Adsorption of nitric oxide was studied over reduced and unreduced Fe, Cu, Co and Ni impregnated activated carbons (AC) in a microreactor system in the presence and absence of oxygen. In the absence of oxygen reduced Fe-AC showed an NO removal efficiency of 58% which was higher than that of virgin activated carbon by a factor of 2.5. The removal efficiency of Cu-AC with and without oxygen was in the range of 44-46%.