Raman microscopy as a tool for the surface characterization of V2O5/TiO2 catalysts before and after reaction with H2O2

Abstract

Supported vanadium oxides have been extensively used as catalysts in a variety of reactions, including selective oxidation of hydrocarbons, alkyl-aromatic and selective catalytic reduction of NO_xby NH₃. The high dispersion of vanadium in the form of a monolayer of VOx is the main reason for the better performance of the V₂O₅/TiO₂system. In the present study we have examined the surface of supported V₂O₅/TiO₂catalyst system by using Raman spectroscopy as well as the imaging technique obtained by Raman mapping; this technique is quite remarkable in following the relative intensity change of the band related to the V=O bond stretching, before and after reaction with H₂O₂. Raman mapping has been applied successfully to characterize single and mixed supported metal oxides and to investigate the structural changes of these metal oxides during reaction processes. The results have shown that V₂O₅/TiO₂catalyst can promote the oxidation reaction of organic compounds, such as methylene blue, in aqueous medium and the reaction apparently takes place via active oxidizing species, such as V=O chemical group, which are generated in the vanadium surface.