Analysis of the crystal growth mechanism of TPA-silicalite-1

Schoeman, Brian J.; Sterte, Johan; Otterstedt, Jan-Erik

doi:10.1016/0144-2449(94)90192-9

Cited by 120 publications

(111 citation statements)

References 14 publications

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“…When comparing growth rates, one has to keep in mind that these are strongly dependent on factors like the chemical composition of the synthesis mixture, the temperature, aging histories, and agitation or stirring. Therefore, even when taking into account the differences in reaction temperature by an Arrhenius relationship with an activation energy for crystal growth of 50 kJ/mol (approximate average of values reported in literature 44,14 ), faster 45 as well as slower 15 growth rates can be found. In agreement with light scattering results of Persson et al 15 we found the growth rate to be about the same for synthesis mixtures of varying alkalinity.…”

Section: Saxs/waxs and Usaxs Resultsmentioning

confidence: 99%

“…14,15 A disadvantage of visible light scattering for our system is that it cannot be used for turbid samples, and, in the case of an aggregating system, the size of the individual particles cannot be determined. Therefore it can only be used ex situ at advanced stages of the crystallization process by diluting the samples and cannot be used for samples in which a heterogeneous gel phase is formed.…”

Section: Introductionmentioning

confidence: 99%

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In Situ Investigation of Si-TPA-MFI Crystallization Using (Ultra-) Small- and Wide-Angle X-ray Scattering

et al. 1997

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The formation of precursors and the growth and aggregation of silicalite-1 crystals using tetrapropylammonium as a template (Si-TPA-MFI) has been studied in situ using X-ray scattering techniques. Simultaneous smallangle and wide-angle X-ray scattering (respectively SAXS and WAXS) experiments using synchrotron light showed that the formation of amorphous colloidal aggregates in water clear synthesis mixtures was dependent on the alkalinity of the solutions. In situ time-resolved ultra-small-angle X-ray scattering (USAXS) showed the form factor oscillations of the growing crystals. Fitting of the USAXS patterns to the scattering pattern of spherical particles having a normal particle size distribution showed a linear growth of the average crystal diameter, which was approximately the same for both alkalinities studied. The final size of the crystals was highest for the synthesis mixture having the highest alkalinity, which can be explained in terms of number of viable nuclei formed. At the end of the linear growth the crystals form aggregates corresponding with a diffusion limited aggregation process (mass fractal dimension of 1.8).

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Section: Saxs/waxs and Usaxs Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

In Situ Investigation of Si-TPA-MFI Crystallization Using (Ultra-) Small- and Wide-Angle X-ray Scattering

et al. 1997

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“…This is probably due to the high alkalinity of the synthesis medium in which a considerable part of the silica would remain in the solution phase rather than crystallizing as silicalite-1. Schoeman et al [21] noted that at high alkalinities the rate of crystal dissolution relative to the growth rate is expected to be larger than at a lower alkalinity. As a result of this fact the lower silica conversion can be expected at high alkalinity in consequence of high TPAOH concentration in the synthesis medium.…”

Section: Resultsmentioning

confidence: 98%

“…TPAOH. In the synthesis studies from a clear solution [7,21] it was observed that crystals grow from subcolloidal particles of size around 5 nm. Since centrifugation conditions used in our study is not sufficient to recover such small particles the percent conversion were obtained as zero at the beginning of the synthesis.…”

Section: Resultsmentioning

confidence: 99%

Crystallization of silicalite‐1 from clear synthesis solutions: Effect of template concentration on crystallization rate and crystal size

Soydaş

Culfaz

Kalıpçılar

et al. 2009

Cryst. Res. Technol.

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Synthesis of silicalite-1 powders and membranes from initially clear solutions with different tetrapropylammonium hydroxide or bromide concentrations was studied. While tetrapropylammonium bromide acts only as template, tetrapropylammonium hydroxide provides both the template and hydroxyl ions to the synthesis medium. The effects of template and hydroxyl ion concentration on the product yield, crystallization rate and crystal size were investigated. Pure and highly crystalline silicalite-1 was obtained with all compositions. The nucleation time decreases from 100 h to 20 h and the crystal size decreases from 3.5 µm to 0.35 µm as the template amount x is increased from 5 to 30 moles at a batch composition of 80SiO 2 .xTPAOH.1500H 2 O at 95 °C. Yield of silicalite-1 passes through a maximum at intermediate TPA concentration.

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“…The crystallization of zeolite nanocrystals is normally performed at the lowest possible temperature with a relatively long synthesis period [3], e.g., silicalite nanocrystals with a size of ca. 90 and 30 nm were produced hydrothermally from a clear solution at 80-115°C for several days [4][5][6][7] or by aging the clear solution at room temperature for 30 days and subsequently heating it to 90°C for a few hours [8]. A two-stage, variable-temperature synthesis procedure was developed to produce silicalite nanocrystals with a size of ca.…”

Section: Introductionmentioning

confidence: 99%

Rapid Crystallization of Silicalite Nanocrystals in a Capillary Microreactor

et al. 2009

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Silicalite nanocrystals were synthesized in a pressurized capillary microreactor at 150°C within 11 min with synthesis solutions aged at 80 or 100°C for 1-6 h. The effects of aging of the synthesis solution and the reaction pressure were examined. The resulting products were characterized by XRD, DLS, TEM, FT-IR and TG-DSC. Aging of the synthesis solution played an important role in shortening the crystallization time of the silicalites. The synthesis pressure should be higher than the saturation vapor pressure of water at 150°C (∼0.5 MPa) and silicalite nanocrystals with crystallinities of 70 % and 100 % could be produced from the synthesis solution aged at 100°C for 2 h with residence times of 11 min at 0.7 MPa and 1 MPa, respectively. The mean particle sizes of these two samples were 102.2 nm and 166.4 nm, respectively. Thus, the crystallization time of the silicalite nanocrystals is shown to be significantly reduced in the capillary microreactor compared to a traditional batch system.

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Analysis of the crystal growth mechanism of TPA-silicalite-1

Cited by 120 publications

References 14 publications

In Situ Investigation of Si-TPA-MFI Crystallization Using (Ultra-) Small- and Wide-Angle X-ray Scattering

In Situ Investigation of Si-TPA-MFI Crystallization Using (Ultra-) Small- and Wide-Angle X-ray Scattering

Crystallization of silicalite‐1 from clear synthesis solutions: Effect of template concentration on crystallization rate and crystal size

Rapid Crystallization of Silicalite Nanocrystals in a Capillary Microreactor

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