Synthesis and Characterization of Vanadyl Hydrogen Phosphite Hydrate

Abstract

A novel method for the preparation of vanadyl hydrogen phosphite hydrates is described. The reaction of V2O5, H3PO3, and 1-propanol in the absence of water at 150 °C led to the formation of VOHPO3·1.5H2O with high surface area (ca. 50 m2/g), whereas in the presence of water VOHPO3·H2O was the unique product. The materials were characterized using a combination of techniques including elemental analysis, thermogravimetric analysis, powder X-ray diffraction, laser Raman spectroscopy, and infrared spectroscopy. On heating the sample in flowing nitrogen at 750 °C, it was found that the vanadyl(IV) hydrogen phosphite(III) hydrates transformed into vanadium(III) phosphate(V), VPO4, via an internal oxidation−reduction process between V(IV) and P(III), wherein V(IV) was reduced to V(III) and P(III) was oxidized to P(V). Whereas, heating the vanadyl hydrogen phosphite hydrates in flowing hydrogen can inhibit the phase transformation from vanadyl hydrogen phosphite to VPO4. The catalytic performance for the selective oxidation of n-butane to maleic anhydride using the final catalysts prepared by in situ activation under the reaction conditions was contrasted. It was found that the catalyst derived from the VOHPO3·H2O precursor shows a higher intrinsic activity for the production of maleic anhydride than that derived from VOHPO3·1.5H2O.