Abstract: In order to investigate the new reaction concerning the transformation of gas-cyclohexane into maleic anhydride and acetic acid, various solid VPO catalysts were prepared by different preparation methods. The main crystalline phase of the catalysts and the average oxidation value of vanadium in the catalysts were determined respectively by XRD、FT-IR and chemical titration. Experiment results revealed that the main crystalline phase, crystallization，activation ambience, and V4＋/ V5＋ ratio in the catalysts affected catalytic activity and selectivity. The catalysts whose main crystalline phase is (VO)2P2O7 possessed high crystallinity and feasible V4＋/ V5＋ ratio. (VO)2P2O7 calcinated in reaction ambience occupied higher selectivity.

Key words: VPO catalysts, Crystalline phase, Crystallization, Average oxidation value of vanadium, Characterization