STRUCTURAL EVOLUTION OF DEALUMINATED Y-ZEOLITES DURING KOH SOLUTION TREATMENT

H(4)EDTA- and (NH4)(2)SiF6- liquid phase dealuminated Y zeolites (EDY and FDY) and hydrothermally dealuminated Y zeolites (USY) were treated with an aqueous solution of KOH. The products were characterized by u sing XRD, n.m.r., FT i.r., SEM, and fast atom bombardment mass spectro scopy (FABMS) techniques. A decrease of Si/Al ratios was observed in t he basic solution-treated samples. The results clearly show that disso lution of the surface of EDY and removal of silicon atoms from the fra mework lattice of FDY occurs during basic solution treatment. Realumin ation of ultrastable Y zeolite (USY) takes place through reinsertion o f aluminum into the framework vacancies formed during hydrothermal tre atment of NH4NaY or formed during a basic solution treatment of USY. ( C) Elsevier Science Inc. 1997.