Synthesis of vanadium phosphorus oxide catalysts promoted by iron-based ionic liquids and their catalytic performance in selective oxidation of n-butane

A series of vanadium phosphorus oxide (VPO) catalysts have been firstly synthesized using iron-based ionic liquids (ILs) as additives for selective oxidation of n-butane to maleic anhydride (MA) in this work. Meanwhile, VPO catalysts doped with inorganic iron salts were also prepared for comparison. The catalytic evaluation presented that iron-based IL modification remarkably enhanced the n-butane conversion and MA yield. A combination of techniques including XRD, Raman, TG, BET, SEM, TEM, XPS and H-2-TPR was employed to investigate the intrinsic distinction among these catalysts. The results demonstrated that iron-based ILs notably change the morphology of the VPO catalyst from a plate-like structure into chrysanthemum-shape clusters, leading to a significant increase in the surface area of the catalyst, and largely promote the formation of (VO)(2)P2O7. All of these were closely associated with the synergistic effect existing between the structure-oriented cations and metal anions in ILs during the preparation of the VPO catalyst. In addition, the differences in the structure and redox properties of the catalysts studied were also discussed and compared with those doped with conventional inorganic salt additives