EVOLUTION OF FE3-FRAMEWORK SPECIES IN FE-SILICATE AS A FUNCTION OF THE TEMPLATE BURNING TEMPERATURE( FROM FRAMEWORK TO EXTRA)

We report a XAFS study of the Fe3+ 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 NH3 Our XAFS results show that, before template b urning, Fe3+ are in tetrahedral symmetry with 4 oxygens at 1.85 Angstr om, while after template removal and in vacuum conditions, they exhibi t a distorted tetrahedral symmetry with 3 oxygens at 1.87 Angstrom, an d one at 2.10 Angstrom; dosage of NH3 partially restore the tetrahedra l symmetry of the site. These results are strongly supported by parall el IR, Raman, UV-Vis, TPR and EPR investigations and by recent theoret ical simulations.