A Versatile Organic Structure-Directing Agent Unlocks Diverse Zeolite Structures: A Systematic Exploration of 2-n-propyl-1,3-dimethylimidazolium in Zeolite Synthesis

Organic structure-directing agents (OSDAs) play an important role in zeolite synthesis, enabling the discovery of novel structures and compositions. While highly specific OSDAs have been traditionally favored, recent studies have highlighted the potential of less specific OSDAs in combination with other structure-directing effects. This study presents a systematic investigation of the zeolite phase space accessible through the use of 2-n-propyl-1,3-dimethylimidazolium (2nPr13DMI) as an OSDA. Our findings reveal a remarkably rich landscape encompassing eight distinct zeolite structures: -SYT, -CLO, STW, CSV, ITW, STF, MTW, and IM-18. Additionally, two new layered phases, HPM-22 and HPM-23, were synthesized and then transformed upon calcination into zeolites MTF and HEU, respectively. Of particular interest is the synthesis of the high silica extra-large pore -SYT interrupted framework with significantly reduced germanium content (Gef = 0.1 compared to over 0.3 in prior reports). Despite this enhanced composition, the stability of the zeolite is still poor, likely due to the large content of dangling Si-OH groups in this interrupted framework. This work demonstrates the potential of using less specific OSDAs in zeolite synthesis and highlights the complex interplay between OSDA structure, synthesis conditions, framework composition, and material stability.