Catalytic NOx reduction by carbon supporting transition metals (Fe, Co, Ni, Cu) and potassium has been studied. The effect of oxygen on the catalytic properties of the metals has been analyzed. Temperature-programmed reactions and isothermal reactions have been conducted in a fixed bed flow reactor. Temperature-programmed reduction in hydrogen, XRD and XPS have been used to characterize the catalysts. All the metals studied catalyze the NOx reduction by carbon in the presence of oxygen, but also the O-2-carbon reaction. Metal catalytic activity is the result of two factors, the tendency of the metal to be oxidized by NO and the easiness of the resulting oxide to be reduced by carbon. Among the metals studied, nickel exhibits the highest selectivity for NOx reduction. The results of this study strengthen the possible benefit of the lack of a gaseous reducing agent (such as ammonia or hydrocarbons) since the reduction of NOx is performed by the carbon support itself.