A Comparative Study of Methanol Adsorption and Dissociation over WO3(001) and ReO3(001)

Abstract

Tungsten (5d46s2) and rhenium (5d56s2) form MO3 oxides (M = W or Re) with similar structures. The adsorption and dissociation of methanol on these oxide surfaces, often used to probe the surface redox centers, have been analyzed using periodic density functional calculations. Molecular adsorption of methanol at the metal site on both surfaces with 0.5 ML oxygen coverage was found to be exothermic with adsorption energies of −74 and −106 kJ/mol on WO3(001) and ReO3(001), respectively. In contrast, heterolytic dissociation of methanol to adsorbed methoxide species at the metal site and H at the surface oxygen site is not energetically favored on WO3(001) but favored on ReO3(001). The dissociation energies to form coadsorbed methoxide and hydrogen adatom are 35 kJ/mol on WO3 and −112 kJ/mol on ReO3, respectively. The activation barrier for dissociating the molecularly adsorbed methanol on ReO3(001) was determined to be 19 kJ/mol. Dehydrogenation to form coadsorbed hydroxymethyl and hydrogen adatom is not energetically favorable on both surfaces with respect to the molecularly adsorbed methanol. However, the dehydrogenation path is exothermic on ReO3 with respect to the gas phase methanol, with the heats of reaction of −25 kJ/mol, but highly endothermic on WO3, with the heats of reaction of 114 kJ/mol.