Mechanisms of methanol adsorption on silicalite and silica: IR spectra and ab-initio calculations

Pelmenschikov, A. G.; Morosi, Gabriele; Gamba, Aldo; Zecchina, A.; Bordiga, Silvia; Паукштис, E. A.

doi:10.1021/j100148a023

Cited by 81 publications

(95 citation statements)

References 10 publications

(14 reference statements)

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“…The exchange of some atop Si-H groups with atop Si-OCH 3 groups is demonstrated by the appearance of a CH 3 symmetric (∼2840 cm -1 ) and two CH 3 asymmetric (∼2940 and ∼2980 cm -1 ) stretching modes, a decrease in the intensity of, and a red-shift in, the Si-H stretching mode (∼2080 cm -1 ), the appearance of the CH 3 umbrella distortion (1190 cm -1 ), and the appearance of a complex mode involving an O-C stretching motion coupled with a C-H bending motion (∼1090 cm -1 ). 47,49,50,59,66 The broadening (the full width at half-max increases up to 20 cm -1 ) and red-shifting (by about 6 cm -1 ) of the remaining Si-H stretching modes indicates that dipole-dipole coupling between neighboring Si-H species is being disrupted. [67][68][69][70] This observation is consistent with random exchange of Si-H sites to Si-OCH 3 sites over the entire surface rather than the formation of separated domains of isolated Si-H and Si-OCH 3 groups.…”

Section: Resultsmentioning

confidence: 99%

Investigation of the Chemical Purity of Silicon Surfaces Reacted with Liquid Methanol

et al. 2008

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The reaction of hydrogen-terminated Si(111) and oxide-terminated silicon surfaces with neat anhydrous liquid methanol (CH 3 OH) has been studied with Fourier transform infrared spectroscopy (FTIR) as a function of solution temperature and immersion time. At 65°C, reaction of atomically smooth H-Si(111) surfaces with CH 3 OH (l) results in partially methoxylated silicon surfaces that are free of any detectable subsurface oxidation (Si-O-Si bonds); this is in contrast to observable oxidation found after similar reactions on H-Si(100) surfaces. At long reaction times (t > 3 h), the Si(111) surface saturates with Si-OCH 3 sites at a coverage of approximately 30% of a monolayer, with the residual ∼70% comprised of unreacted Si-H sites. The lack of any detectable silicon oxide makes it possible to conclude the following: (i) Reaction mechanisms involving insertion of oxygen atoms from the CH 3 OH molecule into the subsurface Si-Si back bonds cannot be dominant for (111)-oriented silicon under these conditions. (ii) The vibrational modes of the oxide-free surface are very sharp and can be clearly distinguished from blue-shifted modes observed for methoxyl groups chemisorbed on oxidized surfaces. For surfaces that display subsurface oxidation, no evidence for oxygen atoms directly below atop Si-H sites has been observed. Instead, FTIR analysis demonstrates that subsurface oxidation selectively exists underneath atop Si-OCH 3 sites. Finally, H-terminated oxide surfaces, prepared by reacting trichlorosilanes on OH-terminated SiO 2 surfaces, react with methanol to form a methoxy-terminated oxide surface.

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Section: Resultsmentioning

confidence: 99%

Investigation of the Chemical Purity of Silicon Surfaces Reacted with Liquid Methanol

et al. 2008

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“…4). Table 4 shows that the frequencies calculated using the HF/6-31G** method are in best agreement with experiment, but one should rather consider the frequency shifts between free and adsorbed methanol [39] (Table 5).…”

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confidence: 79%

Theoretical investigation of the adsorption of methanol on the (110) surface of γ -alumina

Vito

Gilardoni

Kiwi‐Minsker

et al. 1999

Journal of Molecular Structure: THEOCHEM

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The adsorption of methanol on the (110) surface of g -alumina was investigated using both ab initio and density functional theory quantum chemical methods. A [Al 3 O 9 H 10 ] ϩ cluster model comprising one tetrahedral and two octahedral aluminum cations were used to describe the surface and the mechanism of adsorption of methanol. This has allowed us to rationalize the stable structures of adsorbate and the mode of bonding. The IR frequency shifts between the gas phase and the adsorbed species were also calculated and they exhibit good agreement with experiment. ᭧

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“…22,23 Numerous experimental and theoretical studies have investigated both these solid/alcohol and solid/alcohol vapor interfaces. [23][24][25][26] More recently, VSFS and other 2 nd order nonlinear optical methods have been employed to study molecular-level interactions at buried silica/liquid alcohol interfaces. 20,[27][28][29][30][31][32] Using this surface specific technique, vibrational modes of species in asymmetric environments have been observed and used to discern the structure and organization of interfacial molecules.…”

Section: Introductionmentioning

confidence: 99%

Unusual Structure and Dynamics at Silica/Methanol and Silica/Ethanol Interfaces—A Molecular Dynamics and Nonlinear Optical Study

et al. 2015

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Vibrational sum frequency (VSF) spectroscopy and molecular dynamics simulations are used to investigate ethanol-silica and methanol-silica interfaces. We describe the subtle differences in molecular organization that result in different VSF spectra obtained at the alcohol-silica liquidsolid interfaces. Alcohol molecules hydrogen bonded to the silica surface induce orientational opposition in an adjacent low-population region, which implies VSF signal reduction. This low population region is essentially of zero density in the ethanol system, suggesting less signal cancellation. Simulated silica defect sites increase the population of this region in both systems.Interestingly, the induced orientation in this region influences subsequent molecular orientation only in the ethanol-silica system, preserving the interfacial anisotropy. These effects suggest a stronger VSF response from the ethanol-silica system versus the methanol-silica system, where more methanol molecules reside in the low-population region and this region does not induce order in subsequent solvent layers.

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Mechanisms of methanol adsorption on silicalite and silica: IR spectra and ab-initio calculations

Cited by 81 publications

References 10 publications

Investigation of the Chemical Purity of Silicon Surfaces Reacted with Liquid Methanol

Investigation of the Chemical Purity of Silicon Surfaces Reacted with Liquid Methanol

Theoretical investigation of the adsorption of methanol on the (110) surface of γ -alumina

Unusual Structure and Dynamics at Silica/Methanol and Silica/Ethanol Interfaces—A Molecular Dynamics and Nonlinear Optical Study

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