Raman Scattering Theory and Elements of Raman Instrumentation

Colomban, Philippe; Gouadec, Gwénaël

doi:10.1002/9780470475997.ch2

Cited by 3 publications

(3 citation statements)

References 29 publications

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“…53−56 The position of ν(M-(η 2 -O 2 )) shifts to lower wavenumbers from Ti-BEA 53 to Nb-BEA, Mo-BEA, and W-BEA 54 due to greater charge transfer from the group 6 metal center to the peroxide moiety. 57 In addition to features that appear only after contact with H 2 O 2 , spectra for Mo-and W-BEA possess a distinct feature near 970 cm −1 (Figure 2), which is attributed to ν(MO) 58,59 and is absent from spectra of Ti-BEA and Nb-BEA. Mo-BEA and W-BEA also show Raman features reminiscent of oligomeric metal oxides complexes including bridging M−O−M bonds at 700 cm −159 and 805 cm −1 for WO 3 and 880 cm −1 for MoO 3 .…”

Section: Methodssupporting

confidence: 87%

“…The Raman spectra of H 2 O 2 -activated Ti-, Nb-, Mo-, and W-BEA contain features between 550 and 620 cm –1 that correspond to the symmetric and asymmetric stretching modes of metal-peroxo (M-(η 2 -O 2 )) intermediates. − The position of ν(M-(η 2 -O 2 )) shifts to lower wavenumbers from Ti-BEA to Nb-BEA, Mo-BEA, and W-BEA due to greater charge transfer from the group 6 metal center to the peroxide moiety . In addition to features that appear only after contact with H 2 O 2 , spectra for Mo- and W-BEA possess a distinct feature near 970 cm –1 (Figure ), which is attributed to ν(MO) , and is absent from spectra of Ti-BEA and Nb-BEA.…”

Section: Resultsmentioning

confidence: 99%

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Alkene Epoxidations with H₂O₂ over Groups 4–6 Metal-Substituted BEA Zeolites: Reactive Intermediates, Reaction Pathways, and Linear Free-Energy Relationships

et al. 2020

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Rates and selectivities for alkene epoxidations depend sensitively on the identity of the active metal center for both heterogeneous and homogeneous catalysts. While group 6 metals (Mo, W) have greater electronegativities and the corresponding molecular complexes have greater rates for epoxidations than group 4 or 5 metals and molecular complexes, these relationships are not established for zeolite catalysts. Here, we combine complementary experimental methods to determine the effects of metal identity on the catalytic epoxidation of 1hexene with H 2 O 2 for active sites within the BEA framework. Postsynthetic methods were used to incorporate groups 4−6 transition-metal atoms (Ti, Nb, Mo, W) into the framework of zeolite BEA. In situ Raman and UV−vis spectroscopies show that H 2 O 2 activates to form peroxides (M-(η 2 -O 2 )) and hydroperoxides (M-OOH) on all M-BEA but also metal oxos (MO) on W-and Mo-BEAs, the latter of which leaches rapidly. Changes in turnover rates for epoxidation as functions of reactant concentrations and the conformation of cis-stilbene epoxidation products indicate that epoxide products form by kinetically relevant O-atom transfer from M-OOH or M-(η 2 -O 2 ) intermediates to the CC bond and show two distinct kinetic regimes where H 2 O 2 -derived intermediates or adsorbed epoxide molecules prevail on active sites. Ti-BEA catalyzes epoxidations with turnover rates 60 and 250 times greater than Nb-BEA and W-BEA, which reflect apparent activation enthalpies (ΔH ‡ ) for both epoxidation and H 2 O 2 decomposition that are lower for Ti-BEA than for Nb-and W-BEAs. Values of ΔH ‡ for epoxidation differ much more between metals than barriers for H 2 O 2 decomposition and give rise to large differences in 1hexene epoxidation selectivities that range from 93% on Ti-BEA to 20% on W-BEA. Values of ΔH ‡ for both pathways scale linearly with measured enthalpies for adsorption of 1,2-epoxyhexane from the solvent to active sites measured by isothermal titration calorimetry. These correlations confirm that linear free-energy relationships hold for these systems, despite differences in the coordination of active metal atoms to the BEA framework, the identity and number of pendant oxygen species, and the complicating presence of solvent molecules.

