Reaction of vanadium phosphates with alcohols at elevated temperature and pressure

Abstract

The reaction of VOPO₄·2H₂O, β-VOPO₄ and VOHPO₄·0.5H₂O with alcohols in an autoclave at elevated temperatures (100–400 °C) and pressures (1–150 bar) is described and discussed. The reduction of VOPO₄·2H₂O with alcohols at ambient pressure is a standard method of preparation for VOHPO₄·0.5H₂O which is a valuable commercial catalyst precursor for the oxidation of butane to maleic anhydride. Surprisingly, the use of higher reaction pressures presents an unexplored region, and we show that primary alcohols at high temperature and pressure reduce both VOPO₄·2H₂O and β-VOPO₄ to tetragonal VPO₄·H₂O, whereas VOHPO₄·0.5H₂O is reduced to form monoclinic VPO₄·H₂O. Previously these materials have been prepared by slow hydrothermal synthesis requiring the presence of templates, and hence we present new more facile synthetic pathways to these V(III) compounds. The catalytic performance for the selective oxidation of butane to maleic anhydride of these materials pretreated in situ with butane/air is also described and discussed in terms of the structures of the materials formed under the reaction conditions.