Preparation by atomic layer deposition and characterization of active sites in nanodispersed vanadia/titania/silica catalysts

The dispersion, acidity, reducibility and adsorption capacities of nanostructured, atomic layer deposited (ALD) V2O5/TiO2/SiO2 catalysts were examined by BET, XRD, FTIR and Raman spectroscopy, XPS, H2-TPR and microcalorimetry. TiO2-supported and standard liquid-phase impregnated catalysts were characterized for comparison, and the influence of the catalyst properties on their performance was probed in a test reaction of o-xylene selective oxidation. Gas-phase deposited, isolated vanadia species were highly dispersed independently of the support nature, whereas crystalline vanadia was detected in the impregnated catalysts with submonolayer coverage of titania. Likewise, the reducibility of the ALD catalysts was enhanced in relation to the corresponding impregnated catalysts. The activity of the ALD and impregnated catalyst increased with the decrease in number of strong surface Lewis acid and o-xylene adsorption sites. o-Xylene conversion was greater on the highly dispersed ALD catalysts on TiO2, and on TiO2/SiO2 supports with high titania content, than on their impregnated counterparts.