The reduction of NO with CO on Ni-impregnated active carbon catalysts (AC/Ni) has been investigated. High activity toward NO reduction can be achieved on an AC/Ni catalyst obtained by thermal decomposition of the precursor nitrate at 200 degrees C. The role of active carbon in the catalytic reduction of NO with CO at different temperatures has been discussed. At low temperatures (below 200 degrees C), when there is no substantial gasification of the carbon, dissociative adsorption of NO along with Nz evolution and oxygen accumulation on the carbon surface has been observed, The active sites occupied by the oxygen evolved during the NO decomposition are regenerated by the CO reducing agent. At high temperatures the C-O complexes evolved from the carbon surface participate in NO reduction as a second reducing agent. The effect of the oxygen-containing functional groups and the available nitrate groups on catalyst activity has been discussed.