Control of Na-EMT Zeolite Synthesis by Organic Additives

Organic additives were used to control the formation of EMT-type zeolite in a sodium-rich initial system. Triethanolamine was employed as a nucleation suppression agent able to complex the aluminum during the synthesis of the EMT-type zeolite. The commonly used tetramethylammonium (TMA) chloride and tetraethylammonium (TEA) chloride as structure directing agents in zeolite synthesis were also employed in this study. The triethanolamine has the most pronounced effect on the crystal growth process of the EMT-type zeolite. The use of triethanolamine resulted in the formation of large crystals (100 nm) with the framework composition different from the counterpart obtained in the organic-free system. Therefore, the function of triethanolamine is attributed to the immobilization of Al in the initial gel and thus partial suppression of zeolite nucleation. The immobilization of a part of Al resulted in the EMT zeolite crystals with a higher Si/Al ratio (1.4). In contrast, the TMA and TEA organic additives have a limited impact on the physicochemical properties of the EMT crystals, the latter being a consequence of large presence of Na in the system. The bulky TMA and TEA ions prevent the aluminosilicate precursor species from agglomeration and formation of dense gels and thus resulting in the crystallization of nanosized EMT zeolite crystals (10-20 nm).