Study of the Fe/zeolite-L system -: Part I:: Characterization of iron species and their structural properties

Zeolite-L in potassic (ZLK) and acidic (ZLH) forms were used as a support for iron species to obtain two solids, called Fe/ZLK and Fe/ZLH, respectively. "In situ" Mossbauer spectroscopy (MS) between room temperature (RT) and 15 K, volumetric oxidation (VO) and thermogravimetric analyses were used to determine the iron species existent after reduction (Fe-0, Fe2+ and Fe3O4) and to study their structural properties. In both solids, a similar fraction of very small Fe-0 crystals was found inside the zeolite channels. Intermediate species, like exchanged Fe2+, were also detected in both samples. It was possible to determine that Fe2+ ions are located at sites D in Fe/ZLK and sites A in Fe/ZLH. Soft reduction conditions, Like slow temperature raise (2 K/min), allowed to maintain metallic Fe crystals inside the zeolite-L structure in contrast with other Fe/zeolite systems. (C) 2000 Elsevier Science B.V. All rights reserved.