The surface acidic properties of sulfated vanadia–titania catalysts prepared by various methods were investigated by adsorption
microcalorimetry, using ammonia as probe molecule. The acidic characteristics of the samples were shown to be strongly affected
by the preparation method, calcination temperature, and sulfur content. The samples prepared by sol–gel and mechanical grinding
exhibited higher acidity than co-precipitated samples. Moreover, increasing the calcination temperature of co-precipitated
samples resulted in a decrease in surface area from 402 to 57 m2 g−1 and sulfur content from around 4 to 0.2 mass%, but up to a certain point generated a stronger acidity. The optimal calcination
temperature appeared to be around 673 K.