Tailoring Silicalite‐1 Crystal Morphology with Molecular Modifiers

Lupulescu, Alexandra I.; Rimer, Jeffrey D.

doi:10.1002/ange.201107725

Cited by 40 publications

(33 citation statements)

References 40 publications

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“…One attribute of ZGMs that has not been previously exploited is the ability to tune their charge by selecting a growth solution pH that overlaps the dissociation constants (pK a values) of functional moieties. Our prior study of silicalite-1 26 used a growth solution with pH 12.7, which is much larger than the dissociation constants of ZGMs. Here, we work with less alkaline growth solutions (pH ≤ 12) to examine the effect of ZGM charge on MFI precursor formation.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Here we assess the prenucleation stage of MFI synthesis in the presence of commercially available ZGMs that selectively tune crystal size and/or morphology. Our prior study 26 has shown that spermine (Scheme 2a) and tributylphosphine oxide (TBPO, Scheme 2d) are effective ZGMs that specifically interact with MFI {010} surfaces. D-Arginine (D-Arg, Scheme 2c) is another effective ZGM that interacts with {101} surfaces.…”

Section: ■ Introductionmentioning

confidence: 99%

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Tuning Zeolite Precursor Interactions by Switching the Valence of Polyamine Modifiers

2016

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Nonclassical mechanisms of crystal growth often involve the formation of amorphous precursors that play a direct role in what is generally referred to as crystallization by particle attachment (or CPA). One of the most studied CPA systems in the literature is zeolite MFI, which is a microporous crystal with siliceous (silicalite-1) and aluminosilicate (ZSM-5) isostructures. The self-assembly, microstructural evolution, and mechanistic role of nanoparticle precursors (1-6 nm) during silicalite-1 crystallization have been the subjects of prior investigation by combined experimental and modeling techniques. Here we investigate for the first time the effects of zeolite growth modifiers (ZGMs) on MFI precursors. ZGMs are organic molecules that alter the anisotropic rate(s) of crystal growth as a means of tailoring crystal size and/or habit. We show that most ZGMs have little effect on precursor assembly and evolution during the prenucleation stages of silicalite-1 and ZSM-5 synthesis; however, studies at varying alkalinity reveal that pH can be used as a "switch" to tune ZGM speciation and concurrently the colloidal stability of precursors. This has been proven effective for various polyamine compounds, such as spermine, that exhibit divalent (positive) charge near negatively charged nanoparticle surfaces. Our finding is consistent with colloidal models that predict a higher concentration of divalent modifiers within the diffuse double layer surrounding the surfaces of (alumino)silicate precursors. Multivalent polyamines seemingly promote precursor-precursor aggregation at elevated temperature, which is consistent with a proposed hypothesis that modifiers with two or more sufficiently spaced cationic functional moieties are capable of bridging neighboring precursor surfaces, thus overcoming an electrostatic repulsive force that contributes to their colloidal stability. Given the importance of precursor-precursor and precursor-crystal interactions in zeolite nucleation and growth, respectively, our observations provide additional insight into the role of organics in zeolite crystallization.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Tuning Zeolite Precursor Interactions by Switching the Valence of Polyamine Modifiers

2016

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“…52,53 When the attachment occurs, colloidal particles close to the little crystal must be primarily along the c-and a-axis directed by TMG, as the TMG molecules preferentially bind to the a-c face of the crystals with the MFI structure via special imino groups. [16][17][18]54 Thus, the oriented attachment of colloidal particles to the little crystal mainly along the a-and c-axis, and the subsequent epitaxial crystallization of the colloidal particles on the little crystal via the solid-phase transformation route explain well why the synthesis in the presence of TMG could produce plate-like crystals with single-crystalline nature but hierarchical structure. The corresponding mechanism is schematically illustrated in Fig.…”

Section: Formation Mechanism Of Plate-like Crystals With Singlecrysta...mentioning

confidence: 99%

“…[12][13][14][15] (3) Preparing thin lamellar crystals in the b-axis direction to shorten the primary diffusion path of the mass transfer within zeolite crystals. [16][17][18] For the ZSM-5 zeolite catalyst with nano-size crystallites, although the diffusion limitation problem could be solved well as expected, it still suffers from low thermal stability. 19 To obtain the ZSM-5 zeolite with hierarchical structure, two general strategies, so-called top-down and bottom-up routes, have been respectively developed.…”

Section: Introductionmentioning

confidence: 96%

Constructing single-crystalline hierarchical plate-like ZSM-5 zeolites with short b-axis length for catalyzing MTO reactions

Shang

Chen

Zhang

et al. 2022

Inorg. Chem. Front.

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“…The use of additives can also effectively tailor the aspect ratio of zeolite crystals. Different types of additives, including alcohol, 38,39 tributylphosphine oxide, 40 graphene oxide, 41 peptoids, 42 and amino acid arginine, 43 were employed to modify crystal morphology of different types of zeolites. Although some positive results were published, a dramatic change in the aspect ratio between different faces was not reported to the best of our knowledge.…”

Section: Introductionmentioning

confidence: 99%

Platelike MFI Crystals with Controlled Crystal Faces Aspect Ratio

et al. 2021

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Zeolite crystals offering a short diffusion pathway through the pore network are highly desired for a number of catalytic and molecule separation applications. Herein, we develop a simple synthetic strategy toward reducing the thickness along b-axis of MFI-type crystals, thus providing a short diffusion path along the straight channel. Our approach combines preliminary aging and a fluoride-assisted low-temperature crystallization. The synthesized MFI crystals are in the micron-size range along a-and c-axis, while the thickness along the b-axis is a few tens of nanometers. The synthesis parameters controlling the formation of plate-like zeolite are studied, and the factors controlling the zeolite growth identified. The synthesis strategy works equally well with all-silica MFI (silicalite-1) and its Al-and Ga-containing derivatives. The catalytic activity of plate-like ZSM-5 in the methanol-to-hydrocarbons (MTH) reaction is compared with a commercial nano-sized ZSM-5 sample, as the plate-like ZSM-5 exhibits a substantially extended lifetime. The synthesis of plate-like MFI crystals is successfully scaled up to a kilogram scale.

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Tailoring Silicalite‐1 Crystal Morphology with Molecular Modifiers

Cited by 40 publications

References 40 publications

Tuning Zeolite Precursor Interactions by Switching the Valence of Polyamine Modifiers

Tuning Zeolite Precursor Interactions by Switching the Valence of Polyamine Modifiers

Constructing single-crystalline hierarchical plate-like ZSM-5 zeolites with short b-axis length for catalyzing MTO reactions

Platelike MFI Crystals with Controlled Crystal Faces Aspect Ratio

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