Micro/Mesoporous Zeolitic Composites: Recent Developments in Synthesis and Catalytic Applications

Abstract

Micro/mesoporous zeolitic composites (MZCs) represent an important class of hierarchical zeolitic materials that have attracted increasing attention in recent years. By introducing an additional mesoporous phase interconnected with the microporosity of zeolites, a hierarchical porous system of MZCs is formed which facilitates molecular transport while preserving the intrinsic catalytic properties of zeolites. Thus, these materials offer novel perspectives for catalytic applications. Over the years, numerous synthesis strategies toward the formation of MZCs have been realized and their catalytic applications have been reported. In this review, the three main synthesis routes, namely direct synthesis using zeolite precursors, recrystallization of zeolites, and zeolitization of preformed mesoporous materials are thoroughly discussed, with focus on prior works and the most recent developments along with prominent examples given from the literature. In addition, the significant improvement in the catalytic properties of MZCs in a wide range of industrially relevant reactions is presented through several representative cases. Some perspectives for the future development of MZCs are also given.

Nature and Location of Carbonaceous Species in a Composite HZSM-5 Zeolite Catalyst during the Conversion of Dimethyl Ether into Light Olefins

“…For this reason, zeolite is agglomerated within a matrix that provides the catalyst particles with the appropriate mechanical and physical properties. Furthermore, the matrix provides the microporous zeolite with an additional system of meso-and macropores [24]. Michels et al [25] highlight the importance of the zeolite agglomeration in order to use the catalyst at industrial scale, yielding a final catalyst composite with an improved mechanical resistance and a hierarchical porous texture that extends the catalyst lifetime.…”

Strategies to Enhance the Catalytic Performance of ZSM-5 Zeolite in Hydrocarbon Cracking: A Review

“…The composite zeolites not only maintained the intrinsic activity of ZSM-5 zeolite, but also showed synergistic effect with other materials. For catalytic cracking Catalysts 2017, 7, 367 5 of 31 of hydrocarbon, a second zeolite was usually introduced to increase the diffusion of molecule and the accessibility of acid sites in the micropores of ZSM-5 zeolite, thus enhancing the catalytic activity of ZSM-5 zeolite [34].…”

“…Besides, this method avoided the ion exchange with NH 4 NO 3 and calcining processes to obtain protonated zeolite compared with NaOH treatment method. the diffusion of molecule and the accessibility of acid sites in the micropores of ZSM-5 zeolite, thus enhancing the catalytic activity of ZSM-5 zeolite [34]. ZSM-5@MCM-41 composite zeolite was prepared by treating ZSM-5 zeolite with sodium hydroxide solution, and then the dissolved silica and aluminum were recrystallized on the surface of ZSM-5 zeolites in the form of MCM-41 in the presence of cetyltrimethylammonium bromide (CTAB) [23][24][25]35].…”

Catalytic Conversion of 1‐butene over Modified Versions of Commercial ZSM‐5 to Produce Clean Fuels and Chemicals

“…Thus, great focus has been put on developing improved versions of zeolites with enhanced active sites accessibility, allowing facilitated mass transfer in/out of the pores, while benefiting from zeotype features (structural order at the atomic level, tunable surface properties and shape selectivity) . This may be accomplished with the introduction of mesoporosity in zeolites via bottom‐up or top‐down synthetic approaches . In the former case, mesoporosity is formed by hard templating (e. g. carbonaceous or polymeric compounds), soft templating (e. g. surfactants, organosilanes), or indirect templating methods (e. g. steam‐assisted and solid‐phase crystallization) .…”

“…[18][19][20][21][22] This may be accomplished with the introduction of mesoporosity in zeolites via bottom-up or top-down synthetic approaches. [23][24][25][26][27][28][29] In the former case, mesoporosity is formed by hard templating (e. g. carbonaceous or polymeric compounds), [30][31][32] soft templating (e. g. surfactants, organosilanes), [33][34][35] or indirect templating methods (e. g. steam-assisted and solid-phase crystallization). [36][37][38] In top-down approaches, mesoporosity is introduced by strategically removing framework atoms from pre-made zeolites; e. g. desilication via alkaline treatment, [39][40][41][42] and dealumination via acid treatment or steaming at high temperature.…”