Tailored crystalline microporous materials by post-synthesis modification

Abstract

Crystalline microporous solids are an important class of inorganic materials with uses in different areas impacting our everyday lives, namely as catalysts, adsorbents, and ion exchangers. Advancements in synthesis have been invaluable in expanding the classical aluminosilicate zeolites to new unique framework types and compositions, motivating innovative developments. However, the inexhaustible post-synthetic options to tailor zeolite properties have been and will continue to be indispensable to realize emerging and to improve conventional applications. Starting from the routine drying and template removal processes that every zeolite must experience prior to use, a wide spectrum of treatments exists to alter individual or collective characteristics of these materials for optimal performance. This review documents the toolbox of post-synthetic strategies available to tune the properties of zeolitic materials for specific functions. The categorisation is based on the scale at which the alteration is aimed at, including the atomic structure (e.g. the introduction, dislodgment, or replacement of framework atoms), the micropore level (e.g. template removal and functionalisation by inorganic and organic species), and the crystal and particle levels (e.g. the introduction of auxiliary porosity). Through examples in the recent literature, it is shown that the combination of post-synthetic methods enables rational zeolite design, extending the characteristics of these materials way beyond those imposed by the synthesis conditions.

π–π interaction of aromatic groups in amphiphilic molecules directing for single-crystalline mesostructured zeolite nanosheets

“…Synthesis of BC Ph-n-6-6 (4)(5)(6)(7)(8). The detailed synthesis procedures were illustrated in Supplementary Fig.…”

“…There are several methods to prepare hierarchical zeolites such as top-down desilication by alkali post-synthetic modification 5 , bottom-up directed assembly by self-assembly of various zeolite seeds 6 and by templates. Much attention has been focused on the synthesis of zeolites with desired pore structure using soft and hard templates, such as surfactants [7][8][9] , cationic polymer 10 , polystyrene beads 11 , mesoporous silica 12 and carbon materials [13][14][15] .…”

Catalytic test reactions for the evaluation of hierarchical zeolites

“…Furthermore, the new methods should be simple, cheap and applicable to different zeolite structures. 6,12 Another trend is to develop methods which can be used to prepare hierarchical zeolites with a wide range of Si/Al ratios. Last but not least, new methods should be able to prepare hierarchical zeolites with high zeolitic character.…”

Mesoporous MEL, BEA, and FAU zeolite crystals obtained by in situ formation of carbon template over metal nanoparticles

“…Furthermore, zeolites possess high surface areas and large pore volumes and are therefore used in many modern industrial processes related to catalysis, adsorption, and separation, where they provide excellent sizeand shape-selectivity [3,4]. However, the large-scale application of zeolites has still not reached its full potential [5], because zeolite catalysts often suffer from severe diffusion limitations.…”

“…Moreover, in some reactions, coke formation enhances these limitations, as the coke deposits block the zeolite micropores, which results in a rapid decrease in catalytic activity [6,7]. Therefore, several preparative strategies have been developed in the attempt to improve the performance of zeolites in catalysis: the synthesis of zeolites with extra-large pores [8][9][10][11], direct synthesis of zeolite nanocrystals [12][13][14][15][16][17], by exfoliating layered zeolites [18,19], and by introducing mesopores in the microporous materials through templating strategies [7, 20 -22] or demetallation processes [4,7,[23][24][25]. Recently, a novel synthesis procedure for the preparation of mesoporous MFI-type material based on the carbon templating method with an in-situ-generated carbon template was reported by our group [26].…”