Role of regulating synthetic solvents in enhancing the catalytic performance of VPO catalysts for n-butane oxidation to maleic anhydride

Abstract

Vanadium phosphorus oxide (VPO) catalysts have been successfully applied in the selective oxidation of n-butane to maleic anhydride (MA). However, there is still much work to be done to enhance the n-butane conversion while maintaining a relatively high MA selectivity. Regulating the solvents in preparing VPO catalysts is an effective way to improve the catalytic performance. In this work, the correlation between the physicochemical properties of VPO catalysts and the composition of solvents was investigated by combining various characterization techniques to reveal the role of regulating synthetic solvents in enhancing the catalytic performance. Varying synthetic solvents could regulate both the synthetic mechanism and crystal growth of VOHPO4·0.5H2O. The VOHPO4·0.5H2O tended to form a nice plate-like structure in isobutanol but possessed large crystallite sizes and a low specific surface area. The introduction of n-butanol prevented the continuous growth of VOHPO4·0.5H2O, reducing the crystallite sizes and thus increasing the specific surface area. Introducing the n-butanol also optimized the catalyst surface chemical properties. The best catalyst synthesized in a solvent containing 80 % n-butanol and 20 % isobutanol enhanced the n-butane conversion from 71 % to 87 % while maintaining the MA selectivity (64 %) almost unchanged compared to the catalyst synthesized in a conventional solvent.