A systematic investigation of the effect of various metal oxides additives on the reactivity of a I wt% V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NO by NH3 has been carried out at 623 It. Activity measurements were conducted in a simulated flue gas containing H2O and SO2, and indicated that the activity of the V2O5/TiO2 catalyst can be significantly affected by the presence of an additional metal oxide. MoO3 and WO3 were found to have the biggest promoting effect, while ZnO was found to have the biggest poisoning effect. The structure of the surface vanadia species, as well as of same of the other transition metal oxides, was characterized by in situ Raman spectroscopy. Ammonia-temperature programmed desorption (NH3-TPD) was used to probe the reducibility and total acidity of the different catalysts. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to probe: the type of the different acid sites on the catalyst surface. The analysis of our results suggests a strong correlation between the SCR activity and the amount of Bronsted acid sites on the catalyst surface.