Homogeneous Catalytic Processes Monitored by Combined in Situ ATR-IR, UV–Vis, and Raman Spectroscopy
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The benefit of coupling in situ spectroscopic methods (attentuated total reflectance-infrared spectroscopy (ATR-IR), Raman, and UV–vis) for the real-time monitoring of homogeneously catalyzed reactions is exemplarily demonstrated on selected examples of use. In this context, the different mode of catalyst action in reduction reactions of imides and amides with phenylsilanes will be discussed. In the iron-catalyzed decomposition of formic acid, different intermediate iron complexes were identified and the inhibiting effect of chloride onto active iron complex formation could be elucidated. Furthermore, it could be shown that in a Lewis acid catalyzed cyclocondensation reaction, the reactant activation proceeds differently with AlCl3 and TiCl4. For the described in situ spectroscopic studies, a versatile setup was used which allows the simultaneous registration of ATR-IR, UV–vis, and Raman spectra in small volumes of solution at different reaction-determined conditions using fiber-optic probes for the each spectroscopy.Keywords:
Attenuated total reflection
Water-in-oil (w/o) emulsions are of great interest in many areas including food technology and the oil and gas industry. However, the molecular mechanisms that lead to a stable emulsion are yet to be fully understood. In this article, the potential of attenuated total reflection (ATR) infrared (IR) spectroscopy for studying the influence of an emulsifier on the molecular water structure in a thin layer at the w/o interface is demonstrated. For this purpose, IR spectra from a bilberry extract w/o emulsion are analyzed. The thickness of the probed water layer is estimated to be below 0.5 μm, which is well below the droplet diameter. The IR spectra recorded in aqueous solution and the w/o emulsion reveal a strengthening of the intramolecular covalent O-H bonds in the presence of the emulsifier, which in turn indicates a change in the hydrogen bond network in terms of weakening the intermolecular interactions in the water layer at the interface.
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Infrared spectroscopy is widely used to analyse the surface of solid materials central to modern chemical processes. For liquid phase experiments, the attenuated total reflection mode (ATR-IR) requires the use of waveguides that can limit a broader applicability of the technique for catalysis studies. Here, we demonstrate that high quality spectra of the solid-liquid interface can be collected in diffuse reflectance mode (DRIFTS) thus opening future applications of infrared spectroscopy.
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Abstract Stationary and modulated IR-ATR spectra of Schiff's base nematic liquid crystals are reported. The mean order parameter of both, the aromatic core and the hydrocarbon chains is determined by analysis of the infrared dichroism of characteristic absorption bands. Hydrocarbon chain ordering was found to be considerably lower than predicted by Marčelja's statistical theory.
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Infrared spectral analysis is a commonly used means to research the characteristics of mineral material. Attenuated total internal reflectance infrared spectroscopy (ATR -FTIR) is widely used dues to its advantages such as rapidness, non-destructiveness and micro region detection. This paper focuses on different areas of amber, copal resin, coated amber to further study its ATR-FTIR through the BRUKER LUMOS independent type infrared microscope. The result shows: the two infrared absorption spectrum which are 1 643 cm-1 due to stretching vibration of ν(CC) and 889 cm-1 due to deformation vibration of δ(arene C—H)are present in the amber originated in Dominica and Russia; the infrared absorption spectrum band lies at 1 300～925 cm-1 due to stretching vibration of ν(C—O) has a certain instruction significance for the origin of amber; the three absorption spectrum of 3 080 cm-1 which is due to dis-symmetry stretching vibration of νas(CH2), 1 643 and 887 cm-1 can be used as characteristic of copal resin and have identification significance; coated amber displays amber and artificial resin mixing infrared spectrum, which besides the characteristic infrared spectrum of amber, 760 and 702 cm-1 infrared spectrum are caused by out-plane bending vibration of γ(arene C—H) of resin. ATR-FTIR has important significance in the identification of cause, origin and enhancement varieties of amber.
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In this article, the historical development of spectroscopy is examined and the spectroscopy devices used today are described. Then, we focus on infrared (IR) spectroscopy, which cannot give valuable signal in aqueous solution. Attenuated total reflection (ATR)-IR technique solves the problem. In addition, we specifically mention newly developed disposable ATR-IR crystals and micromachined silicon (Si) ATR-IR. Disposable crystal systems and microfluidics systems can be integrated with existing miniature ATR analyzers. If the integration is successful, the technique might be used in biomedical measuring instruments, reactions' analyses, and ultra-high-pressure analyses.
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Attenuated total reflection (ATR) spectroscopy has been shown to eliminate many of the difficulties encountered in the past with the sample presentation for infrared analysis. Yarn orientation behavior at different draw ratios was studied by analysis of polarized infrared spectra. The data demonstrate that the α conformation increases with drawing for nylon 6,6 fibers. The chain conformation and crystallite orientation which occur during drawing of nylon 6,6 fibers are also demonstrated. The structural changes observed by the present technique seem to agree well with x-ray diffraction data.
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The initial oligomerization of bis(hydroxyethyl terephthalate), BHET, was monitored in situ at 220, 250, and 270 °C by attenuated total reflection (ATR)/infrared (IR) and near-infrared (NIR) transmission spectroscopy. The obtained sets of IR and NIR spectra, which include information about the progress of the reaction, were analyzed by means of generalized two-dimensional (2D) correlation spectroscopy. Both 2D IR and 2D NIR correlation spectra clearly identified bands at 1030, 880, and 861 cm-1 (IR region) and 5830 cm-1 (NIR region) arising from ethylene glycol (EG), which is expelled out of the system during the reaction. The synchronous hetero 2D NIR−IR correlation spectrum showed positive cross-peaks between the IR peaks at 1030, 880, and 861 cm-1 and the NIR band at 5830 cm-1 while no cross-peak appeared in the corresponding asynchronous spectrum, confirming that all these peaks arise from the same origin (EG). To carry out the 2D hetero correlation analysis, the experiment was modified so that both ATR/IR and NIR probes could be employed simultanously. The 2D NIR correlation analysis also suggested that a band at 5260 cm-1 is ascribed to water. It was found that NIR spectroscopy may be very useful to in situ monitor the amount of water in the reaction system.
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The attenuated total refraction infrared spectroscopy(ATR-FTIR)is an important experimental method,it greatly expands the application fields of infrared spectroscopy.Several kinds of polymer materials were analysed by ATR-FTIR.The infrared spectrum characteristic peaks can effecticely determine the type of polymer.Infrared spectroscopy can also be applied in the composition determination of the copolymer or blend.
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