The preparation of vanadium phosphorus oxide catalysts for the oxidation on n butane to maleic anhydride is discussed. In particular the preparation route based on the reduction of VOPO4 . 2H(2)O with alcohols is described in detail and contrasted with two other preparation methods : (i) using aqueous HCl as a reductant for V2O5 and (ii) using isobutanol as reductant and solvent for V2O5. The catalytic performance of final catalysts prepared by in situ transformation under the reaction conditions is contrasted. It is found that catalysts derived from the reduction of VOPO4 . 2H(2)O with 1-alcohols tend to give high activity catalysts by virtue of the high surface area material (typically 40 m(2) g(-1)) generated by this synthetic method. The preparation of VO(H2PO4)(2) by two routes is also described and it is shown that when this material is used as a catalyst precursor, final catalysts are ultra-selective for formation of maleic anhydride, together with furan. The characterisation of all these catalysts using various electron microscopy techniques is described and the morphology of the active catalysts is discussed.