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Synthesis and characterization of gallosilicate MFI-type zeolites: effect of the gel composition on the crystallization rate

Abstract:

Gallosilicate MFI-type zeolites ([Ga]-ZSM-5) were synthesized at 170°C, with autogeneous pressure and agitation. Samples were characterized by 71Ga MAS n.m.r., XRD, i.r., X.p.s., and chemical analysis. The influence of synthesis parameters such as the SiO2 Ga2O3, (TPA)2 O SiO2, and Na2O SiO2 gel molar ratios on the crystallization kinetics were evaluated. Pure and highly crystalline [Ga]-ZSM-5 are formed after 20-24 h heating, independently of the gel composition, provided that traces of the template agent (tetrapropylammonium ions, TPA+) are present. Such particular behavior is related to the presence of very stable monomer gallate ions in the alkaline synthesis media that are readily incorporated in the MFI framework structure, irrespective of low oligomeric hydroxy-Al species present in similar conditions. © 1994.