Reaction of HY zeolite with molecular fluorine

At room temperature, gaseous Fi extracts tetrahedrally coordinated aluminum from the lattice of an acid, near-faujasite HY zeolite (Si/Al approximate to 13) and forms fluoro-hydroxy-aluminum complexes of the type Al2F(OH)(n)( (5-n)+) in which Al is octahedrally coordinated. Moreover, the crystallinit y of the zeolite is almost unchanged by the fluorination process. The HY de hydrated at 200 degreesC under vacuum and treated under a F-2 pressure of 3 00 mbar at room temperature is practically totally dealuminated. At lower p ressure the transformation is partial. The coordination shell of the comple x becomes unstable at about 500 degreesC. Upon losing ligands, octahedral A l reverts partially to the tetrahedral coordination and is partially reinse rted into the lattice. At a higher temperature an amorphous alumina phase i s formed. Al-27 and F-19 high-resolution solid-state NMR, FT-IR, X-ray diff raction, and temperature-programmed desorption (TPD) are the main tools use d in this work. (C) 2001 Academic Press.