Seed-assisted crystallization of high-silica cubic and hexagonal faujasite polymorphs in the presence of the tetraethylammonium (TEA+) cation

Silica-rich Y (FAU topology) and EMC-2 (EMT topology) zeolites have been obtained in the presence of the tetraethylammonium (TEA(+)) cation as a structure-directing molecule and the corresponding protonic zeolites as seeds. In the presence of USY seeds, Y zeolites were fully crystallized after a few hours at 130 degrees C but they were unstable and rapidly converted into chabazite, a zeolite with CHA topology. Their stability could nonetheless be greatly improved by decreasing the temperature to 110 degrees C without significantly modifying the morphology of the crystals and the composition of the framework. Framework SiO2/Al2O3 ratios up to 13 could be obtained, which is the highest value ever reported for Y zeolites synthesized with TEA(+) cations as the sole organic molecule. The use of H-EMC-2 as seeds generally led to FAU-EMT intergrowths in which the relative proportion of EMT depended on the composition of the seeds. However, a pure EMT zeolite could be obtained under specific conditions. With a framework SiO2/Al2O3 ratio of 11.2, it constitutes the first example of Si-rich EMT obtained in the absence of crown ether from conventional silica and alumina sources.