Preparation of high surface area vanadium phosphate catalysts using water as solvent

The synthesis of vanadium phosphorus oxide catalysts using water as solvent is described and discussed. The use of H3PO3 as a reducing agent is contrasted with aqueous hydrochloric acid. Using H3PO3 as a reducing agent for V2O5 at 145degreesC for 72 h, together with H3PO4 or H4P2O7 as the additional phosphorus source, is found to produce VOHPO4.0.5H(2)O. Following activation in n-butane-air for 72 h, the catalysts derived from this method have surface areas (17-23 m(2) g(-1)) that are comparable to those prepared using a standard non-aqueous solvent method. The specific (mol maleic anhydride per g catalyst per h) and intrinsic (mol maleic anhydride m(-2) h(-1)) activities of the catalysts derived from using H3PO3 with water as solvent are also comparable to those for catalysts prepared using non-aqueous solvents. The activated catalysts comprise (VO)(2)P2O7, together with alpha(II)- and delta-VOPO4. Refluxing the VOHPO4.0.5H(2)O catalyst precursors in water is found to decrease the crystallite size of the precursor, and this leads to higher area activated catalysts, but does not affect the specific or intrinsic activity significantly.