Abstract:
Zeolites are a group of crystalline (alumino)silicates connected by TO4 (T = Si or Al) tetrahedrons through corner-sharing oxygen atoms. These crystals possess welldefined micropores and channels, extra-framework cations, and Brønsted acid sites, making them promise for adsorption, separation, ion exchange, and catalysis. So far, over 250 topologies of zeolites have been synthesized, and they are widely applied in the industry, especially for energy and biomedical applications. However, the crystallization of zeolites is not well-understood yet, as it involves a complicated disorder-to-order transformation of the aluminosilicate species under hydrothermal conditions. In particular, the emergence of zeolitic structural building units inside an amorphous aluminosilicate matrix is difficult to monitor due to diverse luminosilicate ring structures and the large amorphous particles (ca. 1 – 10 μm) formed during zeolite synthesis. As a result, the development of efficient methods for controlling the zeolite crystallization kinetics is significantly hindered. In this talk, I will first overview the crystallization behaviors of zeolites in representative systems, distinguished by different sizes of the aluminosilicate particles. Then, I will introduce the formation pathway of structural building units during the crystallization of zeolite X (FAU-type), resolved by an array of characterization techniques, including synchrotron X-ray total-scattering experiments and Raman spectroscopy. Furthermore, I will show the autocatalytic nucleation behavior of mordenite (MOR-type) from amorphous particles with sizes as large as 12 μm, revealed by an “intermediate stirring” synthesis method. These studies suggest that the crystallization of zeolites can be controlled by the reaction kinetics of source ingredients and the effective solid-liquid interface of the amorphous particles. Finally, based on the findings covered in this talk, the future prospective of zeolite synthesis will be suggested.