Abstract: The effect of Ni doping (1%, 2%, and 5%) on vanadium phosphate catalysts prepared via VOPO4•2H2O was described and discussed. At low levels, the Ni dopant significantly enhanced the amount of the active lattice oxygen species O- and lowered the reduction peak temperature corresponding to the reduction of V5+and V4+phases. A combination of powderX-raydiffraction, temperature-programmed reduction, and chemical analysis data shows that at higher levels, Ni doping induced the formation of the V5+phase and suppressed the presence of the V4+phase. Previous studies have indicated that a large amount of oxygen species associated with V5+ inhibit the n-butane conversion but promote the selectivity for maleic anhydride.

Key words: vanadyl pyrophosphate, nickel, n-butane, oxidation, maleic anhydride