Zeolites, a class of microporous crystalline materials, have been widely used in industry to separate gas mixtures and catalyze reactions. The properties of a given zeolite depend mainly on its crystallographic structure and the location of active sites. Recently, the development of three-dimensional electron diffraction (3D-ED) techniques enabled the solving of several complex zeolites’ structures, which helped on the understanding of structure-function relationships. However, a certain number of zeolites also possessed non-periodic local structural features (also called defects), such as grain boundaries, stacking disorders, and point/line defects, which also have important effects on their performance.
Herein, for the first part, we showed structure determination of several zeolites using electron microscopy, especially the combination of 3D ED technique and high-resolution electron microscopic images ( Figure 1). To be specific, we showed the structure determination of a polymorph E-enriched beta zeolite. And we discussed the structure-function relationships of ECNU-27 [ 1] and ECNU-28 [ 2] zeolite to elucidate the importance of structure determination for materials. Moreover, some special cases like layer deflection from ECNU-34 zeolite and ‘edge dislocation-like’ intergrowth from ECNU-35 zeolite are shown as well.
A conclusion could be drawn from these works that the defects in zeolite would affect its application performance. Therefore, in the second part, we want to show how we utilizing the defects in zeolite (silanols) to solve a challenging gas separation problem in industrial application ( Figure 2) [ 3]. The very small differences of boiling points and molecular sizes between cyclohexane and benzene makes the separation process challenging. We achieved the efficient production of ultrapure cyclohexane (benzene < 1 ppm) from benzene/cyclohexane mixture under dynamic condition with an -SVR zeolite by the synergy of pore size and ordered silanols inside zeolite. [4]
Fig. 1.
Defects in zeolites unraveled by high-resolution electron microscopy.
Fig. 2.
Synergy of pore size and silanols in zeolite for benzene/cyclohexane separation.
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