TWO DIMENSIONAL (2D) LEWIS ACIDIC ZEOLITE NANOSHEETS: SYNTHESIS, CHARACTERIZATION AND APPLICATIONS IN CATALYSIS AND SEPARATION

Abstract

Zeolites are generally defined as 3D crystalline microporous aluminosilicates, widely used for adsorption, separation, and acid catalysis in chemical and petrochemical industry. Except for aluminum, other elements, such as B, Ti and Sn, also can be incorporated into zeolite frameworks, bringing different Lewis acidities and conferring various chemical properties. Although the zeolites are eco-friendly industrial-scale catalysts, they are challenged in the catalytic processes involving bulky molecules. The inaccessibility of active sites confined in zeolite micropores and slow mass transport lead to inferior catalytic performances. In comparison to 3D zeolite, 2D zeolites, which are endowed intrinsic properties of micropores and enhanced mass transport as well as active site accessibility of mesopores, have gained enormous attention owing to their improved performance.

This dissertation introduces several methods to prepare 2D zeolites and explores their applications in catalysis and separation. Firstly, we reported a low-cost method to prepare long-range ordering multilamellar titanium silicalite-1 (TS-1) zeolite. The pillarization on multilamellar TS-1 zeolite has been achieved to preserve the mesoporosity, while the influences of several synthesis parameters have been investigated to optimize the synthesis conditions. Afterwards, aiming to advance the understanding of Lewis acidity in these 2D TS-1 zeolites, we quantitatively described the concentration, strength and local environment of these Lewis acid sites, and evaluated their kinetic behaviors. Besides, a bottom-up method and a top-down method were introduced to prepare delaminated 2D zeolite nanosheets. With the assistance of a special-designed structure-directing agent, several heteroatom-containing 2D zeolite nanosheets have been directly synthesized. Their structural and textural properties have been evaluated by various techniques. In the top-down method, starting from multilamellar silicalite-1 (S-1) zeolites via exfoliation and separation steps, the delaminated S-1 zeolite nanosheets can be obtained and used to fabricate ultra-thin zeolite membrane applied in ethanol/water pervaporation. At last, we have created a series of novel ultra-thin film photocatalytic light absorbers (UFPLAs) to solve the long-standing trade-off between optical absorption and carrier transportation in photocatalyst. The UFPLAs have significantly boosted the activities in photocatalysis, in comparison to the benchmark Aeroxide®P25 catalyst, such as photocatalytic carbon dioxide reduction and photocatalytic chemical war agent simulant detoxification.