Abstract: A series of V-P-Ocatalysts in the range of P/V ratio=0.9, 1.0, 1.1, with different calcination temperature and calcination atmosphere for n-butane oxidation to maleic anhydride were prepared by the method of benzyl alcohol reduction. Crystal phases of the catalysts were determined by XRD and FT-IR. The average valence of vanadium in the catalysts was determined by chemical titration. It was considered that the main factor which was related to seclectivity is the formation of crystalline catalysts, the mixed crystal of (VO)₂P₂O₇and a part of a-VOPO₄in good crystallinity is active phase in the redox dynamic process. The reaction is the reaction of structure sensitivity.

Key words: Selective oxidation of butane, V-P-O catalysts, Selectivity of maleic anhydride, Average valence of vanadium