Ultraviolet—Visible Spectroscopy

Weckhuysen, Bert M.

doi:10.1002/chin.200521298

Cited by 7 publications

(8 citation statements)

References 30 publications

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“…Structural and chemical characterization (coordination, oxidation state, and dispersion) of solid catalysts is now possible via numerous spectroscopic techniques, such as XANES (X-ray absorption near-edge spectroscopy), EXAFS (extended X-ray absorption fine structure), solid-state NMR (nuclear magnetic resonance), ESR (electron spin resonance), UV–vis (ultraviolet–visible), FTIR (Fourier transform infrared), Raman, and XPS (X-ray photoelectron spectroscopy), along with chemisorption and TPR (temperature-programmed reduction) , methods. Among these, UV–vis spectroscopy − and TPR techniques − are particularly attractive for structural characterization of catalysts since they require relatively inexpensive equipment that are easy to use and readily available in most catalysis research laboratories.…”

Section: Introductionmentioning

confidence: 99%

“…Even in cases where these limitations are overcome, quantification is still a challenge because reference compounds and molar absorption coefficients of most supported species are not readily available. Nevertheless, UV–vis spectroscopy, when cleverly used, can provide a wealth of catalyst structural information (e.g., metal coordination, oxidation state, and dispersion), − which would otherwise be only available with less ubiquitous techniques, such as solid-state NMR, XPS, XANES, and EXAFS. TPR characterization of catalysts, when carried out properly (i.e., in the absence of transport limitations and with appropriately selected experimental conditions for optimum reduction profiles), − can also provide useful information about the presence of bulk and surface phases, degree of reduction, metal–support interactions, alloy formation, metal content, valence of metallic species, and, in some cases, mechanism, kinetics, and activation energy of reduction. − In the absence of complementary spectroscopic techniques, interpretations of TPR profiles for structural information (e.g., coordination, oxidation state, and dispersion) can be difficult.…”

Section: Introductionmentioning

confidence: 99%

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Ultraviolet–Visible Spectroscopy and Temperature-Programmed Techniques as Tools for Structural Characterization of Cu in CuMgAlO_xMixed Metal Oxides

2012

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Ultraviolet–visible (UV–vis) spectroscopy was used in combination with temperature-programmed reduction (TPR) methods to provide information about the Cu structure in CuMgAlO x mixed oxides. UV–vis spectra revealed the presence of highly dispersed, isolated and oligomeric, CuO species in a distorted octahedral environment. From these spectra, optical absorption edge energies were determined and correlated with the number of nearest CuO neighbors (a measure of CuO domain size) and Cu content in the mixed oxides. Increasing the Cu content from 4 to 21 at. % increased the number of nearest CuO neighbors in oligomeric CuO from about 2 to 4 and produced materials that were more easily reducible, as inferred from TPR of untreated and N2O-passivated CuMgAlO x . A further increase in Cu content to 38 at. % increased the number of nearest CuO neighbors to 4.5 but resulted in a decrease of reducibility because of the evolution of an amorphous CuO phase in the bulk of the mixed oxides. This work represents the first demonstration of combining UV–vis spectroscopy with TPR of untreated and N2O-passivated CuMgAlO x as a relatively simple and inexpensive methodology for in-depth structural characterization of Cu in mixed metal oxides from which the composition, domain size, and relative fraction of total (surface + bulk) and surface oligomeric CuO species can be determined. A methodology that allows assessment of the extent of CuO bulk enrichment in CuMgAlO x materials is also presented.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ultraviolet–Visible Spectroscopy and Temperature-Programmed Techniques as Tools for Structural Characterization of Cu in CuMgAlO_xMixed Metal Oxides

2012

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“…In situ UV-vis spectroscopy has proved to be useful for the study of PO synthesis at reaction conditions, 10,12,13,37 and recent reviews provide useful descriptions of the technique. 49,50 In this work, in situ transient UV-vis data are used to identify the formation of Ti-hydroperoxide species and to verify its characteristic behavior as a reaction intermediate. In situ XAFS spectroscopy is another powerful technique that can be used to obtain atom-specific structural and electronic information from solid inorganic catalysts under operating conditions.…”