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Section: Methodssupporting

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Alkene Epoxidations with H₂O₂ over Groups 4–6 Metal-Substituted BEA Zeolites: Reactive Intermediates, Reaction Pathways, and Linear Free-Energy Relationships

et al. 2020

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“…The first one was characteristic of the chemical bond at the origin of the signal, the second parameter was related to the concentration of vibrating bonds, and the last one was correlated to the disorder of the material and, especially in case of polymer, it allowed differentiating crystalline and amorphous phases. [58] In what follows we will particularly focus on two signals, the band at 1,000 cm −1 , which was common to monomer and polymer and the band at 1,631 cm −1 , which was specific to monomer (Figure 1b). We will establish quantitative relations between the characteristics of these bands and monomer conversion during emulsion polymerization.…”

Section: Resultsmentioning

confidence: 99%

In situ conversion monitoring of styrene emulsion polymerization by deconvolution of a single reference band near 1,000 cm⁻¹

Dropsit

Hoppe

Chapron

et al. 2019

J Raman Spectroscopy

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Styrene emulsion polymerization was performed in batch reactor using Raman spectroscopy for in situ monitoring of styrene conversion. The variation of the band of trigonal aromatic ring breathing at 1,000 cm−1 was analyzed in detail as a function of monomer conversion (wavenumber, integrated intensity, and half‐width at half‐maximum). The observed variation was described both qualitatively and quantitatively by a model assuming that the overall signal resulted from the addition of two close and distinct Gaussian signals, one originating from the monomer and the other one from the polymer repeat units. A reliable estimation of monomer conversion was obtained using the relative contributions of both components. The results were comparable to those obtained using the ratio of integrated intensities of the band at 1,000 cm−1 (overlapping signals of monomer and polymer) and the band at 1,631 cm−1 (signal specific to monomer). It was shown experimentally that information about monomer conversion could be obtained by applying linear model mixture to a single band of Raman spectrum, which provided an alternative method to the use of a ratio of integrated intensities.

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Analytical performance of Raman spectroscopy in assaying biochemical components in human serum

et al. 2021

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Raman Scattering Theory and Elements of Raman Instrumentation

Cited by 3 publications

References 29 publications

Alkene Epoxidations with H₂O₂ over Groups 4–6 Metal-Substituted BEA Zeolites: Reactive Intermediates, Reaction Pathways, and Linear Free-Energy Relationships

Alkene Epoxidations with H₂O₂ over Groups 4–6 Metal-Substituted BEA Zeolites: Reactive Intermediates, Reaction Pathways, and Linear Free-Energy Relationships

In situ conversion monitoring of styrene emulsion polymerization by deconvolution of a single reference band near 1,000 cm⁻¹

Analytical performance of Raman spectroscopy in assaying biochemical components in human serum

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Raman Scattering Theory and Elements of Raman Instrumentation

Cited by 3 publications

References 29 publications

Alkene Epoxidations with H2O2 over Groups 4–6 Metal-Substituted BEA Zeolites: Reactive Intermediates, Reaction Pathways, and Linear Free-Energy Relationships

Alkene Epoxidations with H2O2 over Groups 4–6 Metal-Substituted BEA Zeolites: Reactive Intermediates, Reaction Pathways, and Linear Free-Energy Relationships

In situ conversion monitoring of styrene emulsion polymerization by deconvolution of a single reference band near 1,000 cm−1

Analytical performance of Raman spectroscopy in assaying biochemical components in human serum

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Product

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Alkene Epoxidations with H₂O₂ over Groups 4–6 Metal-Substituted BEA Zeolites: Reactive Intermediates, Reaction Pathways, and Linear Free-Energy Relationships

Alkene Epoxidations with H₂O₂ over Groups 4–6 Metal-Substituted BEA Zeolites: Reactive Intermediates, Reaction Pathways, and Linear Free-Energy Relationships

In situ conversion monitoring of styrene emulsion polymerization by deconvolution of a single reference band near 1,000 cm⁻¹