Evolution of Fe3+ from Framework to Extra-Framework Species in Fe-Silicate as a Function of the Template Burning Temperature

We report a XAFS study of the Fe 3+ local environment in Fe-silicalite as a function of the template burning temperature. We investigate the structural changes of the zeolitic structure, upon thermal treatments and interaction with NH 3 . Our XAFS results show that, before template burring, Fe 3+ are in tetrahedral symmetry with 4 oxygens at 1.85 A, while after template removal and in vacuum conditions, they exhibit a distorted tetrahedral symmetry with 3 oxygens at 1.87 A, and one at 2.10 A; dosage of NH 3 partially restore the tetrahedral symmetry of the site. These results are strongly supported by parallel IR, Raman, UV-Vis, TPR and EPR investigations and by recent theoretical simulations.