CHARACTERIZATION OF VARIATIONS IN VANADIUM PHOSPHATE CATALYST MICROSTRUCTURE WITH PREPARATION ROUTE

Three vanadium phosphate catalysts prepared by different methods are c ompared and contrasted for the selective oxidation of n-butane to male ic anhydride, VOHPO4 . 0.5H(2)O catalyst precursors were prepared via three distinct routes: (a) using aqueous HCl as a reductant for V2O5, (b) using isobutanol as solvent and reductant for V2O5; and (c) using isobutanol as a reducing agent for VOPO4 . 2H(2)O. The precursors were transformed under identical conditions (385 degrees C, 1.5% butane in air, 1000 h(-1), 75 h) to three activated catalysts, The morphology o f the precursors and the final catalysts have been assessed using a co mbination of X-ray diffraction (XRD), scanning electron microscopy (SE M), transmission electron microscopy (TEM), and P-31 NMR spin-echo map ping, Even though they exhibited very similar specific activities for maleic anhydride production, the three activated vanadium phosphate ca talysts were found to have widely varying morphologies, The implicatio ns of this observation are discussed and a few suggestions are made as to the possible nature of the active site in this catalyst system. Th e material derived from the reduction of VOPO4 . 2H(2)O exhibited the highest catalyst activity by virtue of its optimised (VO)(2)P2O7 morph ology and high surface area. (C) 1996 Academic Press, Inc.