Innovative doped V/P/O catalysts for the selective oxidation of n-butane to maleic anhydride

Maleic anhydride is widely used in industry, primarily produced via the selective oxidation of n-butane using vanadium/phosphorous oxides (V/P/O) catalysts, with vanadyl pyrophosphate (VPP) as the active phase. Despite extensive research, optimizing catalyst performance remains a challenge. This study investigates the effect of new dopants on VPP-based catalysts in fluidized and fixed-bed reactors, aiming to develop superior catalysts. Supported by Polynt S.p.A., various dopant combinations were tested to enhance structure and surface properties, improving activity and selectivity. Fluidized and fixed-bed samples underwent 24-hour screening under standard reaction conditions (SOC). In fluidized reactors, dopants such as niobium (Nb), iron (Fe), cobalt (Co), molybdenum (Mo), and bismuth (Bi) were tested, but none outperformed the industrial standard (P21). While Co- and Mo-doped samples performed similarly to P21, Fe and Bi dopants resulted in poor activity due to unfavorable P/V ratios and phase composition. Fixed-bed reactors showed more promising results. Coprecipitated Fe, Co, and Bi dopants enriched catalysts with the selective δ-VOPO₄ phase. The MFC-21 catalyst (Fe+Co+Bi) surpassed the industrial standard (M-STD), achieving 71% selectivity and 82% conversion at 400°C, leading to a patent for this dopant mix. New fluidized bed catalysts incorporating Fe+Co+Bi were synthesized and compared to Nb-doped industrial precursors under newly introduced WRC conditions. Nb-doped catalysts showed high activity and selectivity, while P22 (Nb via impregnation) had lower activity but improved stability. The C22-A catalyst (Fe+Co+Bi via coprecipitation) achieved 50% yield, 66% conversion, and 77% selectivity under SOC but lost selectivity at higher temperatures. Nb impregnation (C22-I) negatively impacted surface Brønsted acidity. While fixed-bed catalysts performed best, P22 and C22-A are promising alternatives to P21, provided further improvements in activity and thermal stability.