DEALUMINATION OF FAUJASITE, MAZZITE, AND OFFRETITE WITH AMMONIUM HEXAFLUOROSILICATE

Synthetic faujasite, mazzite, and offretite have been dealuminated with ammonium hexafluorosilicate. The products have been characterized by elemental analysis, X-ray diffraction, volumetry, scanning electron microscopy, stepwise thermal desorption of ammonia, solid-state NMR and IR spectroscopy. Their catalytic activity has been evaluated using isooctane cracking as test reaction. The maximum level of dealumination which can be achieved without loss of X-ray crystallinity corresponds to 50% for faujasite and 30% for mazzite and offretite. This result and the fact that the dealumination capability depends on the texture of the crystals suggest that the reaction is diffusion controlled. The comparison of the acidic and catalytic properties of the parent and dealuminated samples shows small differences indicating that the fluorosilicate treatment replaces weakly bound and weakly acidic aluminium atoms. © 1990.