Discovery of Stable Extra-large Pore Zeolites Based on Rational Design of Structure-directing Agents

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Zeolites are crucial industrial materials due to their stability and tunable properties, but current applications are limited by pore size (typically <12-membered ring).
• There's a significant industrial need for stable, three-dimensional (3D) zeolites with extra-large pores for heavy oil conversion and macromolecular catalysis.
• Previous attempts to synthesize extra-large pore zeolites often resulted in materials with poor stability, interrupted frameworks, or limited dimensionality.

Purpose of the Study:

• To report a decade-long effort in developing novel 3D stable extra-large pore zeolites.
• To introduce innovative structure-directing agents (SDAs) for synthesizing these advanced zeolites.
• To address the limitations of existing extra-large pore zeolites and achieve breakthroughs in their synthesis.

Main Methods:

• Systematic design and synthesis of novel structure-directing agents (SDAs), starting from semirigid imidazole salts and progressing to highly rigid benzimidazole-based and bulky cycloalkyl phosphines.
• Synthesis of new large and extra-large pore germanosilicate, high silica, and pure silica zeolites (NUD series).
• Development of tricyclohexylmethylphosphonium (TCyMP) as an SDA to synthesize the first 3D stable extra-large pore aluminosilicate zeolite (ZEO-1) and exploration of a 1D to 3D topotactic condensation mechanism for ZEO-2, ZEO-3, and ZEO-5.

Main Results:

• Successful synthesis of NUD-1/2/3 (large/extra-large pore germanosilicates) and NUD-5/6 (high silica/pure silica extra-large pore zeolites) using imidazole-based SDAs.
• Development of TCyMP-based SDA leading to the first 3D stable extra-large pore aluminosilicate zeolite, ZEO-1.
• Discovery of a novel 1D to 3D topotactic condensation mechanism, enabling the synthesis of ZEO-3 and ZEO-5, expanding the limits of 3D stable zeolite pore sizes.

Conclusions:

• The ZEO series represents a significant breakthrough, filling the gap between large-pore zeolites and mesoporous materials with 3D stable extra-large pore structures.
• The developed SDAs and synthetic strategies are crucial for advancing zeolite science and enabling selective catalysis of macromolecules.
• Continued advancements in synthesis, characterization, and machine learning are expected to drive future developments in zeolite exploration.