Introduction

Zeolite is a crystalline inorganic porous material with regular micropores, rich acid/basic sites and extraordinarily robust structures. Among the porous materials, zeolite is the most widely applied in industrial organic synthesis associated with petrochemistry, oil refining, and fine and special chemicals production. The structural advantage (such as a well-defined channel system and large surface area) of zeolite is conducive to its application in hydrogenation reactions. Furthermore, as a catalyst, its surface acid/basic sites directly act as catalytic active sites; as catalyst support, zeolite can improve the catalytic activity by influencing the electronic properties of catalysts.

Advantage

Zeolite is a crystalline nanoporous inorganic material whose structure is formed by TO4 tetrahedrons (T = Si, Al, P, etc.). These tetrahedrons are connected by corner-sharing oxygen atoms to form a 3D framework with a well-defined channel or cavity. The restricted void space within the crystal allows the zeolite to discriminate molecules based on size and/or shape differences. Furthermore, zeolite has a large surface area, a regular microporous structure, high ion exchange ability, and strong acidity. Zeolite has been widely used in various fields, such as catalysis, adsorption, environment and biomedicine. The excellent catalytic performance of zeolite arises largely from its structure and composition characteristics, such as accessible void space, open pore size, Si/Al atomic ratio, channel size and location of cations[1].

Zeolite nanocrystals

Zeolite nanocrystals are believed to have advantages over zeolite microparticles in that they have larger external surface areas, shorter diffusion path lengths ,and lower tendencies to form coke. The improved properties of the zeolite nanocrystals could possibly lead to promising applications as catalysts, in environmental protection, as chemical sensors , and in electronic applications For example, polymer-zeolite nanocomposite membranes may be used in air separation and water purification.

Zeolite composites

Zeolite composites, composed of two or more types of zeolite materials, can thus combine the different pore structures at the nanoscale and lead to the synergy between the acid sites of different zeolites. These features endow zeolite composites with unique performances in catalysis, adsorption and separation. For example, in the hydrocracking of vacuum gas oil, Y-Beta zeolite composites showed higher activity and middle distillate yield than the corresponding physical mixture of Y and Beta zeolites. Another example is the application of betaesilicalite-1 composite material in adsorption and separation. The composite material allowed more selective separation of mono- and di-branched hexane isomers than either of its components alone and had a significantly higher adsorption capacity than silicalite-1. Therefore, a great and intense interest in zeolite composites has been expressed[2].

References

[1] Xiaojun Zeng . “Microwave synthesis of zeolites and their related applications.” Microporous and Mesoporous Materials 323 (2021): Article 111262.

[2] Meng Pan . “Zeolite-zeolite composite composed of Y zeolite and single-crystal-like ZSM-5 zeolite: Fabricated by a process like ‘big fish swallowing little one.’” Materials Chemistry and Physics 194 (2017): Pages 49-54.