On the Role of the VO(H2PO4)2 Precursor for n-Butane Oxidation into Maleic Anhydride

Article abstract of DOI:10.1006/jcat.1995.1167

The catalytic role of VO(H2PO4)2, the precursor of the V O(PO3)2 phase, has been studied for n-butane oxidation to maleic anhydride.By comparison with the activated VPO catalyst, derived from the VOHPO4*0.5H2O precursor phase, VO(H2PO4)2 gives a highly selective final catalyst.The total oxidation products CO and CO2 are not observed under any of the conditions examined, a result confirmed by extensive catalyst testing and carbon mass balances.The final catalyst derived from VO(H2PO4)2 has a low surface area, ca. 1 m²/g, and consequently demonstrates low specific activity on the basis of n-butane conversion per unit mass.However, the interinsic activity (activity per unit surface area) is found to be higher than that for catalysts derived from VOHPO4 * 0.5H2O.Since some VO(H2PO4)2 is present in VOHPO4 * 0.5H2O, which is the precursor of the industrial catalyst, the results of this study complicate the simple model in which the (VO)2P2O7 phase derived from VOHPO4 * 0.5H2O is responsible for the selective oxidation of n-butane.The observation that the precursor VO(H2PO4)2 can generate catalysts of high specific activity and of total selectivity to partial oxidation products might provide a useful insight into the design of a new series of high activity and high selectivity partial oxidation catalysts.