Carbon-coated catalysts doped with tungsten and vanadia oxides with different V and W loadings have been prepared by the ionic exchange method and characterized. The surface, structure and composition have been investigated by XPS, Raman, N-2 sorption at 77 K, TPD-NH3 and reactivity tests for the SCR of NO with NH3 at low temperatures. Under reaction conditions, NO conversions were found to go through a maximum with vanadia surface coverage at approximately half a monolayer. The observed decrease in the SCR activity at higher vanadia loadings can be attributed to either a loss of dispersion or loss of textural properties. Maximum NO conversion is ascribed to the higher Bronsted proton acidity (V4+) of the centres that decreases with increasing vanadia loadings up to 3 wt% loading due to the increase of V4+/V5+ ratio. Large amounts of tungsten (5%, w/w) upon or before addition of vanadia do not provide an enhancement of activity. The results indicate that W addition increases surface acidity leading to stronger Bronsted or even Lewis acid centre creation. (C) 2009 Elsevier B.V. All rights reserved.