Unveiling the Structural Characteristics of Intergrowth Zeolites Synthesized in the Presence of Isopropylimidazolium-Based Cations and Fluoride Anions

Abstract

Here, we present the synthesis of RTH/ITE and MEL/MFI intergrowth zeolites using 2-isopropylimidazolium-based cations as organic structure-directing agents (OSDAs) in concentrated fluoride media and their local structural properties. Phase selectivity in the synthesis of zeolite intergrowths was found to differ according to the concentration of OSDA cations and fluoride anions in the synthesis mixture as well as to the type of OSDA employed. Molecular modeling results suggest that the crystallization of intergrowth zeolites in fluoride media may be kinetically rather than thermodynamically controlled, as in ordered zeolites. Cs-corrected STEM analysis of MEL/MFI crystals synthesized at HF/OSDA = 2.0 in the presence of 2-isopropyl-1,3-dipropylimidazolium ions as an OSDA indicates the existence of previously unobserved MEL-MFI intergrowth along the [100] direction, leading to a partial blockage of MEL 10-ring channels.

The Current Understanding of Mechanistic Pathways in Zeolite Crystallization

“…The third type involves intergrowths (Figure c), which typically require a high degree of similarity between the two zeolite structures. The benefits of intergrown zeolites include enhanced particle morphologies (e.g., self-pillared and other hierarchical architectures , ) and the possibility of combining two different framework structures into a product with unique properties, such as MEL/MFI, CHA/AEI, , FAU/EMT, or RTH/ITE intergrowths. In many cases, this type of IZT requires the use of specific OSDAs, which was highlighted in a collaborative study by Gómez-Bombarelli, Corma, Moliner, and Román that established a database to facilitate OSDA selection for intergrowth design .…”