Section: Introductionmentioning

confidence: 99%

Transient Technique for Identification of True Reaction Intermediates: Hydroperoxide Species in Propylene Epoxidation on Gold/Titanosilicate Catalysts by X-ray Absorption Fine Structure Spectroscopy

et al. 2008

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In situ ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy was used in combination with in situ Ti K-edge X-ray absorption near-edge structure (XANES) to study the formation of Ti-hydroperoxo species during the gas-phase epoxidation of propylene with H 2 and O 2 at reaction conditions over a Au-Ba/Ti-SiO 2 (Ti-TUD) catalyst. The in situ UV-vis measurements showed growth of a signal due to Ti-hydroperoxo species when the catalyst was put in contact with H 2 /O 2 /Ar (1/1/8) and C 3 H 6 /H 2 /O 2 /Ar (1/1/1/7) gas mixtures at 423 K and 0.1 MPa. Changes in the area of the pre-edge peak centered at 4968.9 eV present in the Ti K-edge XANES spectra of the catalyst were used to estimate the Ti-hydroperoxo species coverages (θ) under operating conditions. Transient Ti K-edge XANES experiments with H 2 /O 2 /Ar (1/1/8) and C 3 H 6 /H 2 /O 2 /Ar (1/1/1/7) gas mixtures allowed the estimation of the net epoxidation rate by a novel method involving the determination of dθ/dt. It is shown that the Ti-hydroperoxo species are true intermediates because their initial rate of reaction measured from the in situ transient XANES data (3.4 × 10 -4 s -1 ) has the same order of magnitude as the steady-state turnover frequency for propylene epoxidation based on the total Ti (2.5 × 10 -4 s -1 ) measured in a catalytic flow reactor. This is the first use of XANES to measure the turnover rate of a catalyzed reaction.

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“…Spectroscopy in the electromagnetic spectrum regions of ultraviolet (UV), visible (Vis) and near infrared (NIR) is often called electronic spectroscopy due to transfer of electrons from low-energy to high-energy orbitals when the light is irradiated to material [138]. In these methods, the intensity of light that passes through the sample is measured.…”

Section: Uv-vis Spectroscopymentioning

confidence: 99%

Instrumental approach toward understanding nano-pollutants

Naghdi

Metahni

Ouarda

et al. 2017

Nanotechnol. Environ. Eng.

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Nano-pollutants (NPLTs) have recently raised global concerns due to their possible harmful impact on environment and human health. However, until date, information on the occurrence, fate and toxicity of NPLTs in environment is scant. The knowledge gap can be attributed to the lack of advanced and sophisticated methodologies for the precise detection and characterization of NPLTs at lower concentration in complex matrices, such as surface water, wastewater, soil and food. This review briefly discusses the performance of classical methods for characterization and study of the properties of NPLTs. The important properties include shape, size, aggregation state, chemical composition and structure. Chromatographic, microscopic and spectroscopic techniques have been developed for detection and quantitative estimation of fabricated or naturally existed NPLTs in different matrices. Often, combination of these techniques is required for the separation, purification and accurate estimation. For better detection and understanding of the initial steps of interaction with the environmental matrices, pollution sources, such as wastewater and industrial discharges, must be selected as sampling points. Understanding the dynamics of agglomeration, and decantation will allow to estimate the plume of transport to delimit the potential effects.

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Ultraviolet—Visible Spectroscopy

Abstract: For Abstract see ChemInform Abstract in Full Text.

Cited by 7 publications

References 30 publications

Ultraviolet–Visible Spectroscopy and Temperature-Programmed Techniques as Tools for Structural Characterization of Cu in CuMgAlO_xMixed Metal Oxides

Ultraviolet–Visible Spectroscopy and Temperature-Programmed Techniques as Tools for Structural Characterization of Cu in CuMgAlO_xMixed Metal Oxides

Transient Technique for Identification of True Reaction Intermediates: Hydroperoxide Species in Propylene Epoxidation on Gold/Titanosilicate Catalysts by X-ray Absorption Fine Structure Spectroscopy

Instrumental approach toward understanding nano-pollutants

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Ultraviolet—Visible Spectroscopy

Abstract: For Abstract see ChemInform Abstract in Full Text.

Cited by 7 publications

References 30 publications

Ultraviolet–Visible Spectroscopy and Temperature-Programmed Techniques as Tools for Structural Characterization of Cu in CuMgAlOxMixed Metal Oxides

Ultraviolet–Visible Spectroscopy and Temperature-Programmed Techniques as Tools for Structural Characterization of Cu in CuMgAlOxMixed Metal Oxides

Transient Technique for Identification of True Reaction Intermediates: Hydroperoxide Species in Propylene Epoxidation on Gold/Titanosilicate Catalysts by X-ray Absorption Fine Structure Spectroscopy

Instrumental approach toward understanding nano-pollutants

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Product

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Ultraviolet–Visible Spectroscopy and Temperature-Programmed Techniques as Tools for Structural Characterization of Cu in CuMgAlO_xMixed Metal Oxides

Ultraviolet–Visible Spectroscopy and Temperature-Programmed Techniques as Tools for Structural Characterization of Cu in CuMgAlO_xMixed Metal Oxides