Synthesis of Siliceous Mordenites and Their Properties

Abstract

Siliceous mordenites were synthesized from aqueous clear solutions of sodium aluminosilicates containing benzyltrimethylammonium (BTMA), at 100° under atmospheric pressure. Their SiO₂/Al₂O₃ ratios (R value) of framework were in the range from 14.7 to 25.8. With increase of the R value, the crystals grew platy in habit rather than prismatic.
BTMA was occluded in the large cavity composed of 12-membered rings of (AlO₄) and (SiO₄) tetrahedra, and could not be exchanged by other cations. The number of Na⁺ions in the cavity probably decreases by the occlusion of the large organic base. Ac-cording to the relation, Na⁺Al₃⁺=Si⁴⁺, the number of (AlO₄) tetrahedra decreases, whereas that of (SiO₄) tetrahedra increases. Consequently, the organic base appears to cause the increase of R value.
The degree of ion exchange for sodium in Na form was high for univalent cations as compared with divalent ones.
From the experimental results of the adsorption of water vapor on the Na forms and ion exchange ones, it is concluded that mordenite becomes hydrophobic with increasing of R value, and their adsorption properties seem to change remarkably in the vicinity of 21-22 in R value.