Evolution of active species of nanostructured anatase-supported V–O–Mo catalyst in the course of reduction and oxidation

A nanostructured anatase supported V–O–Mo catalyst with V:Mo:Ti=1:9:90, obtained by sol–gel method from inorganic substrates, was investigated. The structure of the species formed on the catalyst surface in the course of synthesis was determined and its evolution during oxidation and reduction was studied by the FT Raman spectroscopy. Vanadia-like monolayer islands with some molybdenum atoms substituted for vanadium ones were found to prevail on the surface of the catalyst. Oxidation was revealed to cause monolayer islands to join through monolayer bridges formed by vanadium segregating on the surface. However, reduction of the oxidised catalyst was shown to result in the splitting of the monolayer islands into smaller ones with higher molybdenum content. During the strong reduction irreversible transformation of the vanadia-like surface species into the resembling molybdena ones was observed.