COMPARISON OF CRYSTALLIZATION RATES OF [AL]-MFI-TYPE AND [GA]-MFI-TYPE ZEOLITES

The crystallization rates of [Al]- and [Ga]-MFI-type zeolites were stu died at 170-degrees-C and autogeneous pressure. Samples were character ized by XRD, FTi.r. solid-state Al-27 and Ga-71 MAS n.m.r., and X.p.s. techniques. Results clearly show that the crystallization rate of [Ga ]-ZSM-5 is much faster than that observed for [Al]-ZSM-5. Whereas [Ga] -ZSM-5 is synthesized in just 4 h, [Al]-ZSM-5 is synthesized in 40 h u nder the same conditions. This is probably due to the fact that, under alkaline conditions, free gallate ions are more stable than are alumi nate ions.