Fabrication zone of OSDA-free and seed-free mordenite crystals

Abstract Direct hydrothermal synthesis of mordenite without the addition of both seed and organic template is reported in this work. The role of inorganic cations in the crystal purity and directing the mordenite structure were studied. It was observed that higher Si/Al ratio requires higher alkalinity of the gel. Pure mordenite was obtained using silica gel, colloidal silica and fumed silica. Amorphous material was obtained using tetraethyl orthosilicate (TEOS) due to dissolution problem of TEOS in water. It was also observed that crystal size decrease with decrease in crystallization temperature. The Si/Al ratio can be raised to as high as 50 using silica gel in template-freeprocess. At fixed Na/Si ratio of 0.52, pure mordenite with ratios Si/Al of 15 and 25 could be obtained. Fumed silica favours the formation of rod-like crystals.