Effect of activation conditions on VPO catalysts for selective oxidation of C4 hydrocarbon

The catalyst precursor, VOHPO₄·0.5H₂O, was synthesized from V₂O₅ and phosphoric acid using isobutanol as reducer and activated in the atomosphere of n-butane/air and mixed C4 Hydrocarbon/air, respectively, and the products were named catalyst VPDB and VPDC and characterized by means of X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR), inductively couple plasma spectrometry (ICP), and so on. The catalytic performance of VPDB and VPDC for preparation of maleic anhydride from n-butane or mixed C₄ Hydrocarbon was investigated. The results showed that VPDB and VPDC had the same major active phase (VO)₂P₂O₇. Compared with VPDB, VPDC had higher labile lattice oxygen and lower surface area. The average V valence state of VPDB and VPDC was 4.28 and 4.12, respectively. Under the same reaction conditions, VPDC exhibted higher catalytic activity and lower selectivity for maleic anhydride. At the same reaction temperature the conversion of mixed C4 was much higher than that of n-butane, while the selectivity of maleic anhydride in oxidation of mixed C4 hydroncarbon was lower than that in oxidation of n-butane which demonstrated that the appropriate temperature of selective oxidation of mixed C4 should be lower than that of n-butane.