SYNTHESIS AND CHARACTERIZATION OF GALLOSILICATE MFI-TYPE ZEOLITES - EFFECT OF THE GEL COMPOSITION ON THE CRYSTALLIZATION RATE

Gallosilicate MFI-type zeolites ([Ga]-ZSM-5) were synthesized at 170 d egrees C, with autogeneous pressure and agitation. Samples were charac terized by Ga-71 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 kineti cs were evaluated. Pure and highly crystalline [Ga]-ZSM-5 are formed a fter 20-24 h heating, independently of the gel composition, provided t hat traces of the template agent (tetrapropylammonium ions, TPA(+)) ar e 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 l ow oligomeric hydroxy-Al species present in similar conditions.