Tailoring Silicalite‐1 Crystal Morphology with Molecular Modifiers

Lupulescu, Alexandra I.; Rimer, Jeffrey D.

doi:10.1002/anie.201107725

Cited by 94 publications

(113 citation statements)

References 40 publications

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“…8 Examples include (but are not limited to) the crystallization of metal oxides, [9][10][11][12] chalcogenides 13 , calcium minerals, 14 and zeolites. 15 Zeolites are an exemplary class of materials that form via a combination of nonclassical and classical growth mechanisms. These aluminosilicate microporous materials exhibit tunable acidity, pore size/topology, and shape-selectivity for applications spanning catalysis, 16,17 photonics, 18,19 drug delivery, 20 separations, 21 and ion exchange.…”

Section: Introductionmentioning

confidence: 99%

Nucleation of FAU and LTA Zeolites from Heterogeneous Aluminosilicate Precursors

et al. 2016

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The nucleation of many natural, biogenic, and synthetic crystals involves the initial formation of metastable precursors that provides a kinetic pathway for an amorphous-to-crystalline transformation. This nonclassical mechanism is believed to be the dominant crystallization pathway for microporous zeolites. Despite significant research on zeolite growth mechanisms, molecular level details regarding the assembly, physicochemical properties, and structural evolution of amorphous (alumino)silicate precursors remain elusive. Here we use a combination of diffraction, scattering, and microscopy techniques to characterize the amorphous precursors that assemble and evolve during the synthesis of zeolites FAU and LTA -two materials that are widely used in commercial applications such as catalysis, adsorption, separations, and ion-exchange. Nucleation occurs by a two-step mechanism involving the initial formation of aggregates that serve as heterogeneous sites for nucleation. Using colloidal silica as a reagent, we observe that precursors are comprised of heterogeneous silica and alumina domains due in part to the negligible dissolution of silica during room temperature aging. This indicates substantial Si-O-Si bond breakage must occur during hydrothermal treatment with concomitant exchange of soluble alumina species to achieve a final crystalline product with Si/Al ratio = 1.0 -2.5. All syntheses were performed with molar compositions of Si/Al ≥ 2.0, which favors the formation of FAU; however, we observe that certain growth conditions are capable of creating a "false" environment (i.e., Al-rich regions) that favors LTA nucleation, followed by intercrystalline transformation to FAU. Time-resolved ex situ transmission electron microscopy of extracted solids during zeolite crystallization indicates that nucleation occurs on the exterior surface of precursors. This observation is consistent with our proposed hypothesis that posits exterior surfaces are more energetically favorable sites for nucleation compared to the particle interior on the basis of confinement effects. Given that numerous zeolite syntheses involve the initial formation of metastable precursors with heterogeneous composition, the pathway for nucleation proposed in this study may prove to be generalizable to other zeolite structures and related materials.

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Section: Introductionmentioning

confidence: 99%

Nucleation of FAU and LTA Zeolites from Heterogeneous Aluminosilicate Precursors

et al. 2016

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“…6 The structure of nanoblocks determine the properties of zeolite crystals. 8 Morphology control and orient growth of zeolite can be tailored by using zeolite growth modifiers, which are molecules with a specificity for binding to select crystal faces and altering the anisotropic rates of surface 40 step growth. Channels oriented 30 axially along the longest crystal dimensions, which limit molecule access to pores on exterior crystal surfaces and increase the internal path length.…”

Section: Introductionmentioning

confidence: 99%

“…7 Zeolites tend to form anisotropic crystals with pore mouth presented on low surface area faces. 8,9 Recently, extensive efforts have been devoted to the self−assembly of nanoparticles (NPs) into highly ordered architectures or super−structures because of their importance in basic research and potential applications. These factors impose severe mass transport limitations that reduce molecular flux and decrease the yield, selectivity, as well as lifetime of zeolite catalysts.…”

Section: Introductionmentioning

confidence: 99%

Hollow TS-1 mesocrystals: hydrothermal construction and high catalytic performances in cyclohexanone ammoximation

et al. 2015

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In this article, solid and hollow TS-1 mesocrystals (HTMs) with hierarchical porous structure were constructed through assembling TS-1 nanocrystalline block in hydrothermal post-treatment. TS-1 nanocrystalline blocks including organic template reagent provided solid TS-1 mesocrystals. Preremoval of template offered HTMs. In cyclohexanone ammoximation, the catalytic activity of HTMs depended 10 significantly on their hollow mesocrystalline structure. Compared to solid TS-1 mesocrystals, HTMs showed excellent catalytic performance with cyclohexanone conversion and oxime selectivity up to 100%. The hollow mesocrystalline structures of TS-1 contribute to their high surface area, hierarchical porous, robust structure and corresponding catalytic performances.

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“…[16] We proposed am echanism of steric hindrance wherein TBPO preferentially adsorbs on (010) surfaces and impedes the attachment of TPA-nanoparticles.T his is consistent with in situ AFM ( Figure S11) showing areduction in the root mean square (RMS) roughness of silicalite-1 (010) surfaces in the presence of TBPO ( Figure 4A). [16] We proposed am echanism of steric hindrance wherein TBPO preferentially adsorbs on (010) surfaces and impedes the attachment of TPA-nanoparticles.T his is consistent with in situ AFM ( Figure S11) showing areduction in the root mean square (RMS) roughness of silicalite-1 (010) surfaces in the presence of TBPO ( Figure 4A).…”

Section: Angewandte Chemiementioning

confidence: 99%

“…[16] Them ost common TAAc ation employed in silicalite-1 (MFI) synthesis is tetrapropylammonium (TPA), which functions as an OSDA. [16] Them ost common TAAc ation employed in silicalite-1 (MFI) synthesis is tetrapropylammonium (TPA), which functions as an OSDA.…”

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Regulating Nonclassical Pathways of Silicalite‐1 Crystallization through Controlled Evolution of Amorphous Precursors

2019

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Differentiating mechanisms of zeolite crystallization is challenging owingt ot he vast number of species in growth solutions.T he presence of amorphous colloidal particles is ubiquitous in many zeolite syntheses,a nd has led to extensive efforts to understand the driving force(s) for their self-assembly and putative roles in processes of nucleation and growth. In this study,w eu se ac ombination of in situ scanning probe microscopy, particle dissolution measurements,a nd colloidal stability assays to elucidate the degree to whichs ilica nanoparticles evolve in their structure during the early stages of silicalite-1 synthesis.W es how how changes in precursor structure are mediated by the presence of organics,a nd demonstrate howt hese changes lead to significant differences in precursor-crystal interactions that alter preferred modes of crystal growth. Our findings provide guidelines for selectively controlling silicalite-1 growth by particle attachment or monomer addition, thus allowing for the manipulation of anisotropic rates of crystallization. In doing so,wealso address al ongstanding question regarding what factors are at our disposal to switch from anonclassical to classical mechanism.

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Tailoring Silicalite‐1 Crystal Morphology with Molecular Modifiers

Cited by 94 publications

References 40 publications

Nucleation of FAU and LTA Zeolites from Heterogeneous Aluminosilicate Precursors

Nucleation of FAU and LTA Zeolites from Heterogeneous Aluminosilicate Precursors

Hollow TS-1 mesocrystals: hydrothermal construction and high catalytic performances in cyclohexanone ammoximation

Regulating Nonclassical Pathways of Silicalite‐1 Crystallization through Controlled Evolution of Amorphous Precursors

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