The activity of potassium-bimetallic catalysts (KFe, KCo, KNi and KCu) for NOx reduction by carbon has been studied. Temperature-programmed reactions and isothermal reactions have been carried out in a fixed bed flow reactor using a 0.5% NO/5% O-2/He mixture. The addition of a transition metal to a potassium catalyst enhances its activity showing a synergetic effect. Temperature-programmed desorption experiment in helium reveals that the temperature for transition metal reduction by carbon decreases in the presence of potassium. Among the combination of metals analyzed, the KNi is most interesting because it combines a high NOx reduction capacity, at low temperatures, with the lowest loss of carbon by combustion. (C)2000 Elsevier Science B.V. All rights reserved.