Maleic anhydride (MA) is a kind of important organic chemical raw materials and fine chemical products, has a wide application and strong market demand, while vanadium phosphorus oxide (VPO) catalyst is the most effective catalyst for n-butane selective oxidation to maleic anhydride. However, the catalysts suffer from the shorts of low activity, selectivity. Many efforts had been devoted to improve their catalytic performance. Among them, modification with metal promoters was considered as an effective method. In the present work, Ti/Zr promoter was selected as additive to modify VPO during its preparation with organic medium method. Their catalytic performance for selective oxidation of n-butane to produce maleic anhydride were tested in fixed-bed reactor at 420℃ with gas hourly space velocity of 2000 h?1. The effects of metal element, precursor and additive amount of promoters on the catalytic performance were investigated in details. The change of phase structure, the morphology as well as electronic properties of catalysts were characterized by X-ray diffraction, Raman, SEM, XPS. Compared with VPO catalyst without promoter, the VPO catalysts modified with Ti/Zr promoter effectively improved the catalytic performance for n-butane conversion rate and maleic anhydride selectivity. Especially, for the VPO catalyst promoted by Zr(NO3)4 doping with molar ratio of Zr to V of 1.5%, the conversion rate of n-butane can reached 99.1% and the yield to maleic anhydride was 54.4%. The promoters did not change the phase structure of the catalyst, but promoted the formation of the active phase (VO)2P2O7 and change the morphology of the catalyst, forming smaller size of VPO sheet and correspondingly exposing more active sites, furthermore, the interaction between the promoters and V has great effects on the concentration of P and the valence of V on the surface of VPO catalyst. In addition, the chemical compound formation of promoter elements had an important influence on the performance of VPO catalyst. When Zr(NO3)4 was used as the promoter, the conversion of n-butane was much higher than that with the promoter of ZrO2. Further, the promoter elements also had important influence on the performance of VPO catalyst. Compared with ZrO2, the catalysts modified by TiO2 showed better catalytic performance because Ti can better enter the lattice of catalyst instead of V.
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