The reaction of Fe-zeolites prepared by sublimation of FeCl3 with N2O was studied by step- and pulse-response experiments. Steps from 0 to 5000 ppm N2O were performed at 673 K, after pretreatment of the catalyst in H-2, He, or O-2. When the catalysts were prereduced in H-2, N2O was first consumed for the reoxidation of the catalyst, before steady-state N2O decomposition started. Also pretreatment in He reduced the catalyst. This autoreduction was not spontaneous, but caused by a small amount of hydrocarbons adsorbed on the catalyst. Prereduced catalysts had a higher steady-state activity, indicating that the incorporation of oxygen from N2O changed the structure of the active sites. Pulse responses proved that O-2 desorption is the rate-limiting step of N2O decomposition. O-2 desorption was relatively fast from a small fraction of sites, while a second oxygen pool desorbed only slowly from the catalyst. Only the former is responsible for catalytic activity. (C) 2003 Elsevier Inc. All rights reserved.