Atomic Structure and Special Reactivity Toward Methanol Oxidation of Vanadia Nanoclusters on TiO₂(110)

Abstract

We have grown highly controlled VO_<i>x</i> nanoclusters on rutile TiO₂(110). The combination of photoemission and photoelectron diffraction techniques based on synchrotron radiation with DFT calculations has allowed identifying these nanostructures as exotic V₄O₆ nanoclusters, which hold vanadyl groups, even if vanadium oxidation state is formally +3. Our theoretical investigation also indicates that on the surface of titania, vanadia mononuclear species, with oxidation states ranging from +2 to +4, can be strongly stabilized by aggregation into tetramers that are characterized by a charge transfer to the titania substrate and a consequent decrease of the electron density in the vanadium 3d levels. We then performed temperature programmed desorption experiments using methanol as probe molecule to understand the impact of these unusual electronic and structural properties on the chemical reactivity, obtaining that the V₄O₆ nanoclusters can selectively convert methanol to formaldehyde at an unprecedented low temperature (300 K)