ELECTRON-MICROSCOPY STUDIES OF VANADIUM PHOSPHORUS OXIDE CATALYSTS DERIVED FROM VOPO4-CENTER-DOT-2H(2)O

An electron microscopy study of vanadium phosphorus oxide (VPO) cataly sts is reported. The catalyst precursor VOHPO4 . 0.5H(2)O was prepared from VOPO4 . 2H(2)O using isobutanol as the reducing agent. The catal yst was then fully activated by heating for ca. 75 h under reaction co nditions (385 degrees, GHSV 1000 h(-1), 1.5% butane in air), Scanning electron microscopy studies demonstrated that a topotactic transformat ion occurs between the precursor and the final catalyst. Transmission electron microscopy experiments revealed that there were three distinc tive morphologies present in the final catalyst; namely (i) rosette sh aped clusters composed of (VO)(2)P2O7 crystallites, (ii) crystalline p latelets of alpha(I)I-VOPO4 and (iii) disordered platelets exhibiting surface patches of(VO)(2)P2O7. This latter morphology corresponds to t he disordered remnants of hemihydrate particles which have only partia lly transformed to (VO)(2)P2O7. The (VO)(2)P2O7 platelets were found t o be the majority phase making up more than 95% of the volume fraction .