Organic Mesopore Generating Agents (OMeGAs) for Hierarchical Zeolites: Combining Functions on Multiple Scales

Abstract

In the synthesis of porous zeolites, small organic molecules usually function as organic structure‐directing agents (OSDAs) or zeolite growth modifiers (ZGMs), while mesoporous zeolites are typically synthesized by employing the physical space‐filling strategy with mesoscale templates including carbons, surfactants, and polymers. Recently, we discovered that a class of small organic molecules including the common amino acids could mediate the formation of zeolite mesopores based on a chemical bond‐breaking mechanism. This class of organic mesopore generating agents (OMeGAs) are distinguished by their ability to form organic anions in situ. In this minireview, we briefly introduce the widely recognized role of OSDA and ZGM, and then focus on the interesting function of OMeGA for the intracrystalline void generation. Comparison of OMeGA with the mesoscale templates especially surfactants are made in terms of their mesopore‐forming mechanisms, and the potential implications on a possible dissociative‐associative crystallization pathway are discussed. We end this review with the prospects of future research on the small molecule OMeGA, such as function integration and structure optimization.

Crystallization of zeolite Beta in the presence of an anionic surfactant AESA

“…24 The roles of organic molecules in zeolite synthesis could be classified as structure directing agents, mesopore generating agents, and zeolite growth modifiers. 25 So far, the organic molecules used in zeolite synthesis have been mostly positively charged, including cationic polymers and surfactants, since positively charged groups such as ammonium and amine groups could balance the negative charge in the zeolite framework. [26][27][28][29] Cationic surfactants, such as cetyltrimethylammonium bromide (CTAB), have been applied in the synthesis of hierarchical zeolites with a high external surface area.…”