Carrier Effect on the Nature of V4+ and Active Oxygen Species in Vapor-phase Oxidation of Butadiene over Supported Divanadium Pentaoxide Catalysts

Abstract

Abstract The reactivity of V4+ with gaseous oxygen formed on various kinds of supported V2O5 catalysts has been investigated by ESR. The results are discussed as carrier effect in relation to the selectivity for maleic anhydride formation during the course of the vapor-phase oxidation of butadiene. V4+ formed on Al2O3 (V/Al≤10/90 atom ratio) and MgO (V/Mg≤30/70) showed a hyperfine ESR structure and was hardly oxidized whereas V4+ formed on SiO2 (V/Si≥5/95) had the singlet ESR signal and was easily oxidized. Formation of these two kinds of V4+ was observed on V2O5–Al2O3 (V/Al≥20/80). They were similarly observed in the case of V2O5-TiO2, but some portion of V4+ having the hyperfine structure was also oxidized. The selectivity was high over the catalysts forming the reactive V4+ as compared with those forming the unreactive one. The reactive V4+ was shown by X-ray diffraction to be preferentially formed in crystalline V2O5. Study of the reduction and reoxidation of unsupported crystalline V2O5 by means of IR and the effect of addition of alkali metal oxide on the catalytic activity of the supported V2O5 were discussed. The important role of double bond type lattice oxygen V=O in maleic anhydride formation was proposed.