Theoretical studies of the adsorption of CO and C on Ni(111) and Ni/CeO2(111): Evidence of a strong metal-support interaction

The catalytic CO methanation reaction on Ni/CeO2(111) systems is known to depend on Ni coverage: at medium and large coverages, Ni/CeO 2(111) surfaces are able to catalyze methane production, whereas at small coverage they become efficient catalysts for the water-gas shift reaction. Electronic structure, geometries, and the adsorption of C and CO on small Nin (n = 1 and 4) particles deposited on CeO2(111) have been studied using density functional theory (DFT) with the DFT+U approach and compared with Ni(111) and CeO2(111). The most stable Ni4 cluster has a pyramidal structure (pyr-Ni4), and a planar rhombohedral structure (r-Ni4) is less stable by ∼0.2 eV. Metallic Ni particles are partially oxidized (Ni2+/Ni1+) upon deposition on the ceria support, which is partially reduced. C species are strongly bound on Ni(111), whereas on Ni/CeO2(111), and on the bare support, oxidative adsorption (C + CeO2 → CO + CeO 2-x) is mostly preferred, opening a Mars-van Krevelen mechanism to prevent coke formation. The exothermicity of nonoxidative adsorption of C on nickel sites follows the trend: Ni1/CeO2(111) < pyr-Ni4/CeO2(111) < Ni(111). On these systems, CO adsorption is nonoxidative. The C-O bond strength follows the inverse trend of the nonoxidative adsorption of C: Ni(111) < pyr-Ni4/CeO 2(111) < Ni1/CeO2(111). The stronger C-O bond found for the CO/Ni1/CeO2(111) system compared with CO/Ni(111) provides an explanation of the Ni coverage dependence reported for the CO methanation reaction on Ni/CeO2(111) catalysts. The strong electronic perturbations in the Ni1 adatoms produce a drastic change in their chemical properties. © 2013 American Chemical Society.The authors acknowledge Miguel Vicente, Jesús Mingorance, and Germán Rivas for useful discussions and the following sources of funding: COMBACT S-BIO-0260/2006 (Comunidad de Madrid to M.V.), NOBIMAT-M S2OO9/MAT·1507 (Comunidad de Madrid to M.V.), DIVINOCELL FP7 HEALTH-F3-2009-223431 (European Commission to M.V.), Plan Nacional BIO2008-04478-C03-00 (Ministerio de Ciencia e Innovación, Madrid, Spain, to M.V.), and CONSOLIDER INGENIO 2010 CSD2007-00010 (Ministerio de Ciencia e Innovación to M.V.). A.V.K. was supported by a fellowship from the Spanish Government (Ref SB97-BL 0332192), M.K. was a Ph.D. fellow of the La Caixa Foundation International Fellowship Programme (La Caixa/CNB), and S.C. acknowledges Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain, for JAE-intro grants.Peer Reviewe