A Theoretical Study of Methanol Oxidation Catalyzed by Isolated Vanadia Clusters Supported on the (101) Surface of Anatase

A theoretical model has been developed for describing isolated vanadate species dispersed on the (101) surface of anatase that takes into account the equilibration of the supported species with gas-phase oxygen. The lowest energy of the combined solid and gas phases identifies the VOx species with the optimal structure and composition. This model of VOx species supported on the surface of anatase is then used to analyze the reaction path for methanol oxidation to formaldehyde. The chemisorption of methanol is found to proceed preferentially by addition across a V–O–Ti bond to form V–OCH3 and Ti–OH species. The rate-limiting step for the formation of formaldehyde takes place via the transfer of a hydrogen atom from V–OCH3 bound to an oxygen atom bridging two Ti atoms, i.e., a Ti–O–Ti group located adjacent to the supported vanadate species. This step is found to have the lowest apparent activation energy of all pathways explored for the formation of formaldehyde.