HYDROTHERMAL SYNTHESIS OF GALLOALUMINOSILICATE (MFI) ZEOLITE CRYSTALSHAVING UNIFORM SIZE, MORPHOLOGY AND GA AL RATIO/

The hydrothermal synthesis of galloaluminosilicate (MFI) zeolite from a gel containing a source of silica (Na-trisilicate), a source of gall ium (Ga-nitrate or Na-gallate), a source of aluminum (Al-nitrate or Na -aluminate), a templating agent (TPA-Br), deionized water, and sulfuri c acid has been thoroughly investigated to know the influence of vario us synthesis parameters (viz., the source of Al and Ga, gel compositio n, pH of the gel, and crystallization temperature) on the size and mor phology of the zeolite crystals formed and also on the Al and Ga conte nt (or Ga/Al ratio) of individual crystals. The zeolite samples were c haracterized for their bulk composition by chemical analysis, for thei r crystalline nature by XRD, for crystal size and morphology by SEM, a nd for the Ga/Al ratio of the individual crystals by EDS analysis. The morphology and Ga/Al ratio of zeolite crystals are strong ly influenc ed by the source of Ga and also by the pH of the synthesis gel. The us e of Na-gallate (as a source of Ga) with Na-aluminate or Al-nitrate (a s a source of Al) and pH of gel = 7-9 results in zeolite crystals with a uniform shape/morphology (spherical-hexagonal) and Ga/Al ratio. The use of Ga-nitrate as a source of Ga, however, results in zeolite crys tals with two different shapes, spherical crystals with a high Ga/Al r atio and hexagonal crystals with a low Ga/Al ratio. (C) Elsevier Scien ce Inc. 1997.