Boron Doping Highly Improves the Low-Temperature Reactivity of VPO Catalysts by Partially Reconstructing the Catalyst Structures

Hot spots often occur in the n-butane oxidation to maleic anhydride, and the reaction can sometimes run out of control due to the complete combustion of the n-butane or products at high temperatures, which releases a large amount of heat. To solve the hot spot problem, some promising nonmetal dopants (S, Se, Te, P, B) were investigated to enhance the low-temperature reactivity of the VPO (vanadium phosphorus oxide) catalysts, and boron was screened to be the best dopant. At a reaction temperature of 370–400 °C, the 2% B-VPO catalyst obtained MA yields of 53–58% compared to 45–53% on the undoped VPO catalyst, exhibiting superior low-temperature reactivity and operational flexibility. Besides, the 2% B-VPO catalyst also showed better reaction stability, which was essential to the nonmetal-doped catalysts. Characterization results indicated that boron doping influenced the topological transformation process from VHP (VOHPO4·0.5H2O) precursors to active VPO catalysts, forming structure disorders, lattice defects, and surface boron-containing active sites. Partial restructuring of the catalyst structure optimized the properties of both B acid and L acid and enhanced the amount of lattice oxygen and active V5+ phases. Boron doping facilitated the synergistic effect among these active sites (V5+ and V4+, B acid and L acid, Lat-O and Sur-O), further contributing to the superior catalytic performance of boron-doped VPO catalysts.