Characterization and reactivity of sol–gel synthesized TiO2–Al2O3 supported vanadium oxide catalysts

A 90 wt% TiO2 in a titania–alumina mixed oxide support (90Ti–Al) was synthesized by the sol–gel method and characterized. Several 90Ti–Al supported vanadium oxide (vanadia) catalysts, xV90Ti–Al, were also synthesized, characterized and probed by the propane oxidative dehydrogenation (ODH) reaction. For the 90Ti–Al support and low vanadia loadings, no rutile peak was observed even after calcination at 1073 K. For vanadia loading greater than 7.5 wt%, rutile peaks were observed at 923 K and higher calcination temperatures. Characterization and reactivity studies suggest that molecularly dispersed, reducible surface vanadia species are present and active for the propane ODH reaction. However, the presence of alumina on the support surface decreased the catalytic activity relative to only titania. The activity variation with calcination temperature had a pronounced effect on the activity of some catalysts and is related to the presence/absence of the surface vanadia species and the surface Al/Ti ratio, both of which change with calcination temperature.