Infrared reflection

IRRAS Infrared reflection- Grazing-incidence polarized Enhanced sensitivity... 

Vibrational Spectroscopy. Infrared absorption spectra may be obtained using convention IR or FTIR instrumentation the catalyst may be present as a compressed disk, allowing transmission spectroscopy. If the surface area is high, there can be enough chemisorbed species for their spectra to be recorded. This approach is widely used to follow actual catalyzed reactions see, for example. Refs. 26 (metal oxide catalysts) and 27 (zeolitic catalysts). Diffuse reflectance infrared reflection spectroscopy (DRIFT S) may be used on films [e.g.. Ref. 28—Si02 films on Mo(llO)]. Laser Raman spectroscopy (e.g.. Refs. 29, 30) and infrared emission spectroscopy may give greater detail [31]. 

Szanyi J, Kuhn W K and Goodman D W 1994 CO oxidation on palladium 2. A combined kinetic-infrared reflection absorption spectroscopic study of Pd(IOO) J. Phys. Chem. 98 2978... 

A number of new technology promotion options are being explored in the lighting area. Work is undeiway on market transformation programs based on bulk procurement for improved efficacy incandescent light bulbs and for compact fluorescent lamps and fixtures. For incandescent lamps, adaptations of the infrared reflective lamp coating that is already in use on reflector bulbs are encouraged by the EPAct requirement. 

Dale, J.M., Klatt, L.N., "Principal Component Analysis of diffuse Near-Infrared Reflectance Data From Paper Currency", / /)/. Spec. 1989 (43) 1399-1405. 

Mark, H., "Normalized distances for Qualitative Near-Infrared Reflectance Analysis", Anal. Chem. 1986 (58) 379-384. 

In situ Fourier transform infrared and in situ infrared reflection spectroscopies have been used to study the electrical double layer structure and adsorption of various species at low-index single-crystal faces of Au, Pt, and other electrodes.206"210 It has been shown that if the ions in the solution have vibrational bands, it is possible to relate their excess density to the experimentally observed surface. 

KJ. Uram, L. Ng, and J.R.Yates Jr., Electrostatic effects between adsorbed species-The K-CO interaction on Ni(lll) as studied by infrared reflection - absorption spectroscopy, Surf. Sci. 177, 253-277 (1986). 

Coatings for photothermal solar converters with high infrared reflectance, which use Reaction (3) and a 1000°C anneal,... 

Lucovsky G, White RM, Benda JA, ReveUi JE (1973) Infrared-reflectance spectra of layered Group-IV and Group-VI transition-metal dichalcogenides. Phys Rev B 7 3859-3870 Cordes H, Schmid-Fetzer R (1994) Phase equilibria in the U-Te system. J AUoy Compd 216 197-206... 

Tkachuk, R. et ah. Determination of chlorophyll in ground rapeseed using a modified near infrared reflectance spectrophotometer, J. Am. Oil Chm. Soc., 65, 381, 1988. 

Recent work in our laboratory has shown that Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) can be used routinely to measure vibrational spectra of a monolayer on a low area metal surface. To achieve sensitivity and resolution, a pseudo-double beam, polarization modulation technique was integrated into the FT-IR experiment. We have shown applicability of FT-IRRAS to spectral measurements of surface adsorbates in the presence of a surrounding infrared absorbing gas or liquid as well as measurements in the UHV. We now show progress toward situ measurement of thermal and hydration induced conformational changes of adsorbate structure. The design of the cell and some preliminary measurements will be discussed. 

Reaction products can also be identified by in situ infrared reflectance spectroscopy (Fourier transform infrared reflectance spectroscopy, FTIRS) used as single potential alteration infrared reflectance spectroscopy (SPAIRS). This method is suitable not only for obtaining information on adsorbed products (see below), but also for observing infrared (IR) absorption bands due to the products immediately after their formation in the vicinity of the electrode surface. It is thus easy to follow the production of CO2 versus the oxidation potential and to compare the behavior of different electrocatalysts. 

It is only since 1980 that in situ spectroscopic techniques have been developed to obtain identification of the adsorbed intermediates and hence of reliable reaction mechanisms. These new infrared spectroscopic in situ techniques, such as electrochemically modulated infrared reflectance spectroscopy (EMIRS), which uses a dispersive spectrometer, Fourier transform infrared reflectance spectroscopy, or a subtractively normalized interfacial Fourier transform infrared reflectance spectroscopy (SNIFTIRS), have provided definitive proof for the presence of strongly adsorbed species (mainly adsorbed carbon monoxide) acting as catalytic poisons. " " Even though this chapter is not devoted to the description of in situ infrared techniques, it is useful to briefly note the advantages and limitations of such spectroscopic methods. 

The different species formed by steps (18) to (20) or (18 ) to (20 ) have been detected by in situ infrared reflectance spectroscopy, and such dissociative steps are now widely accepted even if the exact nature of the species formed during (20) or (20 ) is still a subject of discussion. Several groups proposed the species (COH)3js as the main, strongly adsorbed species on the platinum surface, even though no absorption infrared band can be definitely attributed to (COH),, . However, the formyl-like species ( CHO), , . has been formally identified, since it gives an IR absorption band ataroimd 1690cm . ... 

The different kinds of adsorbed CO were observed by in situ infrared reflectance spectroscopy. The results showed that using bulk Pt-Ru alloys, the adsorbed CO species formed by dissociation of methanol, or from dissolved CO on the surface of the electrode, are different on R and on Ru. The adsorption of CO occurs on pure Pt and Ru and on alloys of different compositions, but a shift detected in the wave number of the... 

These conclusions from the infrared reflectance spectra recorded with Pt and Pt-Ru bulk alloys were confirmed in electrocatalysis studies on small bimetallic particles dispersed on high surface area carbon powders.Concerning the structure of bimetallic Pt-Ru particles, in situ Extended X-Ray Absorption Fine Structure (EXAFS>XANES experiments showed that the particle is a true alloy. For practical application, it is very important to determine the optimum composition of the R-Ru alloys. Even if there are still some discrepancies, several recent studies have concluded that an optimum composition about 15 to 20 at.% in ruthenium gives the best results for the oxidation of methanol. This composition is different from that for the oxidation of dissolved CO (about 50 at.% Ru), confirming a different spatial distribution of the adsorbed species. 

Westermark, G. and Persson, 1. (1998) Chemisorption of tertiary phosphines on coinage and platinum group metal powders. An infrared reflectance absorption spectroscopic, enhanced Raman spectroscopic and surface coverage study. Colloids and Surfaces A -Physicochemical and Engineering Aspects, 144, 149-166. 

EMIRS electrochemically modulated infrared reflectance spectroscopy... 

In the early work of Bewick and Robinson (1975), a simple monochromator system was used. This is called a dispersive spectrometer. In the experiment the electrode potential was modulated between two potentials, one where the adsorbed species was present and the other where it was absent. Because of the thin electrolyte layer, the modulation frequency is limited to a few hertz. This technique is referred to as electrochemically modulated infrared reflectance spectroscopy (EMIRS). The main problem with this technique is that data acquisition time is long. So it is possible for changes to occur on the electrode surface. 

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