The steady-state catalytic redn. of NO with CO on iron oxide was described with three different models, which all fit the exptl. data equally well. By applying the transient method to this reaction, it has been shown that for reduced catalysts without adsorbed CO, the N2O redn. step is well described qual. by two of the models, whereas only one of them can describe the NO redn. step. In the presence of adsorbed CO, however, none of these models can explain the obsd. transient behavior. Therefore, a modification of the best model was proposed and tested via computer stimulation, which showed good agreement with transient expts. [on SciFinder (R)]