A Comprehensive Review of the Applications of Hierarchical Zeolite Nanosheets and Nanoparticle Assemblies in Light Olefin Production

Abstract

Light olefins including ethylene, propylene and butylene are important building blocks in petrochemical industries to produce various chemicals such as polyethylene, polypropylene, ethylene oxide and cumene. Traditionally, light olefins are produced via a steam cracking process operated at an extremely high temperature. The catalytic conversion, in which zeolites have been widely used, is an alternative pathway using a lower temperature. However, conventional zeolites, composed of a pure microporous structure, restrict the diffusion of large molecules into the framework, resulting in coke formation and further side reactions. To overcome these problems, hierarchical zeolites composed of additional mesoporous and/or macroporous structures have been widely researched over the past decade. In this review, the recent development of hierarchical zeolite nanosheets and nanoparticle assemblies together with opening up their applications in various light olefin productions such as catalytic cracking, ethanol dehydration to ethylene, methanol to olefins (MTO) and other reactions will be presented.Catalysts 2020, 10, 245 2 of 15 windows, they can be divided into three different categories including large porous, medium porous and small porous zeolites, which are composed of a different number of tetrahedral units, or T atoms of 12, 10 and 8 membered rings, respectively. These behaviors make each zeolite serving unique shape selective properties, which are very important for the appropriate applications.Although there are several above-mentioned promising properties of zeolites, they are typically composed of a very small microporous structure, eventually resulting in some disadvantages of the diffusion limitation of guest molecules inside the framework. Some bulky molecules cannot easily penetrate into active sites located at microporous channels, and therefore a poor catalytic performance due to a very low reaction rate and a fast deactivation of catalysts is observed. To overcome these limitations and to improve the accessibility of molecules into active sites, in recent years modified zeolites obtained by introducing additional larger porous structures have been extensively developed [5][6][7][8].It is well known that hierarchical zeolites, composed of at least two levels of porous structures such as microspores and mesopores, microspores and macropores, and micropores/mesopores and macropores have been extensively studied and developed. Their microporous (<2 nm), mesoporous (2-50 nm) and/or macroporous (>50 nm) structures are well connected to each other. In this case, the additional larger porous structures can improve diffusion limitation, molecular transportation and coke deposition [9]. In the past decade, there have been several studies regarding the synthesis of hierarchical zeolites to overcome these problems. Herein, this comprehensive review opens up perspectives of the recent synthesis approaches of hierarchical zeolite nanosheets and nanoparticle assemblies, as well as the successful production of light olef...

Advanced Ordered Nanoporous Materials

“…Zeolite topologies in 2D structures are considered primary structures, while the various layered forms can be denoted as secondary structures (Roth et al 2014a), with layers of one-unit cell or smaller thickness structures. The first synthesis of MFI zeolite nanosheets was approached using quaternary ammonium surfactant, C 22 H 45 -N + (CH 3 ) 2 -C 6 H 12 -N + (CH 3 ) 2 -C 6 H 13 (C 22-6-6 ) as a structure-directing agent (SDA), which can be used to control microporous structures and nanolayer features (Dugkhuntod and Wattanakit 2020). More details in the synthesis of 2D zeolites are explained later.…”

Robust CON-type zeolite nanocatalyst in methanol-to-olefins reaction: downsizing, recrystallisation and defect-healing treatments toward prolonged lifetime

“…The methanol-to-olefins (MTO) reaction is a key technology for providing light olefins, important building blocks for various chemicals, from non-oil resources. [1][2][3] The MTO catalysts with excellent stability and product selectivity are in high demand, and especially selective production of C 3 -C 4 species among light olefins is of great interest. [4][5][6][7] Zeolites and related materials are well-known catalysts that possess shape selectivity toward light olefins owing to their small pores in microporous frameworks.…”

Conversion of Methanol to Olefins over Modified OSDA-Free CHA Zeolite Catalyst

“…17,18 CHA is a small-pore zeolite with an aperture of 3.8 Å and large ellipsoidal cavities with 8.35 Å. 19 CHA can be obtained from nature or be synthesized in the laboratory. 20 The naturally occurring CHA is of less importance in catalysis due to the large amount of impurities existing in its structure.…”

“…The most efficient zeolites used in the MTO are ZSM-5 (MFI type: consisting of channel intersections and crossed 10-member ring channels) and chabazite (CHA) (SSZ-13 and SAPO-34). , CHA is a small-pore zeolite with an aperture of 3.8 Å and large ellipsoidal cavities with 8.35 Å . CHA can be obtained from nature or be synthesized in the laboratory .…”