Calorimetric measurements of the acidity of supported vanadium oxides prepared by ALE and impregnation

The surface acidic properties of supported vanadium oxide catalysts prepared by atomic layer epitaxy (ALE) and for comparison by a conventional incipient wetness impregnation were investigated by adsorption microcalorimetry, using ammonia as probe molecule. The acidic characteristics were strongly affected by the preparation method and the oxide supports. When using γ-Al2O3 and TiO2 as supports, the acidic character of supported vanadium catalysts always decreased compared to vanadia-free supports, whereas on weakly acidic SiO2, new acidic centres were created when depositing V2O5. The same types of acidic sites, Lewis and Brönsted, were present in all the catalysts, but those prepared by ALE showed stronger acidity. The ALE samples were more easily reduced by H2 thermo-programmed reduction and were twice as active as the impregnated samples in propane dehydrogenation to propene.