The influence of treating carbon with sulphuric and nitric acids on the activity of a carbon-based briquette catalyst for NO reduction with NH3 was examined in a fixed-bed reactor at low temperature (150 degrees C). The briquette catalysts were prepared from a low-rank coal and a commercial tar pitch. The active phase was impregnated from a suspension of ashes of coke petroleum by means of an equilibrium adsorption method. The catalytic behaviour of NO reduction over acid treated briquettes was found to vary with the surface characteristics of the carbon support. This suggests that the number of oxygen-containing sites as well as vanadium load and dispersion affect the reaction activity. In the presence of oxygen, the SCR activity is enhanced with a nitric acid treatment, activity is promoted by the presence of acidic surface groups such as carboxyl and lactone, which can help not only to create a reservoir of reactants on the catalysts surface but also to improve the dispersion or even increase the amount of vanadium loading. Therefore, the results of this study suggest that the formation of acidic sites on the surface is an important step for NO reduction with NH3 over carbon-based catalysts. Additional techniques such as XPS and TPD to characterize the oxygen surface and those such as N-2 adsorption to characterize the textural properties were also used in this study. (C) 2007 Elsevier Ltd. All rights reserved.