Diquaternary structure-directing agents built upon charged imidazolium ring centers and their use in synthesis of one-dimensional pore zeolites

Abstract

A series of diquaternary organo-cations, structure-directing agents (SDA), were prepared from imidazole rings connected by methylene chains of various lengths. These were tested in zeolite syntheses to determine if four different one-dimensional pore system zeolites (MTT, TON, MTW and ZSM-48) could accommodate the changes in the positioning of the imidazolium ring that bears the charged nitrogen. We were able to demonstrate that there is flexibility in the methylene chain length for all of the zeolites except MTT, which apparently has more rigid demands concerning the fit of the SDA. While subsequent calculations showed which chain lengths should provide better fits of the SDA within the MTT framework, the syntheses with these SDA still did not yield MTT phases. This raised some issues concerning the dominance of kinetic factors over our thermodynamic considerations in zeolite synthesis.