Initial Steps of the Sol−Gel Process: Modeling Silicate Condensation in Basic Medium

Henschel, H.; Schneider, Andreas; Prosenc, Marc H.

doi:10.1021/cm100401f

Cited by 36 publications

(58 citation statements)

References 49 publications

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“…10 −5 mbar inside the hexapole collision cell. Consequently, the exchange of the bridging oxygen atom is most likely only feasible when oxygen atom scrambling occurs through a strained, four‐membered cyclic disiloxane intermediate (Scheme ) . The surprising finding that this exchange is observed in the gas phase, but not in solution, may be rationalized by several marked differences in the environments: the species investigated in the gas phase is not the neutral siloxanediol, but the corresponding anion.…”

Section: Resultsmentioning

confidence: 99%

Reactivity of the Sterically Demanding Siloxanediol Mes₂Si(OH)(μ‐O)Si(OH)Mes₂ Towards Water and Ether Molecules

Roesch

Warzok

Enke

et al. 2017

Chemistry A European J

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A series of isotopologues of the siloxanediol Mes Si(OH)(μ-O)Si(OH)Mes (3 a) (Mes=2,4,6-trimethylphenyl) were synthesized by reactions of the corresponding disiloxane precursors Mes Si(μ-O) SiMes (2 a), Mes Si(μ- O) SiMes (2 b) or Mes Si(μ- O) SiMes (2 c) with an excess of H O, H O or H O. NMR and IR signal assignments for the siloxanediols in benzene are supported by quantum-chemical calculations, which indicate small energy differences between trans and cis conformers, the latter of which exhibits an intramolecular hydrogen bond. H NMR as well as IR data suggest the presence of a mixture of both conformers in C D . Hydrogen-bonded adducts of Mes Si(OH)(μ-O)Si(OH)Mes with ethers such as diethylether, dimethoxyethane or dioxane were observed in the solid state, where they form polymeric chain-like structures. The latter appear to be stable only in the crystal. O{ H} NMR and IR data in THF solution suggest an interaction of 3 a with at least one THF molecule, whereas diethylether appears not to interact. Water adducts form neither in solution nor in the solid state as indicated by NMR and ATR IR data. O{ H} NMR and ESI-MS experiments illustrate the remarkably high stability of the siloxanediols towards water and show no evidence for intra- or intermolecular oxygen-exchange reactions. In marked contrast, a stepwise exchange of all three oxygen atoms-including the one in the Si-O-Si bridge-occurred in the gas phase, when [Mes Si( OH)(μ- O)Si( O)Mes ] was treated with H O in the hexapole of an ESI FT-ICR mass spectrometer. The scrambling between the bridging and the other oxygen atoms likely proceeds through cyclic Si O intermediates.

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Section: Resultsmentioning

confidence: 99%

Reactivity of the Sterically Demanding Siloxanediol Mes₂Si(OH)(μ‐O)Si(OH)Mes₂ Towards Water and Ether Molecules

Roesch

Warzok

Enke

et al. 2017

Chemistry A European J

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“…[30]. This mechanism was also supported by the work of Henschel et al and Hu et al [31,32]. Thomson et al investigated the mechanism for condensation of silicic acid to form linear dimer and trimer, cyclic trimer and tetramer, prismatic hexamer and cubic octamer [33].…”

Section: Introductionmentioning

confidence: 83%

“…It is generally believed that oligomerization of silicic acid during the hydrothermal process is crucial for nucleation and growth of the zeolite framework [45]. Due to the complexity of the structures of potential oligomers of silicic acid, only small oligomers containing less than six Si atoms has been investigated, and the results are still hard to render the zeolite formation and growth mechanism [25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45]. The oligomerization of poly-silicic acids was considered selective and the formation of some poly-silicic acids as precursors for zeolite framework would be either kinetics- or thermodynamics-driven [18,19,20].…”

Section: Introductionmentioning

confidence: 99%

Oligomerization of Silicic Acids in Neutral Aqueous Solution: A First-Principles Investigation

