Preparation of Vanadium-Phosphorus Mixed Oxide (P/V=1) Catalysts and Their Application to Oxidation of Butane to Maleic Anhydride

Article abstract of DOI:10.1246/bcsj.58.2163

Several vanadium-phosphorus mixed oxides with a P/V ratio = 1 have been prepared and the relationships between the structure of catalyst and the catalytic function for the selective oxidation of butane to maleic anhydride were examined.As revealed from XRD, IR, XPS, and redox titration studies, five among them were presumably composed of crystalline single phases, that is, α-VOPO4, β-VOPO4, and (VO)2P2O7 as well as unknown phases X₁ and X₂.The valences of vanadium of these catalysts were close to five, except for (VO)2P2O7 (the valence was four).These phases were prepared, respectively, by controlling the kind of precursors and the calcination conditions.The selectivity to maleic anhydride differed markedly among these catalysts, although the rate did not change much when it was normalized to surface area.The selectivity at 440 deg C was less than 20percent for α- and β-VOPO4, 40percent for X₁ and X₂, and 70percent for (VO)2P2O7.Amorphous phases having V(4+) were much less selective than (VO)2P2O7.No structural changes of the catalysts after use were observed in the case of α-, β-VOPO4, and (VO)2P2O7.Therefore, the effective phase for selective oxidation of butane to maleic anhydride was speculated to be a phase like (VO)2P2O7 in which the valence of vanadium is four and the structure is stable under the reaction conditions.