Tailoring the Morphology of MTW Zeolite Mesocrystals: Intertwined Classical/Nonclassical Crystallization

Abstract

The morphology and porosity of zeolite play a significant role in the activity and selectivity of catalytic reactions. It is a dream to optionally modulate zeolite morphology by regulating the crystallization process on the basis of comprehensively understanding the mechanisms. Herein, a series of MTW zeolite mesocrystals can be consciously fabricated with morphologies from a dense structure to a loose one of an oriented nanocrystallite aggregate by changing the H 2 O/SiO 2 ratio. Their intertwined classical/nonclassical crystallization processes are investigated comprehensively. The results indicate that the crystallization of MTW zeolite takes place by a chain of events, including the formation of wormlike particles (WLPs), their aggregation, and crystallization of aggregates. MTW with a loose structure mainly crystallizes by an internal reorganization after a fast aggregation of WLPs in a concentrated system. On the other hand, the dense structure of MTW is realized via the co-occurrence of a coalescence of the participating WLPs during its crystal growth with a slower rate in a dilute system. Moreover, the advantages of MTW with a loose structure are confirmed through cumene cracking and 1,2,4trimethylbenzene transformation. This method could pave the way for the synthesis of other zeolites with diverse morphologies and/or mesoporosities via subtle regulation of the crystallization pathway.

A Solvent‐dependent Fluorogenic Probe Containing Julolidine for Cr(III) and Cu(II)

“…Based on the UV-vis titration results, the association constant (K a ) was calculated to be K a = 9.0 × 10 3 M −1 by the Benesi-Hildebrand equation (Figure S3), which is similar to those reported with other chemosensors for Cr 3+ . 6,7 This result suggests that EW1 binds strongly with Cr 3+ . The binding mode of EW1 with Cr 3+ was further examined by 1 H NMR titrations ( Figure S4).…”

“…Some organic chemosensors for Cr 3+ have been reported based on turn-on emission sensing. [5][6][7] Recently some selective probes for trivalent metal ions, including Al 3+ , Cr 3+ , and Fe…”

Unraveling the Twin and Tunability of the Crystal Domain Sizes in the Medium‐Pore Zeolite ZSM‐57 by Electron Crystallography

“…A small amount of ZSM‐57‐Na‐Inter with a smooth surface and around 200 nm in size starts to appear (as verified by PXRD and SEM, Figure a, 18 h) in this system. After 36 h of heating, the individual particles seem to merge and cross‐link together to form amorphous worm‐like particles (WLPs, Figure a, 36 h and Figure S7), which have been recognized as typical precursors in the heterogeneous medium of zeolite synthesis, for example, CHA ‐, MFI ‐, MTW ‐, TON ‐, LTL ‐, and GIS ‐type zeolites. In the sample after 54 h of heating, initial pentagonal nanoplates with a smooth surface (ca.…”

“…Besides determining novel structures through electron crystallography, TEM is also one of the effective approaches used to probe the mechanism of zeolite growth. During the crystallization of zeolites, two concerted pathways have been identified: 1) Soluble molecules accrete on the crystal surface (classical) and 2) amorphous nanoparticles attach to the crystal surface (nonclassical) . Crystal growth by the classical layer‐by‐layer mechanism exhibits a well‐defined crystal habit, whereas the nonclassical mechanism involving attachment and subsequent rearrangement of amorphous precursors leads to an irregular morphology with a lack of distinct facets and/or rough surface features composed of protrusions with sizes equivalent to the precursors .…”

“…Crystal growth by the classical layer‐by‐layer mechanism exhibits a well‐defined crystal habit, whereas the nonclassical mechanism involving attachment and subsequent rearrangement of amorphous precursors leads to an irregular morphology with a lack of distinct facets and/or rough surface features composed of protrusions with sizes equivalent to the precursors . The imaging and diffraction obtained from TEM can be employed to check the particle size of distinct populations and the spatial distribution of regions of interest, discriminate the amorphous and crystalline regions, analyze the crystallographic orientation of crystals, etc. during the crystallization process.…”