Support Effect in Oxide Catalysis: Methanol Oxidation on Vanadia/Ceria

Density functional theory is used for periodic models of monomeric vanadia species deposited on the CeO₂(111) surface to study dissociative adsorption of methanol and its subsequent dehydrogenation to formaldehyde. Dispersion-corrected PBE+U calculations are performed and compared with HSE and B3LYP results. Dissociative adsorption of methanol at different sites on VO₂·CeO₂(111) is highly exothermic with adsorption energies of 1.8 to 1.9 eV (HSE+D). Two relevant pathways for desorption of formaldehyde are found with intrinsic barriers for the redox step of 1.0 and 1.4 eV (HSE+D). The calculated desorption temperatures (370 and 495 K) explain the peaks observed in temperature-programmed desorption experiments. Different sites of the supported catalyst system are involved in the two pathways: (i) methanol can chemisorb on the CeO₂ surface filling a so-called pseudovacancy and the H atom is transferred to an V–O–Ce interphase bond or (ii) CH₃OH may chemisorb at the V–O–Ce interphase bond and form a V–OCH₃ species from which H is transferred to the ceria surface, providing evidence for true cooperativity. In both cases, ceria is directly involved in the redox process, as two electrons are accommodated in Ce <i>f</i> states forming two Ce³⁺ ions whereas vanadium remains fully oxidized (V⁵⁺)