In order to interpret catalytic data on iron zeolites in terms of structure-activity relationships, reliable characterisation methods are needed. In particular, the nuclearity of the iron species is an important issue, since it is often invoked to explain catalytic activity. In the present contribution, we address the problem of the nuclearity of the iron species in Fe-ZSM-5 by a combination of techniques, that is, UV-Vis, EXAFS, Magnetic Circular Dichroism (MCD) and magnetisation measurements. Based on an in-depth analysis of these data, we show that some of the current interpretations of UV-Vis and EXAFS spectra need to be revised.

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