Chemically induced fast solid-state transitions of ω-VOPO4 in vanadium phosphate catalysts

Vanadium phosphates are important catalysts for the oxidation of alkanes, and commercial catalysts comprise a complex range of V4+ and V 5+ phosphates. We used three complementary in situ characterization methodologies-powder x-ray diffraction and laser Raman and electron paramagnetic resonance spectroscopies-to show that the metastable phase ω-VOPO 4 is very sensitive to many of the reactants and products of butane oxidation. A rapid transformation from ω-VOPO4 to δ-VOPO4 occurs on exposure to butane at the reaction temperature, and hence the metastable ω-VOPO4 may play a role in the formation of commercial catalysts.