Redn. of NO and N2O by CO over a SiO2-supported iron oxide catalyst was studied by the transient response method, with different initial oxidn. states of the catalyst, i.e., completely reduced (Fe3O4), or oxidized (Fe2O3). The affect of CO pre-adsorption was also studied. From the material balance on the gas-phase species, it was shown that the compn. of the catalyst changes during relaxation to steady-state. The degree of redn. of the catalyst at steady-state could thus be estd. During the transient period, CO was shown to inhibit N2O as well as NO redns. by adsorption on reduced sites. Activity of the reduced catalyst was substantially higher as compared to the oxidized catalyst for both reactions. On this basis, it was attempted to keep the catalyst in a reduced state by periodically reducing it with CO. As a result, a significant increase in reactor performance with respect to steady-state operation could be achieved for N2O redn. by CO. Finally, the dynamic behavior of the N2O-CO and NO-CO reactions made it possible to evidence reaction steps, the occurrence of which could not be shown during previous investigations on the sep. interactions of the reactants with the catalyst. [on SciFinder (R)]