Liu

Meng

2019

IJMS

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Crystallite aluminosilicates are inorganic microporous materials with well-defined pore-size and pore-structures, and have important industrial applications, including gas adsorption and separation, catalysis, etc. Crystallite aluminosilicates are commonly synthesized via hydrothermal processes, where the oligomerization of silicic acids is crucial. The mechanisms for the oligomerization of poly-silicic acids in neutral aqueous solution were systematically investigated by extensive first-principles-based calculations. We showed that oligomerization of poly-silicic acid molecules proceeds through the lateral attacking and simultaneously proton transfer from the approaching molecule for the formation of a 5-coordinated Si species as the transition state, resulting in the ejection of a water molecule from the formed poly-silicic acid. The barriers for this mechanism are in general more plausible than the conventional direct attacking of poly-silicic acid with reaction barriers in the range of 150–160 kJ/mol. The formation of linear or branched poly-silicic acids by intermolecular oligomerization is only slightly more plausible than the formation of cyclic poly-silicic acids via intramolecular oligomerization according to the reaction barriers (124.2–133.0 vs. 130.6–144.9 kJ/mol). The potential contributions of oligomer structures, such as the length of the linear oligomers, ring distortions and neighboring linear branches, etc., to the oligomerization were also investigated but found negligible. According to the small differences among the reaction barriers, we proposed that kinetic selectivity of the poly-silicic acids condensation would be weak in neutral aqueous solution and the formation of zeolite-like structures would be thermodynamics driven.

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“…The implicit solvation models have been successfully applied in relevant systems such as aluminosilicate clusters [26][27][28][29] and sol-gel process of silicate. 24 Catlow and his colleages [26][27][28][29] have shown the reliability of another similar implicit solvation approachthe conductor-like screening model (COSMO) approach Table 1. Changes of Gibbs free energies (∆G) and enthalpies (∆H) [kJ mol -1 ] at 338.15 K for successive deprotonation reactions of neutral complexes Si(OH) 4 and NaAl(OH) 4 with OH -or NaOH calculated at M06-2X/6-311++G** level.…”

Section: Methodsmentioning

confidence: 99%

Dissolution and Absorption: A Molecular Mechanism of Mesopore Formation in Alkaline Treatment of Zeolite

et al. 2014

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Aiming to optimize alkaline treatment of zeolites to obtain hierarchical zeolites, dissolution and absorption mechanisms relevant to mesopore formation were investigated at an atomistic scale by density functional calculations. In the dissolution processes, dealumination is energetically more favourable than desilication though both processes can occur. The dissolved Al species prefer to be absorbed back onto zeolite surfaces whereas the dissolved Si species tend to aggregate in solution. The dissolution process promotes but the absorption process hampers the mesopore formation, laying foundation for understanding the mesoporosity influenced by the variations of zeolite framework and solution.

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Initial Steps of the Sol−Gel Process: Modeling Silicate Condensation in Basic Medium

Cited by 36 publications

References 49 publications

Reactivity of the Sterically Demanding Siloxanediol Mes₂Si(OH)(μ‐O)Si(OH)Mes₂ Towards Water and Ether Molecules

Reactivity of the Sterically Demanding Siloxanediol Mes₂Si(OH)(μ‐O)Si(OH)Mes₂ Towards Water and Ether Molecules

Oligomerization of Silicic Acids in Neutral Aqueous Solution: A First-Principles Investigation

Dissolution and Absorption: A Molecular Mechanism of Mesopore Formation in Alkaline Treatment of Zeolite

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Initial Steps of the Sol−Gel Process: Modeling Silicate Condensation in Basic Medium

Cited by 36 publications

References 49 publications

Reactivity of the Sterically Demanding Siloxanediol Mes2Si(OH)(μ‐O)Si(OH)Mes2 Towards Water and Ether Molecules

Reactivity of the Sterically Demanding Siloxanediol Mes2Si(OH)(μ‐O)Si(OH)Mes2 Towards Water and Ether Molecules

Oligomerization of Silicic Acids in Neutral Aqueous Solution: A First-Principles Investigation

Dissolution and Absorption: A Molecular Mechanism of Mesopore Formation in Alkaline Treatment of Zeolite

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Reactivity of the Sterically Demanding Siloxanediol Mes₂Si(OH)(μ‐O)Si(OH)Mes₂ Towards Water and Ether Molecules

Reactivity of the Sterically Demanding Siloxanediol Mes₂Si(OH)(μ‐O)Si(OH)Mes₂ Towards Water and Ether Molecules