Adsorption and dissociation of methanol on the fully oxidized and partially reduced (1 1 1) cerium oxide surface: Dependence on the configuration of the cerium 4f electrons

The adsorption and dissociation of methanol on the fully oxidized and partially reduced (1 1 1) cerium oxide surface is studied using the PW91 functional as well as the PW91 + U scheme. We investigate the influence of the detailed electronic structure of the Ce 4f band on the chemistry of methanol on the surface. For the partially reduced surface we obtain a spin delocalized, a ferromagnetic, and an anti-ferromagnetic solution. We find that the qualitative conclusions are independent of the spin state. Methanol adsorption is exothermic on the fully oxidized as well as on the partially reduced surface. The dissociation of methanol on the surface is enhanced by the presence of a vacancy. We localize an on-top methoxy species, where the methoxy oxygen binds to a second layer cerium atom, as a dissociation product on the fully oxidized surface. On the partially reduced surface the dissociation product is a triply bridged methoxy species, where the methoxy oxygen partly fills the oxygen vacancy in the surface. Adsorption energies are influenced by the introduction of the Hubbard (U) term. On the other hand, energy differences between surface species such as dissociation energies on the surface are less sensitive.