High temperature preparation of vanadium phosphate catalysts using water as solvent

Vanadium phosphate catalysts prepared in aqueous solution at elevated temperature ( 145 degreesC) using either H3PO3 or V2O4 as reactants are described and discussed. This methodology produces catalysts with a much higher surface area (ca. 20 m(2) g(-1)) compared with those prepared using aqueous routes using HCl as reducing agent (ca. 4 m(2) g(-1)). The materials were characterised using a combination of powder XRD, BET surface area measurement, laser Raman spectroscopy, TGA, electron microscopy and P-31 spin echo mapping NMR spectroscopy. Refluxing the precursors in water prior to activation was crucial in obtaining high surface area materials, and P-31 spin echo mapping NMR together with electron microscopy data indicate that the water reflux step influences the relative amounts of V4+ and V5+ phases present in the catalyst, as well as reducing the size of the crystallites. A correlation between the activity of the catalyst and the surface area is observed. However, a small group of catalysts display a higher activity than that expected from this correlation, and this increased activity is discussed in terms of the interaction of V4+ and V5+ phases.