Preparation of VPO Catalysts and Effect of Zirconium Promoter on the Selective Oxidation of Pentane

This study focuses on the effects of reducing solvents used in the preparation of vanadyl pyrophosphate (VPO), and ZrO2 and (ZrO)2P2O7 promoters on the structure and catalytic performance of VPO catalysts. The VPO catalysts were prepared by the following steps: 1) Formation of vanadium phosphate by the reaction of V2O5 and H3PO4, 2) Synthesis of VPO precursor through the reduction of vanadium phosphate by reducing solvents, and 3) Activation of the precursor. For Zr promoted VPO, Zr was added to the precursor before activation. The P/V atomic ratios of different VPO catalysts, which were prepared by using different reducing solvents, were different. The precursor prepared by using isobutanol or isobutanol-benzyl alcohol contained VO(H2PO4)2 and VOHPO4?0.5H2O. The precursor prepared by using hexanol also contained VO(H2PO4)2 and VOHPO4?0.5H2O crystal phases, but the amount of VOHPO4?0.5H2O was much less than that of VO(H2PO4)2. After activation, all the VPO catalysts, prepared by using different reducing solvents, contained only the (VO)2P2O7 crystal phase. The VPO prepared by using isobutanol-petroleum ether as reducing solvent was the most active, while the VPO prepared by using hexanol had the lowest activity. Nevertheless, their total selectivity to phthalic and maleic anhydrides was almost the same. Both ZrO2 and (ZrO)2P2O7 promoters increased the activity and selectivity of VPO, but ZrO2 promoter increased the activity of VPO more drastically than (ZrO)2P2O7 promoter.