Crystallization of Mordenite Platelets using Cooperative Organic Structure-Directing Agents

Area of Science:

• Materials Science
• Crystallography
• Catalysis

Background:

• Organic structure-directing agents (OSDAs) are crucial for synthesizing zeolites with tailored properties.
• Typically, single OSDAs are used, but synergistic effects of multiple OSDAs are less explored.
• Understanding OSDA-zeolite interactions is key to rational design.

Purpose of the Study:

• To investigate the cooperative effect of two distinct OSDAs in zeolite synthesis.
• To characterize the resulting zeolite structure and the arrangement of OSDAs within it.
• To evaluate the catalytic performance of the synthesized zeolite.

Main Methods:

• Synergistic synthesis using N,N,N-trimethyl-1,1-adamantammonium and 1,2-hexanediol.
• Synchrotron X-ray diffraction with Rietveld refinement for structural analysis.
• Molecular modeling (molecular dynamics) for predicting OSDA arrangement and packing.
• Solid-state NMR spectroscopy (2D 27Al{29Si}, 27Al{1H}, 13C{1H}) for OSDA interactions.
• High-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) for morphology and crystal facet analysis.

Main Results:

• Cooperative synthesis yielded a new zeolite structure, HOU-4, with the mordenite (MOR) framework type.
• Rietveld refinement and molecular modeling revealed specific spatial arrangements of the OSDAs within the zeolite channels and pockets.
• Experimental and computational data confirmed favorable OSDA packing and loading.
• Characterization confirmed the formation of ultrathin, nonfaulted HOU-4 crystals with a platelike morphology.
• HOU-4 crystals exhibited enhanced catalytic activity for cumene cracking compared to conventionally synthesized mordenite.

Conclusions:

• The combination of two specific OSDAs leads to cooperative structure-direction, yielding a novel zeolite (HOU-4).
• The precise arrangement and interaction of co-existing OSDAs are critical for directing zeolite formation.
• This approach enables the synthesis of advanced zeolite materials with improved properties and performance, opening new avenues for dual OSDA applications.