Mesostructured zeolites: bridging the gap between zeolites and MCM-41

Abstract

Surfactant-templating is one of the most versatile and useful techniques to implement mesoporous systems into solid materials. Various strategies based on various interactions between surfactants and solid precursors have been explored to produce new structures. Zeolites are invaluable as size-and shape-selective solid acid catalysts. Nevertheless, their micropores impose limitations on the mass transport of bulky feed and/or product molecules. Many studies have attempted to address this by utilizing surfactant-assisting technology to alleviate the diffusion constraints. However, most efforts have failed due to micro/ mesopore phase separation. Recently, a new technique combining the uses of cationic surfactants and mild basic solutions was introduced to synthesise mesostructured zeolites. These materials sustain the unique characteristics of zeolites (i.e., strong acidity, crystallinity, microporosity, and hydrothermal stability), including tunable mesopore sizes and degrees of mesoporosity. The mesostructured zeolites are now commercially available through Rive Technology, and show superior performance in VGO cracking. This feature article provides an overview of recent explorations in the introduction of mesoporosity into zeolites using surfactant-templating techniques. Various porous materials, preparation methods, physical and catalytic properties of mesostructured zeolites will be discussed.

Building Zeolites from Precrystallized Units: Nanoscale Architecture

“…[87] One of the preferred synthesis routes to generate the mesoporosity within crystalline zeolites is based on the post-synthetic dealumination and/or desilication with an acid or ab ase,w hich creates mesopores by extracting atoms from the zeolite framework. [87] One of the preferred synthesis routes to generate the mesoporosity within crystalline zeolites is based on the post-synthetic dealumination and/or desilication with an acid or ab ase,w hich creates mesopores by extracting atoms from the zeolite framework.…”

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

“…This frequency indicates that aluminium is incorporated into the ZMS-5 structure [29], which is confirmed for sample T12 by its 27 Al MAS NMR spectrum (not shown). On the other hand in the FTIR spectra of samples Wy (not shown) the band at 547 cm À1 is only To avoid the phase separation and the destruction of mesoporous walls during the zeolite crystallization, the steam assisted crystallization (SAC) method was employed [78][79][80][81][82][83][84].…”

“…In recent years, there has been a rapid development in synthesis and applications of hierarchical zeolitic materials. Many excellent reviews highlighting various aspects of the latest progress in this field have been published [6,[8][9][10]13,14,[16][17][18][19][20][21][22][23][24][25][26][27][28][29]. It should be noted that most of them have focused on hierarchical zeolites (HZs).…”

Mesoporous Y zeolite through ionic liquid based surfactant templating

“…This would suggest that the MPy þ cation is less prone to form ordered micelles after cation exchange and thus leading to a less defined porosity after calcination. These results thus strongly suggest that the described surfactant templating approach relies more on a truly zeolite rearrangement process as stipulated by the group of GarciaMartinez [40,41], and less on a dissolution-recrystallization process. Notwithstanding, further insights are necessary to determine the exact nature for the different templating behavior of these structural directing agents when used in surfactant templating of zeolites.…”

“…An alternative strategy is the surfactant templating approach, which allows to impart tailored mesoporosity within given zeolite structures. Different theories exist to explain the fundamental mechanism of the surfactant templating process, that are either based on zeolite recrystallization [36e39] or rearrangement [40,41]. The recrystallization mechanism is believed to rely on a preliminary partial destruction and dissolution of the zeolite framework under basic conditions followed by the re-assembly in the presence of surfactants.…”