A V2O5-based catalyst obtained by grafting vanadyl tri-isopropoxide on a TiO2-SiO2 support obtained by grafting titanium alkoxide on silica has been studied as to the selective catalytic reduction (SCR) of NO with ammonia. The performances obtained have been compared with those of other catalysts in which V2O5 was supported, respectively, on the same support by impregnating it with ammonium vanadate and on TiO2 both by grafting vanadyl tri-isopropoxide and by impregnating it with ammonium vanadate. The first mentioned catalyst turned out to be the best as to activities and selectivities. All the used catalysts and supports have been characterised using many techniques in order to explain the different performances observed. As it will be seen, activities and selectivities, in the mentioned reaction, are mainly affected by three factors that are: (i) V2O5 dispersion largely favoured by the grafting technique; (ii) the morphological properties of TiO2 surfaces that cannot be foreseen but only investigated when TiO2 is obtained by grafting titanium alkoxide on the surface of another oxide and (iii) the type of surface acidity, retaining ammonia reagent.