Influence of Aging and Dilution on the Crystallization of Silicalite-1

Moor, de Pea; Beelen, Tpm Theo; Santen, van Ra Rutger

doi:10.1107/s002188989700174x

Cited by 12 publications

(14 citation statements)

References 13 publications

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“…Although there is significant scattering in this value in literature, all values are well above the activation energy of 12-17 kJ/ mol which is to be expected for a diffusion-controlled growth mechanism. 17 In a previous study, 18 we found the conversion of SiO 2 to MFI to be independent of the concentration of the synthesis mixture, which also means that the crystal growth is not diffusion controlled. This is in accord with the abundant presence of the primary units and with a growth mechanism where the integration of the primary units at the crystal surface is the rate-limiting step.…”

Section: Discussionmentioning

confidence: 85%

In situ Observation of Nucleation and Crystal Growth in Zeolite Synthesis. A Small-Angle X-ray Scattering Investigation on Si-TPA-MFI

1999

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The formation and consumption of nanometer scale precursor particles during the hydrothermal synthesis of Si-TPA-MFI from a clear solution has been studied in situ using a combination of X-ray scattering techniques and with electron microscpy. The combination of wide-, small-, and ultra-small-angle X-ray scattering allowed us to obtain information on a continuous range of length scales spanning over four orders of magnitude (0.17−6000 nm), covering all particle populations present during the complete course of the crystallization process. The use of high-brilliance synchrotron radiation allows us to perform time-resolved experiments. Two types of precursor particles were observed: 2.8 nm sized primary units and aggregates (≈10 nm). Variation of the alkalinity of the synthesis mixture revealed a strong correlation between the concentration of the aggregates and the rate of the crystal nucleation. The presence of the 2.8 nm sized primary units appears to be independent on the alkalinity. The addition of seed crystals to a synthesis mixture that does not show spontaneous nucleation (no aggregates observed) resulted in normal crystal growth. The size distribution of the growing crystals could be followed in situ by fitting calculated scattering patterns to experimental curves and showed good agreement with electron microscopy results. The apparent activation energy for crystal growth is determined to be 83 kJ/mol by following in situ the crystal growth process at various reaction temperatures. These data show that the formation of aggregates of primary units is an essential step in the nucleation process and suggest that the crystal growth step is the reaction-controlled inclusion of the 2.8 nm sized primary units at the crystal surface.

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Section: Discussionmentioning

confidence: 85%

In situ Observation of Nucleation and Crystal Growth in Zeolite Synthesis. A Small-Angle X-ray Scattering Investigation on Si-TPA-MFI

1999

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“…TPA. The crystallization of Si-MFI from clear water synthesis mixtures with TPA as a structure-directing agent, studied with small-angle X-ray scattering techniques has been reported extensively by us in previous publications. ,,− The most relevant results for comparison with the current study are published in ref .…”

Section: Resultsmentioning

confidence: 95%

Si-MFI Crystallization Using a “Dimer” and “Trimer” of TPA Studied with Small-Angle X-ray Scattering

Moor¹,

Beelen²,

Santen³

et al. 2000

J. Phys. Chem. B

146

130

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The formation and consumption of precursors and the crystallization of Si-MFI using bis(tripropylammonium) hexamethylene dihydroxide (“dimer” of tetrapropylammonium cation, TPA) and bis(tripropylammonium-N-N‘-hexamethylene)-N‘ ‘,N‘ ‘-dipropylammonium trihydroxide (“trimer” of TPA) as structure-directing agents have been investigated in situ using simultaneous, time-resolved, SAXS and WAXS and using USAXS. The formation of 2.8-nm-sized primary units is observed upon dissolution of the silica source, which is in agreement with results from earlier studies on systems with the TPA cation as a structure-directing agent. Aggregation of these nanometer-scale primary units to 10−15-nm-sized particles is found to be an essential step in nucleation of the zeolite. Crystal growth occurs via the addition of the primary units to the growing crystal. Although the size of the primary units for MFI is independent of the structure-directing agent used, the organic species does have a pronounced influence on the crystal growth step and, therefore, on the crystal growth rate, size, and morphology. The results presented here confirm a common mechanism proposed for organic-mediated crystallization of high-silica zeolites.

