Structure and properties of disiloxane: An ab initio and post‐Hartree–Fock study

Derzi, Afaf R. Al; Gregušová, Adriana; Runge, Keith; Bartlett, Rodney J.

doi:10.1002/qua.21720

Cited by 14 publications

(40 citation statements)

References 37 publications

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“…The geometries were optimized using the second-order Møller-Plesset (MP2) perturbation theory with 6-311G++ (2d,2p) basis set. A disiloxane molecule has been generally applied for theoretical investigations of crystalline and amorphous silicates (e.g., Xiao and Lasaga, 1994;Al Derzi et al, 2008;Morrow et al, 2009;Noritake and Kawamura, 2015). In the study, therefore, the disiloxane molecule was assumed as the simplest interior structural unit of SiO 2 .…”

Section: Experimental Methodsmentioning

confidence: 99%

Carbon substitution for oxygen in α–cristobalite

Mitani

Kyono

2017

Journal of Mineralogical and Petrological Sciences

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We investigated the carbon solubility into silica under high temperature condition. Mixtures of amorphous silica and graphite powder sealed in silica glass tubes were heated at 1300°C. The a lattice parameter and unit cell volume of α-cristobalite obtained are slightly increased compared with that heated without graphite. The c lattice parameter, on the other hand, almost unchanged. There is no clear dependency of the lattice parameter variations on carbon content mixed as the starting material. After re-heating the samples under atmospheric oxygen, the a lattice parameter and unit cell volume were reduced from the previous values. These changes indicate the possibility that carbon certainly incorporated into the α-cristobalite was oxidized with the atmospheric oxygen. The ab-initio calculation of disiloxane molecule showed that with carbon substitution for the bridging oxygen the Si-C bond distance increases whereas the Si-C-Si bond angle decreases compared with the Si-O bond distance and Si-O-Si bond angle. Consequently, the distance between Si atoms increases with the carbon substitution for the bridging oxygen. Since the expansion of Si-Si distance contributes twice as much to the a and b-axes than the c-axis in the unit cell of α-cristobalite, the ab-initio simulation result supports the observation that a lattice parameter increases with the carbon substitution relative to the c lattice parameter. The study strongly suggests that under reduced and high temperature conditions carbon is substituted not for silicon but for oxygen in α-cristobalite structure.

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Section: Experimental Methodsmentioning

confidence: 99%

Carbon substitution for oxygen in α–cristobalite

Mitani

Kyono

2017

Journal of Mineralogical and Petrological Sciences

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“…28,30,32,33 The reasons are most probably the size of the structure (288 independent atoms if P 1 symmetry is considered, as in a single Ti substitution per unit cell) and the flexibility of the MFI framework intrinsically connected to the wide range of bond angles and energies which Si-O-Si angle can span. [36][37][38][39] The former drawback has been progressively overcome, following the evolution of both computational resources and codes. Instead, the latter remains an intrinsic problem of the MFI topology, which must be necessarily addressed.…”

Section: Indroductionmentioning

confidence: 99%

“…As reported in several benchmark studies involving simple models of the Si-O-Si moiety, its correct description in terms of both geometrical and energetic features requires to adopt post Hartree-Fock methods together with large basis sets. [36][37][38][39] DFT is in general giving a poorer geometrical description, whereas it gives reasonable energetic values. 38 Furthermore, it is worth to mention that Silicalite-1 is often a defective material, i.e.…”

Section: Geometrical Featuresmentioning

confidence: 99%

Computational Assessment of Relative Sites Stabilities and Site-Specific Adsorptive Properties of Titanium Silicalite-1

