The acid-base character of vanadium pentoxide, V2O5/SiO2 and V2O5/γ-Al2O3 catalysts has been investigated by adsorption of ammonia and sulphur dioxide using microcalorimetry. By depositing vanadium
oxide on silica; new surface sites are formed which present more acid strength than bulk vanadium pentoxide and pure silica.
Alumina-supported vanadium catalysts can be regarded as acidic monolayers VOx. Sulphur dioxide was found to be selective for uncovered alumina.