TEM Observation of Aggregation Steps in Room-Temperature Silicalite-1 Zeolite Formation

Liang, Duoduo; Follens, Lana; Aerts, Alexander; Martens, Johan A.; Tendeloo, Gustaaf Van; Kirschhock, Christine

doi:10.1021/jp074960k

Cited by 42 publications

(49 citation statements)

References 19 publications

(33 reference statements)

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“…Typical molar composition space for silicalite-1 in the system SiO2-TPAOH-H2O occurring either in concentrated media (yellow area) as investigated by Corkery, van Santen, and Cundy et al [12,13,24,59], or dilute systems (blue area) as studied by Davis, Tsapatsis, and Shantz et al [3,22,27,28,41,42,50,51,60,61]. Both domains have also been extensively explored by Nikolakis, Lobo, and Martens et al [1,2,4,10,14,17,20,25,26,62].…”

Section: Introductionmentioning

confidence: 98%

“…However, the very early stages of zeolite formation lies in the pre-heating stage, at precursor formation. Since their discovery in the mid 1990s many controversial studies have attempted to derive the exact status of the very early nanoparticles of small size in the range a few nanometers [2,3,[12][13][14][15][16][17][18][19][20][21]. The question of whether these nanoparticles contain occluded organic templates or are simply organic-free silica entities has been disputed [9] and a core-shell structure with a negatively charged surface silica core surrounded by a shell of organocations, might seem to be the most accepted description [1,2,10,15,[22][23][24][25][26][27][28][29][30].…”

Section: Introductionmentioning

confidence: 99%

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Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

et al. 2016

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Abstract:The dynamic behavior of tetrapropylammonium (TPA) cations in the clear precursor sols for silicalite synthesis has been investigated by 1 H diffusion ordered spectroscopy (DOSY), T 1 , T 2 , and T 1ρ 1 H relaxation, as well as 1 HÑ 13 C cross polarization (CP) nuclear magnetic resonance. The DOSY NMR experiments showed the presence of strong solute-solvent interactions in concentrated sols, which are decreasing upon dilution. Similarities in dependence of diffusion coefficients with fractional power of the viscosity constant observed for nanoparticles, TPA cations and water led to the conclusion that they aggregate as anisotropic silicate-TPA particles. Relaxation studies as well as 1 HÑ 13 C CP experiments provide information on dynamic properties of ethanol, water and TPA cations, which are function of silicate aggregates. The general tendency showed that the presence of silicate as oligomers and particles decreases the relaxation times, in particular T 2 and T 1ρH , as a consequence of involvement of these latter in ion-pairing interactions with water-solvated TPA molecules slowing down their mobility. Furthermore, from the 1 HÑ 13 C CP dynamics curve profiles a change in the CP transfer regime was observed from fast (T CH << T 1ρH ) for solutions without silicates to moderate (T CH~T1ρH ) when silicates are interacting with the TPA cations that may reflect the occlusion of TPA into flexible silicate hydrate aggregates.

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

et al. 2016

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“…The formation of silicalite-1 is extremely slow at ambient temperature and takes months to years. [2][3][4] By heating a clear sol, for example, at 90 8C, the crystallization time of colloidal silicalite-1 is shortened to about one day.…”

Section: Introductionmentioning

confidence: 99%

“…[3,[10][11][12] Nanoslab-shaped nanoparticles have been observed after spreading the clear sol on a TEM grid. [4] Based on the variety of experimental approaches and investigations of clear sols, several models for the crystallization of silicalite-1 have been proposed. The rival models differ in the nature of the silicate species responsible for crystal growth, the extent of zeolitic order within the nanoparticles, and the involvement of aggregation steps.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the Mechanism of Colloidal Silicalite‐1 Crystallization by Using DLS, SAXS, and ²⁹Si NMR Spectroscopy

