Chemically Induced Fast Solid-State Transitions of$\omega-VOPO_4$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$\omega-VOPO_4$is very sensitive to many of the reactants and products of butane oxidation. A rapid transformation from$\omega-VOPO_4$to$\delta-VOPO_4$occurs on exposure to butane at the reaction temperature, and hence the metastable$\omega-VOPO_4$may play a role in the formation of commercial catalysts.