Synthesis of hexagonal aluminosilicate from liquid-crystalline mesophase using zeolitic nanoclusters: bottom-up versus top-down approach

Abstract

An amorphous porous hexagonal aluminosilicate Al-ZAT was prepared using liquid crystal phase of Brij-56 and preformed MFI zeolite nanoclusters solution through bottom-up approach. The HCl concentration (0.5–2.0 M), HCl to Brij-56 ratio and zeolitic seed solution wss varied for the mesoporous system at ambient synthesis condition. The optimum Brij-56 to HCl ratio was found to be 1 Brij 56: 9–19 HCl (0.5 M) by mass. The addition of preformed zeolite seed (7–14 ml) as precursor solution instead of conventional silica source tetramethyl orthosilicate (TMOS) generate uniform mesophase and subsequently avoids formation of methanol (from TMOS hydrolysis) that affects liquid crystalline mesophase. MCM-41 (ZMCM-41) and SBA-15 (ZSBA-15) derived from similar zeolite precursor solution was synthesized for comparative study. The porous textural characteristics, and type of surface acidity were studied. The analysis showed a highly porous hexagonal structure of Al-ZAT. ZMCM-41 prepared through top-down approach, showed formation of ordered nanostructured mesoporous (disordered hexagonal). Al-ZAT and ZSBA-15 shows weaker Bronsted acid sites compared to ZMCM-41.