THE SYNTHESIS OF SILICALITE-2 AND SILICA-ZSM-48 FROM HYDROGELS CONTAINING TETRABUTYLAMMONIUM BROMIDE, HEXAMETHONIUM BROMIDE, AND DIAMINODODECANE IN THE PRESENCE OF FLUORIDE IONS

Silica gels containing tetrabutylammonium bromide (TBABr), hexamethonium bromide (HMBr2), and 1,12-diaminododecane (DADD) have been prepared in fluoride medium. The gels of composition 10 NaF-(xTBABr-yHMBr2-zDADD)-10 SiO2-330 H2O with x + y + z = 1.25 crystallize to either silicalite-2 or ZSM-48. The crystallization fields and reaction rates have been systematically examined as a function of the organic content, the amount of F- ions, and the nature of inorganic cations (Li+, Na+, K+, NH4+ and Ca2+). Long needles of ca. 200-mu-m were obtained for silicalite-2 in certain organic composition ranges. Different thermal analysis decomposition maxima were found for the needles and for the ovate-shaped crystals. TBA is the main occluded species in silicalite-2, whereas ZSM-48 contains mainly DADD.