Alkaline treatment of Fe-ZSM-5 zeolite induces substantial intracrystalline mesoporosity and enhances the population of isolated Fe3+ at the expense of oligonuclear clusters. In situ UV/vis showed that this redispersion affects the redox properties of the alkaline-treated zeolite and leads to lower activity in direct N2O decomposition compared with the parent sample. Subsequent ion exchange of the alkaline-treated sample in ammonium nitrate solutions induced a renewed alteration in iron speciation, resulting in a similar constitution as in the parent zeolite but with a higher concentration of Fe2+ sites able to activate N2O. Mechanistic investigations in the TAP reactor furthermore affirmed that these newly obtained species had improved oxygen desorption, which correlates with the superior activity in direct N2O decomposition. (c) 2006 Elsevier Inc. All rights reserved.