Preparation of a highly active Fe-ZSM-5 catalyst through solid-state ion exchange for the catalytic decomposition of N2O

This work describes a new and simple preparation method for Fe-ZSM-5 pentasil-zeolites through solid-state ion exchange process. The zeolite catalysts thus prepared exhibit high activity during the catalytic decomposition of N2O in the absence of reducing agents. The aimed choice of using FeSO4 x 7H(2)O and NH4-ZSM-5 as starting materials consisted of forming such products (ammonium salts) after the ion exchange process that can be completely removed through thermal treatment. The complete preparation process leading to the formation of catalytically active iron species inside the zeolite takes place in two steps at two distinguished temperatures, respectively. The first step during which the solid-state ion exchange takes place has been carried out through two different routes, in air and in vacuum, in search for an enhanced catalytic activity. The second step has to be necessarily done under anaerobic conditions. XRD measurements have revealed the presence of hematite in samples with a Fe(II)/Al ratio above 0.5. The different numbers of Bronsted sites occupied by the iron species in the catalysts with different Fe contents have also been determined. (C) 1999 Elsevier Science B.V. All rights reserved.