Calorimetric study of the acidic character of V2O5-TiO2/SO4 2- catalysts used in methanol oxidation to dimethoxymethane

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 m(2) 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.