V2O5 catalysts supported on Al2O3-SiO2 mixed oxide:: 51V, 1H MAS solid-state NMR, DRIFTS and methanol oxidation studies

Alumina-silica mixed oxide, synthesized by the sol-gel technique, was used as a support for dispersing and stabilizing the active vanadia phase. The catalysts were characterized employing V-51 and H-1 solid-state MAS NMR, diffuse reflectance PT-IR, BET surface area measurements. The partial oxidation activities of the catalysts were tested using methanol oxidation as a model reaction. V-51 solid-state NMR studies on the calcined catalysts showed the peaks corresponding to the presence of both tetrahedral and distorted octahedral vanadia species at low vanadia loadings and with an increase in V2O5 content, the V-51 chemical shifts corresponding to amorphous V2O5 like phases were observed. DRIFTS studies of the catalysts indicated the vibrations corresponding tetrahedral vanadia species at low and medium loadings and at high V2O5 contents the vibrations corresponding V=O bonds of V2O5 agglomerates were observed. The V/Al-Si catalysts exhibited high selectivity for the dehydration product dimethyl ether in the methanol partial oxidation studies showing the predominance of the acidic nature of the alumina-silica support over the redox properties of the active vanadia phase. (C) 2000 Elsevier Science B.V. All rights reserved.