Exafs study of the decomposition products of ethanol-pillared vanadyl (IV) phosphate

The optimal catalyst for the oxidation of butane to maleic anhydride is believed to by ?-(VO)2P2O71 formed by thermal treatment of VOHPO4 0.5H2O at ca. 400°C2. The mechanism is topotactic, the change from face -shared to edge shared VOO5 octahedra requiring no breaking of V-O-P bonds2. The last-mentioned is prepared from V2O5 and excess H3PO4 in EtOH2. A further product is obtainable from this reaction, (VOHPO4)2 2.5H2O EtOH, also a layered material but with an enlarged interlayer distance of 13.48 Å3 This "ethanol-pillared" material gives a calcination behaviour different than that of VOHP4 0.5H2O. The XAS spectra of the freshly calcined products obtained along the TG curve (at 110, 230, 400, and 700° C) have been measured and analysed to cast further light on the topotacticity of precursors to V-O-P catalysts. Calcination at 700° C (Pt crucible) gave two distinct phases, one yellow and the other green; they were separated mechanically. © 1989.