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“…The heating stage was mounted in an Anton Paar HR-PHK sample chamber, and the whole system was purged with helium (>99.99%) several times and then operated under vacuum (0.1 mbar). The scattered intensity of the particles was calculated on the basis of using water (room temperature and 368 K individually) as the reference material for the background subtraction in data analysis. , For obtaining the transmission coefficient of the sample, a piece of glassy carbon was inserted into the beam path as a second specimen after each measurement and was taken every three measurements. The transmission coefficients were almost identical during the process of the hydrothermal reaction.…”

Section: Methodsmentioning

confidence: 99%

“…Zeolites are widely used in adsorption, ion-exchange processes, and heterogeneous catalysis. − It is this (and potentially other applications) that spurs the intense research effort into understanding their nucleation and growth. Silicalite-1, the all-silica form of ZSM-5, is one of the most widely studied zeolite systems. − The nucleation and growth of silicalite-1, particularly from “clear solution” synthesis mixtures containing only tetrapropylammonium hydroxide TPAOH, tetraethyl orthosilicate (TEOS), and water, have been investigated using a battery of methods including nuclear magnetic resonance spectroscopy (NMR), − dynamic light scattering (DLS), − ,,− and small-angle X-ray/neutron scattering (SAXS/SANS). − ,,,− Silicalite-1 nucle...…”

Section: Introductionmentioning

confidence: 99%

“…The nucleation and growth of silicalite-1, particularly from "clear solution" synthesis mixtures containing only tetrapropylammonium hydroxide TPAOH, tetraethyl orthosilicate (TEOS), and water, have been investigated using a battery of methods including nuclear magnetic resonance spectroscopy (NMR), [9][10][11] dynamic light scattering (DLS), [23][24][25]27,[31][32][33][34][35][36] and small-angle X-ray/neutron scattering (SAXS/SANS). [12][13][14][15][16][17][18]37,38,[42][43][44][45] Silicalite-1 nucleation and crystallization kinetics are highly dependent on temperature, 37,46 organocation identity, 18,47,48 silica source and content, 24,26,49 alkalinity of the solution, 14 and the presence of alkali cations. 50 Furthermore, the organocation's properties also influence zeolite formation, for example, the hydrophobicity, 51,52 the ability to form van der Waals contact with silicate species, 9,11 and the geometry of the organocation.…”

Section: Introductionmentioning

confidence: 99%

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Silicalite-1 Growth from Clear Solution: Effect of Alcohol Identity and Content on Growth Kinetics

Cheng

Shantz

2005

J. Phys. Chem. B

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In situ small-angle X-ray scattering (SAXS) is used to investigate the influence of alcohol identity and content on silicalite-1 growth from clear solutions at 368 K. Several tetraalkyl orthosilicates (Si(OR)4, R = Me, Pr, and Bu) are used to synthesize silicalite-1 from clear solution mixtures comparable to those previously investigated (i.e. 1:0.36:20 TEOS:TPAOH:H2O (TEOS = tetraethyl orthosilicate; TPAOH = tetrapropylammonium hydroxide), 368 K). All TPAOH-organosiloxane mixtures studied form silica nanoparticles after aging at room temperature for 24 h. Full-profile fitting analysis of the SAXS data indicates the particles are ellipsoidal and is inconsistent with the presence of "nanoslabs" or "nanoblocks". Synthesis using TEOS as the silica source have an induction period of approximately 7.5 h and a growth rate of 1.90 +/- 0.10 nm/h at 368 K. Changing the silica source to tetramethyl orthosilicate (TMOS) does not change the induction period; however the particle growth rate is decreased to 1.65 +/- 0.09 nm/h at 368 K. Variable-temperature SAXS measurements for syntheses with TEOS and TMOS show the activation energy for silicalite-1 growth is 60.0 +/- 2.9 and 73.9 +/- 2.8 kJ/mol, respectively, indicating the alcohol identity does influence the growth rate. By mixing tetrapropyl orthosilicate (TPOS) with TEOS (1.6:1.0 molar ratio) as the silica source, the precursor solution shows a shorter induction period (6.0 h) and a faster particle growth rate (2.16 +/- 0.06 nm/h). The alcohol identity effect is more pronounced when other organocations (e.g. alkyltripropylammonium cations) are used to make silicalite-1 at 368 K. Removing ethanol from the precursor solution decreases the induction period to approximately 4.5 h and increases the particle growth rate to 2.99 +/- 0.13 nm/h. Mixtures with 2 equiv of ethanol have an induction period and particle growth rate of 6.0 h and 2.04 +/- 0.03 nm/h, respectively. The results demonstrate the alcohol identity and content influence silicalite-1 growth kinetics. One possible explanation is varying the alcohol identity and content changes the strength of the hydrophobic hydration of the structure-directing agent and the water-alcohol interaction, resulting in less efficient interchange between clathrated water molecules and solvated silicate species.

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Influence of Aging and Dilution on the Crystallization of Silicalite-1

Cited by 12 publications

References 13 publications

In situ Observation of Nucleation and Crystal Growth in Zeolite Synthesis. A Small-Angle X-ray Scattering Investigation on Si-TPA-MFI

In situ Observation of Nucleation and Crystal Growth in Zeolite Synthesis. A Small-Angle X-ray Scattering Investigation on Si-TPA-MFI

Si-MFI Crystallization Using a “Dimer” and “Trimer” of TPA Studied with Small-Angle X-ray Scattering

Silicalite-1 Growth from Clear Solution: Effect of Alcohol Identity and Content on Growth Kinetics

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