Raman spectroscopic study of titania-supported vanadia catalysts

Abstract

Raman spectra are reported of four catalysts containing different vanadia loadings and prepared by calcination of anatase impregnated with ammonium metavanadate from an aqueous solution of oxalic acid. The spectra of vanadia components at loadings higher than that required for theoretical monolayer coverage of the anatase support surface resembled the spectrum of vanadium(V) oxide. Different spectra for loadings less than that for monolayer coverage are interpreted in terms of a bonded vanadia layer in which each exposed vanadium ion is coordinatively unsaturated after high-temperature thermal treatment. Adsorption of H₂O, which is shown to be reversible, leads to a weakening of the V—O bond.