et al. 2018

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Titanium Silicalite-1 (TS-1), because of its crystalline structure and its well-defined Ti sites, represents the prototype of a single site catalyst. According to this fundamental aspect and to the relevant role of TS-1 as selective catalyst in important industrial partial oxidation reactions, TS-1 has been widely characterized through both experimental and computational techniques. Still, several fundamental aspects of its structural and catalytic properties have to be addressed. Among these, an intriguing topic is the Ti location in the various sites of the MFI framework. The independent sites are generally considered to be 12, following the Pnma space group of TS-1 at high Ti loading. However, when Ti loading is lower than 2 atoms per unit cell, diffraction showed as the system must be described by the P2 1 /n space group, thereby allowing 24 independent sites. With respect to previous studies, this work aims to exploit this datum to give a more accurate description of the TS-1 system at low Ti loadings, adopting a state of the art methodology (all electron periodic B3LYP-D2 calculations). The relative stabilities of the 24 Ti sites have been evaluated, showing a good agreement with previous studies. The simulation of adsorption energies for ammonia (present as reactants in some of the most important industrial reactions catalyzed by TS-1) over the most stable sites have been computed as well, in order to validate the obtained models. Additionally to binding energies, adsorption enthalpies and Gibbs free energies have been obtained through an approximate reduced Hessian scheme. The improved local description of the Ti sites (in combination with the adducts stabilities given by the energetic data) allowed the deep understanding of subtle effects, such as the number of molecular ligands each Ti atom can actually host upon adsorption. These results, showing only few sites can efficiently host two ligands in the neighborhoods of STP conditions, allowed for the first time the heterogeneity in the experimental outcomes reported over the last two decades to be rationalized.

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“…A disiloxane molecule (Si 2 O 7 H 6 , dimer structure) has been extensively applied in theoretical investigations of crystalline and amorphous silicates (e.g., Xiao and Lasaga, 1994;Al Derzi et al, 2008;Morrow et al, 2009;Noritake and Kawamura, 2015;Mitani and Kyono, 2017). We assumed the disiloxane molecule to be the simplest interior structural unit of the amorphous silica in this study.…”

Section: First-principles Calculationsmentioning

confidence: 99%

Pressure–induced crystallization of biogenic hydrous amorphous silica

Kyono

Yokooji

Chiba

et al. 2017

Journal of Mineralogical and Petrological Sciences

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Samples of the diatom Nitzschia cf. frustulum, collected from Lake Yogo, Siga Prefecture, Japan, were cultured in the laboratory. Organic components of the diatom cell were removed by washing with acetone and sodium hypochlorite. The remaining frustules were studied by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared (FTIR) spectroscopy, and synchrotron X-ray diffraction. The results showed that the spindle-shaped diatom frustule was composed of hydrous amorphous silica. Pressure-induced phase transformation of the diatom frustule was investigated by in situ Raman spectroscopic analysis. With exposure to 0.3 GPa at 100°C, the Raman band corresponding to quartz occurred at ν = 465 cm −1 . In addition, a characteristic Raman band for moganite was observed at 501 cm −1 . From the integral ratio of Raman bands, the moganite content in the probed area was estimated to be approximately 50 wt%. With increased pressure and temperature, the initial morphology of diatom frustules was totally changed to a characteristic spherical particle with a diameter of about 2 µm. Increasing pressure to 5.7 GPa at 100°C resulted in the appearance of a Raman band assignable to coesite at 538 cm −1 . That is, with compression and heating, hydrous amorphous silica can be readily crystallized into quartz, moganite, and coesite. First-principles calculations revealed that a disiloxane molecule with a trans configuration is twisted 60°with a close approach of a water molecule, which leads to a trans to cis configuration change. It is therefore reasonable to assume that during crystallization of hydrous amorphous silica, an Si-O-Si bridging unit with the cis configuration would survive as a structural defect, and could subsequently crystallize into moganite by maintaining that geometry. This hypothesis is adaptable to the phase transformation from hydrous amorphous silica to coesite as well, because coesite has four-membered rings and is easily formed from hydrous amorphous silica under high pressure and temperature conditions.

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Structure and properties of disiloxane: An ab initio and post‐Hartree–Fock study

Cited by 14 publications

References 37 publications

Carbon substitution for oxygen in α–cristobalite

Carbon substitution for oxygen in α–cristobalite

Computational Assessment of Relative Sites Stabilities and Site-Specific Adsorptive Properties of Titanium Silicalite-1

Pressure–induced crystallization of biogenic hydrous amorphous silica

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