations for the fcc-like clusters and {10(1)1}/{0001} combinations for the hcp-like. Electronically, the contact layer Au atoms that bond with surface O atoms are positively charged, which could have significant implications in catalysis.

The adsorption of water on the TiO2(110) surface has become the model process in efforts to understand metal oxide–aqueous solution interfaces. Considerable progress has been made in understanding low-coverage situations where first-principle calculations have been employed to good effect. However, current theory is less well developed for coverage above one monolayer. Here we present results of calculations on the adsorption process in forming the second water layer, that is, the adsorption of water on the fully hydrated surface. We show that there are many competitive adsorption sites owing to the numerous hydrogen-bonding possibilities. The presence of the second layer water molecules facilitates proton transfer among the adsorbates within chainlike configurations, and we present some illustration of these processes. We show how the adsorption energetics computed here along with recent calculations on defective surface and low-coverage adsorption may be used to provide a satisfactory interpretation of the temperature programmed desorption data for this system. Finally, we compute the vibrational spectrum for H and compare with the high-resolution electron-energy-loss spectroscopy measurements.