Insights into the Nature of Formate Species in the Decomposition and Reaction of Methanol over Cerium Oxide Surfaces: A Combined Infrared Spectroscopy and Density Functional Theory Study

P. LUSTEMBERG; BOSCO, M.V.; A. BONIVARDI; BUSNENGO, H.F.; M.V. GANDUGLIA-PIROVANO

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Lugar: Washington; Año: 2015 vol. 119 p. 21452 - 21464

1932-7447

Formation of formate species on oxide surfacesplays a role in reactions for hydrogen production such as thewater−gas shift and the steam-reforming of alcohols. It hasbeen suggested that bridge formates are the most common andstable configuration on metal oxides. Ceria-based catalysts areimportant for these reactions where ceria is a ?non-innocent?support. In this work, the nature of the formate species that areformed during decomposition and reaction of methanol onceria surfaces have been studied using a combination ofinfrared temperature-programmed surface reaction (TPSR-IR)on a real powder catalyst support and density functional theory(DFT) together with statistical thermodynamics for modelCeO2(111) surfaces. The influence of surface oxygen vacancies, hydroxyl groups, and water has been considered. Three differentformate species have been identified (450−550 K). Initially, formates are adsorbed on the oxidized surface that is graduallyhydroxylated by the release of hydrogen from methoxy groups (>500 K), which leads to a partially reduced surface. On theformer, one kind of species is observed, whereas on the latter, the other two kinds appeared. We provide computational evidencethat the bonding is only initially of the bridge type but becomes of the monodentate type as the surface concentration of hydroxylgroups rises. The calculated frequencies of the O−C−O symmetric and asymmetric stretching modes for the three structures arein good agreement with those experimentally observed. The existence of monodentate species is discussed in terms of astabilizing effect of hydrogen bonds. The combined experimental and theoretical results on real and model systems, respectively,thus provide important insights on the reaction of methanol on ceria surfaces.