Photoreaction Study of Methanol Adsorption Complexes on VO₂(V₂O₅)_<i>n</i>⁺ (<i>n</i> = 1–3) Clusters at 355 nm

Abstract

VO₂(V₂O₅)_<i>n</i>CH₃OH⁺ (<i>n</i> = 1–3) complexes are generated from the interactions of pregenerated VO₂(V₂O₅)_<i>n</i>⁺ clusters with CH₃OH in a fast flow reactor. The photoreactions of these three adsorption complexes at 355 nm are characterized by a high-resolution tandem time-of-flight mass spectrometer. The major photoproducts of V₃O₇CH₃OH⁺ are CH₂O and V₃O₇H₂⁺, whereas those of V₅O₁₂CH₃OH⁺ and V₇O₁₇CH₃OH⁺ are CH₃OH and the corresponding V_<i>x</i>O_<i>y</i>⁺ (<i>x</i>,<i> y</i> = 5,12 and 7,17). Collision-induced dissociation and density functional theory/RRKM calculations suggest that CH₃OH is dissociatively adsorbed on V₃O₇⁺, whereas it is nondissociatively adsorbed on V₅O₁₂⁺ and V₇O₁₇⁺. This study suggests that the thermal dissociation of CH₃OH to CH₃O is the prerequisite for its photo-oxidation into CH₂O, which may shed light on the photochemistry of methanol over transition metal oxide surfaces