ON THE ROLE OF THE VO(H2PO4)(2) PRECURSOR FOR N-BUTANE OXIDATION INTOMALEIC-ANHYDRIDE

The catalytic role of VO(H2PO4)(2), the precursor of the VO(PO3)(2) ph ase, has been studied for n-butane oxidation to maleic anhydride. By c omparison with the activated VPO catalyst, derived from the VOHPO4 . 0 .5H(2)O precursor phase, VO(H2PO4)(2) gives a highly selective final c atalyst. The total oxidation products CO and CO2 are not observed unde r any of the conditions examined, a result confirmed by extensive cata lyst testing and carbon mass balances. The final catalyst derived from VO(H2PO4)(2) has a low surface area, ca. 1 m(2)/g, and consequently d emonstrates low specific activity on the basis of n-butane conversion per unit mass. However, the intrinsic activity (activity per unit surf ace area) is found to be higher than that for catalysts derived from V OHPO4 . 0.5H(2)O. Since some VO(H2PO4)(2) is present in VOHPO4 . 0.5H( 2)O, which is the precursor of the industrial catalyst, the results of this study complicate the simple model in which the (VO)(2)P2O7 phase derived from VOHPO4 . 0.5H(2)O is responsible for the selective oxida tion 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 o xidation catalysts. (C) 1995 Academic Press, Inc.