Preparation and characterisation of titania-supported vanadium-phosphorus oxide catalysts

A series of vanadium-phosphorus oxides (mainly with V:P = 1:1) supported on pigmentary anatase (10 m(2) g(-1)) has been prepared using aqueous NH4VO3 and (NH4)H2PO4 solutions, with loadings up to 11.3 wt%, equivalent to about 12.7 monolayers. Characterisation by X-ray diffraction, laser Raman spectr oscopy, X-ray photoelectron spectroscopy and temperature-programmed reducti on suggests that the main phase present at loadings below about 10 wt% is a n amorphous V-P oxide which exists chiefly as blocks of disordered material . The presence of small amounts of crystalline beta-VOPO4 and of V2O5 is in dicated at the highest loadings, especially when 1:3 and 3:1 V:P ratios are used. The two materials having the lowest loadings are active for methanol oxidation at 473-533 K, and show high selectivity to formaldehyde.