Journal of Catalysis 221 (2004) 560–574 www.elsevier.com/locate/jcat Effect of high-temperature treatment on Fe/ZSM-5 prepared by chemical vapor deposition of FeCl 3 I. Physicochemical characterization E.J.M. Hensen, a,∗ Q. Zhu, a M.M.R.M. Hendrix, b A.R. Overweg, c P.J. Kooyman, d M.V. Sychev, e and R.A. van Santen a a Schuit Institute of Catalysis, Laboratory of Inorganic Chemistry and Catalysis, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven, The Netherlands b Laboratory of Solid State and Materials Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands c Interfacultair Reactor Institute, Delft University of Technology, Mekelweg 15, 2629 JB, Delft, The Netherlands d National Centre for High Resolution Electron Microscopy, Delft University of Technology, Rotterdamseweg 137, 2628 AL Delft, The Netherlands e National Technical University of Ukraine, Faculty of Chemical Technology, pr. Peremogy 37, 03056 Kiev, Ukraine Received 30 June 2003; revised 19 September 2003; accepted 24 September 2003 Abstract The effect of severe (hydrothermal) treatment on Fe/ZSM-5 prepared by sublimation of FeCl 3 is studied by a combination of high- resolution TEM, EXAFS, 57 Fe Mössbauer spectroscopy, IR, UV–vis, nitrogen adsorption, 27 Al NMR spectroscopy, and low-temperature nitrous oxide decomposition. The heterogeneous nature of Fe/ZSM-5 is stressed with a preponderance of iron oxide particles on the external zeolite surface. Additionally, neutral iron oxide nanoparticles and charge-compensating iron complexes are located in the micropores. Severe calcination at 973 K induces the growth and ordering of the iron oxide aggregates. Moreover, some of the occluded neutral iron oxide nanoparticles are transformed into charge-compensating iron complexes upon a protolysis reaction with the Brønsted protons. These effects are more pronounced in the case of steaming at 973 K, additionally resulting in the removal of Al from framework positions. Despite the low dispersion of iron oxide in Fe/ZSM-5, relatively low Fe–Fe coordination numbers were derived from the EXAFS data for Fe/ZSM-5; high-temperature treatments increased this number. This low value points to the disordered nature of the iron oxide aggregates rather than to the presence of an abundant fraction of binuclear iron clusters. Titration of sites active in nitrous oxide decomposition shows that their amount increases upon increasing severity of treatment of Fe/ZSM-5. Their number, however, remains very small (a few percent of the total iron) and appears to correlate to the amount of Fe 2+ present after room temperature exposure to vacuum conditions. A comparison to a commercial HZSM-5 zeolite with a very low iron content is made. The catalytic performance of these materials is discussed in a companion paper (J. Catal. (2003)).  2003 Elsevier Inc. All rights reserved. Keywords: Fe/ZSM-5; Sublimation method; Active sites; Nitrous oxide decomposition; Mössbauer spectroscopy; Extended X-ray absorption fine structure; Infrared spectroscopy; Nuclear magnetic resonance 1. Introduction The limited dimensions of zeolite micropores allow sta- bilization of small transition metal oxide complexes with unique catalytic properties [1,2]. The redox properties of iron-containing zeolites, most notably with the MFI topol- ogy, have attracted widespread attention for a number of * Corresponding author. E-mail address: e.j.m.hensen@tue.nl (E.J.M. Hensen). potential catalytic applications. Most importantly, such ze- olites catalyze the selective insertion of an oxygen atom into the C–H bonds of aromatics and alkanes [3] when nitrous oxide is the oxidant. The particular case of benzene hydroxy- lation to phenol forms the basis for a potential alternative [4] to the environmentally stressing three-step cumene process. Moreover, these materials may be suitable for abatement of nitrous oxide emissions from nitric acid plants [5–10]. An- other potential application field is NO x reduction for diesel or lean-burn Otto engines, which has resulted in a number of 0021-9517/$ – see front matter  2003 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2003.09.024