Dual organic-structure directing agents in the synthesis of high-silica MOR Zeolite: Cooperation or competition?

Constructing a high-silica framework of a given zeolite topology via a conventional hydrothermal synthetic strategy is still an open question. In this work, In this contribution, we report the high-silica MOR zeolite (Si/Al ratio: ∼30) was fabricated by a dual OSDA combination strategy at a fixed alkalinity (OH⁻/SiO₂) ratio of around 0.4. Additionally, we found that bulky TEA⁺ cation and smaller neutral heterocycle molecules severed as the pore-filling agent and cooperatively squeeze the occupation of sodium cation resulting in the low sodium content of high-silica MOR zeolite. However, such cooperative behavior can be easily spoiled by the high alkalinity ratio above 0.5. With the increment of the alkalinity ratio, the sodium cations can retake the occupied sites and facilitate the MOR framework with a relatively low Si/Al ratio. As unveiled by the powder X-ray diffraction crystallography and combined spectroscopy strategies, the nature of different dual OSDA combinations occluded in the high-silica MOR zeolite with deduced aluminum enriched T sites provide the reference for the forthcoming target design of zeotype catalysts.