THE EFFECT OF THERMAL-TREATMENT AND OF GRINDING ON SILICALITE-1 SYNTHESIZED IN THE PRESENCE OF FLUORIDE IONS

Synthesis in fluoride-containing medium leads to large silicalite crys tals without SiOX defect groups. The four occluded tetrapropylammonium (TPA(+)) ions/unit cell are ion pairs with 2 F- and 2 OH-. Grinding t he samples in the presence of water leads to SiOH groups that are elim inated during calcination. The two endothermic peaks at 420 and 560 de grees C of the TPA(+) decomposition are identified as being due to the Hoffmann degradation of the TPA(+) ion (first peak) and to the decomp osition of the products of TPA(+) ion (second peak).