Photocatalytic Methanol Oxidation by Supported Vanadium Oxide Species: Influence of Support and Degree of Oligomerization

Supported isolated vanadium oxide (VO₄) species on silica have recently been shown to photocatalytically oxidize methanol selectively to formaldehyde. Insights into support effects and the reactivity of the different supported vanadium oxide species in photocatalytic methanol oxidation are obtained in the present study by varying the support, surface vanadium oxide loading, and synthesis procedure. Isolated and oligomeric surface vanadium oxide species supported on alumina can also photocatalytically oxidize methanol to formaldehyde. Crystalline V₂O₅ nanoparticles are inactive for photocatalytic conversion of methanol irrespective of the support, but they further convert the formaldehyde produced by the surface vanadium oxide species to surface formate species. The formation of surface formate species is also observed on the bare alumina support. Thermal catalyzed reactions take place at elevated temperatures, leading to product degradation, when attempting to desorb and quantify the photocatalysis products adsorbed on the alumina-supported samples. This study is a step forward in the directed development of active and selective sites for photocatalysis, and highlights the importance of limitation by desorption in the kinetics of photoreactions.