Zeolite and molecular sieve synthesis

Davis, Mark E.; Lobo, Raúl F.

doi:10.1021/cm00022a005

Cited by 1,382 publications

(1,089 citation statements)

References 3 publications

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“…In previous reports involving the enrichment of polymorph A in *BEA (which does not guarantee enantioenrichment), characterization of any true structural enrichment of polymorph A has been limited to transmission electron microscopy (TEM) analysis (PXRD analyses are fraught with problems) of the polymorph domains and demonstration of enantioenrichment by measuring some function (e.g., catalysis or adsorption) (15,16). A distinct issue with this methodology, however, is that the synthesis of these materials lacks proper controls with regard to the enantiomorphs obtained in the product materials, and therefore it is not possible to perform appropriate analytical and experimental controls to confirm chirality.…”

Section: Resultsmentioning

confidence: 99%

Enantiomerically enriched, polycrystalline molecular sieves

Brand

Schmidt

Deem

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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112

140

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Zeolite and zeolite-like molecular sieves are being used in a large number of applications such as adsorption and catalysis. Achievement of the long-standing goal of creating a chiral, polycrystalline molecular sieve with bulk enantioenrichment would enable these materials to perform enantioselective functions. Here, we report the synthesis of enantiomerically enriched samples of a molecular sieve. Enantiopure organic structure directing agents are designed with the assistance of computational methods and used to synthesize enantioenriched, polycrystalline molecular sieve samples of either enantiomer. Computational results correctly predicted which enantiomer is obtained, and enantiomeric enrichment is proven by high-resolution transmission electron microscopy. The enantioenriched and racemic samples of the molecular sieves are tested as adsorbents and heterogeneous catalysts. The enantioenriched molecular sieves show enantioselectivity for the ring opening reaction of epoxides and enantioselective adsorption of 2-butanol (the R enantiomer of the molecular sieve shows opposite and approximately equal enantioselectivity compared with the S enantiomer of the molecular sieve, whereas the racemic sample of the molecular sieve shows no enantioselectivity). chirality | zeolite | asymmetric catalysis | chiral adsorption

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Section: Resultsmentioning

confidence: 99%

Enantiomerically enriched, polycrystalline molecular sieves

Brand

Schmidt

Deem

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

112

140

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“…10 Considering "impossible" solids, it had long been thought that thermodynamics dictates the close packing of atoms in the lattice of crystals. However, the discovery of large families of naturally occurring and synthetic zeolites with massive internal void spaces quickly overturned that belief 11 and established that kinetic stability dominates over thermodynamic stability in these types of metastable open framework solids. 12 Over half a century of research on template-directed synthesis of zeolites had created the impression that obtaining pore sizes beyond the microporous limit of 2 nm would be impossible.…”

Section: The Utilization Of the Inherently Unstable Multiplymentioning

confidence: 99%

Periodic Mesoporous Hydridosilica − Synthesis of an “Impossible” Material and Its Thermal Transformation into Brightly Photoluminescent Periodic Mesoporous Nanocrystal Silicon-Silica Composite

et al. 2011

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There has always been a fascination with “impossible” compounds, ones that do not break any rules of chemical bonding or valence but whose structures are unstable and do not exist. This instability can usually be rationalized in terms of chemical or physical restrictions associated with valence electron shells, multiple bonding, oxidation states, catenation, and the inert pair effect. In the pursuit of these “impossible” materials, appropriate conditions have sometimes been found to overcome these instabilities and synthesize missing compounds, yet for others these tricks have yet to be uncovered and the materials remain elusive. In the scientifically and technologically important field of periodic mesoporous silicas (PMS), one such “impossible” material is periodic mesoporous hydridosilica (meso-HSiO1.5). It is the archetype of a completely interrupted silica open framework material: its pore walls are comprised of a three-connected three-dimensional network that should be so thermodynamically unstable that any mesopores present would immediately collapse upon removal of the mesopore template. In this study we show that meso-HSiO1.5 can be synthesized by template-directed self-assembly of HSi(OEt)3 under aqueous acid-catalyzed conditions and after template extraction remains stable to 300 °C. Above this temperature, bond redistribution reactions initiate a metamorphic transformation which eventually yields periodic mesoporous nanocrystalline silicon-silica, meso-ncSi/SiO2, a nanocomposite material in which brightly photoluminescent silicon nanocrystallites are embedded within a silica matrix throughout the mesostructure. The integration of the properties of silicon nanocrystallinity with silica mesoporosity provides a wealth of new opportunities for emerging nanotechnologies.

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“…36 At the conditions commonly used for silicalite-1 synthesis (high water/silicon ratio and high pH), hydrolysis of TEOS, yielding silicic acid and ethanol, is complete. 30,31 We are thus left with a system containing water, ethanol, TPA, Si(OH) 4 and OH -. To simplify this picture, we begin by ignoring the effect of ethanol and consider the water/ ethanol mixture as a single solvent species (hereafter designated by W).…”

Section: Model Descriptionmentioning

confidence: 99%

Modeling Spontaneous Formation of Precursor Nanoparticles in Clear-Solution Zeolite Synthesis

2005

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Abstract:We present a lattice model describing the formation of silica nanoparticles in the early stages of the clear-solution templated synthesis of silicalite-1 zeolite. Silica condensation/hydrolysis is modeled by a nearest-neighbor attraction, while the electrostatics are represented by an orientation-dependent, shortrange interaction. Using this simplified model, we show excellent qualitative agreement with published experimental observations. The nanoparticles are identified as a metastable state, stabilized by electrostatic interactions between the negatively charged silica surface and a layer of organic cations. Nanoparticle size is controlled mainly by the solution pH, through nanoparticle surface charge. The size and concentration of the charge-balancing cation are found to have a negligible effect on nanoparticle size. Increasing the temperature allows for further particle growth by Ostwald ripening. We suggest that this mechanism may play a role in the growth of zeolite crystals.

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Zeolite and molecular sieve synthesis

Cited by 1,382 publications

References 3 publications

Enantiomerically enriched, polycrystalline molecular sieves

Enantiomerically enriched, polycrystalline molecular sieves

Periodic Mesoporous Hydridosilica − Synthesis of an “Impossible” Material and Its Thermal Transformation into Brightly Photoluminescent Periodic Mesoporous Nanocrystal Silicon-Silica Composite

Modeling Spontaneous Formation of Precursor Nanoparticles in Clear-Solution Zeolite Synthesis

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