Aerts

Haouas

Caremans

et al. 2010

Chemistry A European J

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127

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Colloidal silicalite-1 zeolite was crystallized from a concentrated clear sol prepared from tetraethylorthosilicate (TEOS) and aqueous tetrapropylammonium hydroxide (TPAOH) solution at 95 degrees C. The silicate speciation was monitored by using dynamic light scattering (DLS), synchrotron small-angle X-ray scattering (SAXS), and quantitative liquid-state (29)Si NMR spectroscopy. The silicon atoms were present in dissolved oligomers, two discrete nanoparticle populations approximately 2 and 6 nm in size, and crystals. On the basis of new insight into the evolution of the different nanoparticle populations and of the silicate connectivity in the nanoparticles, a refined crystallization mechanism was derived. Upon combining the reagents, different types of nanoparticles (ca. 2 nm) are formed. A fraction of these nanoparticles with the least condensed silicate structure does not participate in the crystallization process. After completion of the crystallization, they represent the residual silicon atoms. Nanoparticles with a more condensed silicate network grow until approximately 6 nm and evolve into building blocks for nucleation and growth of the silicalite-1 crystals. The silicate network connectivity of nanoparticles suitable for nucleation and growth increasingly resembles that of the final zeolite. This new insight into the two classes of nanoparticles will be useful to tune the syntheses of silicalite-1 for maximum yield.

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“…[45][46][47][48] Three representative samples were selected for HRTEM study: the precursor, the sample which has obvious frequency lag, and the sample which has nearly equal Raman frequencies ( Figure 6, samples a-c, respectively). The HRTEM images of sample a show that mixing of the initial reactants resulted in an open network of large, nonuniform gel particles, which www.chemeurj.org is composed of globules with a diameter ranging between 15 and 20 nm (Figure 8 a).…”

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confidence: 99%

From Molecular Fragments to Crystals: A UV Raman Spectroscopic Study on the Mechanism of Fe‐ZSM‐5 Synthesis

Fan

Sun

Feng

et al. 2009

Chemistry A European J

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The nucleation process of iron-exchanged zeolite Fe-ZSM-5, from the assembly of distorted tetrahedrally coordinated iron species and silicate rings in the precursor to the final Fe-ZSM-5 crystals, as well as variations in the coordination environment of iron, were studied by UV resonance Raman spectroscopy and complementary techniques.The entire sequence of crystallization events of Fe-ZSM-5 was monitored by UV Raman spectroscopy in combination with HRTEM, UV/Vis spectroscopy, X-ray diffraction patterns, and periodic DFT calculations. Fe-ZSM-5 was synthesized by an organic-free method to avoid signal interference from the organic template in Raman spectra. Framework iron atoms with resonance Raman bands at 516, 1115, and 1165 cm(-1), and a Raman band at 1016 cm(-1) are detected for Fe-ZSM-5. In the early stage of Fe-ZSM-5 synthesis, the precursor contains iron atoms in distorted tetrahedral coordination and five- and six-membered silicate rings. Nucleation by aggregation of the precursor species was monitored by UV Raman spectroscopy based on the resonance Raman effect, and confirmed by periodic DFT calculations. Evolution of iron species on the surface and in the bulk phase was monitored by UV Raman spectroscopy with excitation at 244 and 325 nm, as well as HRTEM. Nucleation takes place first in the core of the amorphous particles, and crystalline nuclei with Fe-ZSM-5 structure are formed in the core by consuming the amorphous shell. Finally the amorphous particles are completely transformed into Fe-ZSM-5 crystals.

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TEM Observation of Aggregation Steps in Room-Temperature Silicalite-1 Zeolite Formation

Cited by 42 publications

References 19 publications

Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

Investigation of the Mechanism of Colloidal Silicalite‐1 Crystallization by Using DLS, SAXS, and ²⁹Si NMR Spectroscopy

From Molecular Fragments to Crystals: A UV Raman Spectroscopic Study on the Mechanism of Fe‐ZSM‐5 Synthesis

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TEM Observation of Aggregation Steps in Room-Temperature Silicalite-1 Zeolite Formation

Cited by 42 publications

References 19 publications

Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

Investigation of the Mechanism of Colloidal Silicalite‐1 Crystallization by Using DLS, SAXS, and 29Si NMR Spectroscopy

From Molecular Fragments to Crystals: A UV Raman Spectroscopic Study on the Mechanism of Fe‐ZSM‐5 Synthesis

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Investigation of the Mechanism of Colloidal Silicalite‐1 Crystallization by Using DLS, SAXS, and ²⁹Si NMR Spectroscopy