CHARACTERIZATION OF (V2O5-WO3) ON TIOX/AL2O3 CATALYSTS BY H-1-SOLID-STATE, N-15-SOLID-STATE, AND V-51-SOLID-STATE NMR-SPECTROSCOPY

Vanadium and tungsten oxide supported on TiOx/Al2O3 catalysts have been studied by solid state NMR spectroscopy. H-1-MAS NMR spectra demonstrated that basic AlOH groups are involved in anchoring TiOx and VOx species. A certain percentage of the AlOH groups are located in positions, probably in the bulk of the alumina particles, where they remain inaccessible for interaction with titania, vanadia, or tungsten oxide. Titania modification of the Al2O3 surface leads to formation of bridging hydroxyls, namely Ti(OH)Ti and (or) Ti(OH)Al. Hydroxyl groups coordinated to Ti atoms are involved in anchoring vanadium and tungsten oxide species. VOH (and probably WOH) groups are formed when this ternary oxide phase is dispersed on the TiOx/Al2O3 support. V-51-NMR spectra indicated that tungsten oxide participates in the formation of the structure of the mixed oxide surface complexes. N-15-NMR spectroscopy of adsorbed N2O permitted the detection of strong Lewis acid sites on these multicomponent supported oxide catalysts. The acid strength of (V2O5-WO3) on TiOx/Al2O3 catalysts turned out to be comparable to that of the TiOx/Al2O3 support material. (C) 1995 Academic Press, Inc.