Effect of transition metals promoted on Vanadium phosphorus oxide (VPO) catalysts in the partial oxidation of n-pentane

Abstract

Vanadium phosphorus oxide (VPO) catalysts have been employed in partial oxidation of n-butane and n-pentane. In this study, VPO catalysts were synthesized by refluxing vanadyl phosphate dihydrate (VOPO4•2H2O) with isobutanol and modified with transition metals promoters such as Co, Bi, Fe, and Mn at the mass ratio of M/V 0.35. In the first part, Mn was found to be the best metal to improve the performances of VPO catalyst in n-pentane oxidation. Then the Mn-VPO catalysts were prepared with different ratios of Mn/V loadings at 0.25, 0.35, 0.45, 0.55, and 0.65. All the catalysts were calcined at 300ᵒC for 8 h to generate the vanadyl pyrophosphate ((VO)2P2O7) phase which is the active phase of VPO catalysts and was confirmed by the XRD results. As shown by SEM results, all the synthesized catalysts showed the rosette-shape morphologies of vanadyl pyrophosphate. The transition metal promoted catalysts presented the formation of V4+ state which provided a better catalytic performance with 42.7-55.8% n-pentane conversion, 28.9-62.5% MA selectivity, and 8-13.1% PA selectivity. The optimum ratio of Mn/V was determined to be at 0.45