Diffuse reflectance IR spectroscopy

The possibility of using surface modification of cheap metals to make them effective electrode materials has been mentioned (Section 57.3.2.3(1)). A further example employs cyanoferrates and cyanoruthenates as the redox centres.76 Complexes such as [M(CN)5L]" (M = Fe, Ru L = CN, H20, NO, L-histidine) may be immobilized on a partially corroded nickel surface. The surfaces have good stability and diffuse reflectance IR spectroscopy shows the presence of bridging cyano groups, implying the presence of a binuclear (Ni, M) species in the surface. A general equation for the redox reaction is ... 

Kustov, L. M., Borovkov, V. Y. and Kazanskii, V. B. Study of ethylene oligomerization on Brpnsted and Lewis acidic sites of zeolites using diffuse reflectance IR spectroscopy. Stud. Surf. Sci. Catal., 1984, 18, 241-247. 

Diffuse reflectance IR spectroscopy has become an attractive alternative to mulls with the introduction of DRIFT cell by Griffiths,29 later modified by Yang.30 Since materials are dispersed in a nonabsorbing medium and not subjected to thermal or mechanical energy during sample preparation, DRIFT spectroscopy is especially suitable for the qualitative/quantitative analysis for polymorphs, which are prone to solid-state transformations. The Kubelka-Munk (K-M) equation,31 which is analogous to Beer s law for transmission measurements, is used to quantitatively describe diffusely-reflected radiation ... 

Diffuse reflection IR spectroscopy was used for determination of grafted amount of polymer. It was evaluated using calibration curves plotted from the absorbency spectra of the samples, made from a mixture of the polymer and particles (50 mg). The characteristic band at 1493 cm-1 was chosen for this estimation. 

Methyl chloride is an important industrial product, having a global annual capacity of ca. 900 000 tons. Its primary use is for the manufacture of more highly chlorinated materials such as dichloromethane and chloroform and for the production of silicone fluids and elastomers. It is usually manufactured by the reaction of methanol with hydrogen chloride with a suitable acid catalyst, such as alumina. To develop a site-specific reaction mechanism and a kinetics model for the overall process, one first needs to identify all the reagents present at the catalyst surface and the nature of their interactions with the surface. The first step in the reaction is dissociative adsorption of methanol to give adsorbed methoxy species. Diffuse reflectance IR spectroscopy (29d) showed the expected methoxy C-H stretch and deformations, but an additional feature, with some substructure, at 2600 cm was... 

Fig. 431 Calibration curve for the presence of cefepime dihydrochloride dihydrate in cefepime dihydrochloride monohydrate as determined by diffuse reflectance IR spectroscopy. (From Bugay 1999, with permission.)...

For ferromagnetic cobalt particles in zeolite X, spin-echo ferromagnetic resonance has been used to obtain unique structural information (S6). In addition, study of the catalytic signature of metal/zeolite catalysts has been used by the groups of Jacobs (87), Lunsford (88), and Sachtler (47,73,89). Brpnsted acid protons are identified by their O—H vibration (90,91) in FTIR or indirectly, by using guest molecules such as pyridine or trimethylphosphine (92,93). An ingenious method to characterize acid sites in zeolites was introduced by Kazansky et al., who showed by diffuse reflection IR spectroscopy that physisorbed H2 clearly discerns different types of acid sites (94). Also, the weak adsorption of CO on Brpnsted and Lewis acid sites has been used for their identification by FTIR (95). The characterization of the acid sites was achieved also by proton NMR (96). 

Lewis basic sites in alkaline forms of zeolites are studied by diffuse-reflectance IR spectroscopy using adsorbed molecular probes, such as fluoroform, chloroform, acetylene, and its derivatives RC=CH. Chloroform and compounds containing C-H fragments near the triple bond are shown to be the most sensitive and efficient molecular probes. 

Diffuse reflectance IR spectroscopy has been used, in conjunction with XRPD analysis, to determine the levels of ranitidine Form-II in samples of... 

Studies of Molecular Sieve Catalysis by Diffuse Reflectance IR Spectroscopy... 

Surface moisture is a problem of concern in ceramic powders, and IR has been used to characterize the surface groups of -OH and -H [58,63,64]. IR was also applied to characterize chemically bound hydrogen in chemical vapor-deposited silicon nitride at various ammonia-silane ratios [65]. Surface silicon dioxide on SiC powders was determined by photoacoustic IR and diffuse reflectance IR spectroscopy [66,67]. IR spectroscopy was also used to study the surface oxidation of SiC and SisN4 [68,69]. 

Diffuse reflectance IR spectroscopy (DRIFT) was, furthermore, successfully employed in studying molecular sieves of the new generation [957] such as aluminophosphates (AlPOs) and silicoaluminophosphates (SAPOs). Thus, Zscherpel et al. and Loeffler et al. [563,564] studied by DRIFT the range of fundamental OH stretching, OH deformation and framework vibrations of AIPO4-18 (upon decomposition of the template, tetraethylanunonium hydroxide), the fundamental and combination vibrations of hydroxy groups of SAPO-5 and SAPO-17 as well as the framework region of SAPO-34. In the latter case a comparison was made with the transmission spectrum. 

In diffuse reflectance IR spectroscopy (DRIFT) light impinges on a solid powdered sample and is scattered in all directions. This light is collected and redirected to a detector. The powder must be very fine and is mixed with or dispersed in a suitable matrix, such as KCl or KBr with a particle size of less than 10 pm. It is not suitable for large powders or lumps. By using special sample preparation techniques, e.g., by placing the KBr powder over the sample, monolayers of adsorbed silanes have been studied [55], or water adsorbed on polymer surfaces has been detected [56]. 

Ivanov, A.V., Kustov, L.M. (1998). Investigation of the State of Palladium in the Pd/S04/Zr02 System by Diffuse-Reflectance IR Spectroscopy. Russian Chemical Bulletin, Vol.47, No.l, Ganuary 1998), pp. 55-59, ISSN 1066-5285... 

Infrared (IR) spectroscopy is often used for the identification of surface species. Transmission IR spectroscopy is often used for studies on supported metal catalysts where the large metallic surface area allows a high concentration of adsorbed species to be examined. For powdered sample, diffuse reflectance IR spectroscopy is also used. In this experiment, the diffusely scattered IR radiation from a sample is collected and analyzed. This modification of the IR technique can be employed with high surface area catalyst sanples which are not sufficiently transparent in the IR region. 

For example, the adsorption behavior of NO on a sol-gel derived thin film, examined by diffuse reflectance IR spectroscopy, has been reported (Fujimoto, 2000). In the measurement, a furnace with a KBr window was placed in the FT-IR spectrometer and the thin film was set on a small pan in the furnace. The pre-heated sample was exposed to a NO/He stream and, after pinging with a N2 and O2 mixture gas, the spectra were taken at the elevated temperatures. In another example, the type of acid sites (Bronsted and Lewis) on sol-gel derived tungstophosphoric acid/Zr02 catalysts was determined with a FTIR (Fourier transform) spectrometer by means of pyridine adsorption (Hemandez-Cortez, 2003). 

Another spectroscopic investigation was carried out by Borovkov et al. [103], who investigated by diffuse reflectance IR spectroscopy the vibration modes of CO adsorbed on Cu(I)-Y prepared via SSIE of NH4-Y and CuCl. The various fundamental and 1st overtone bands were compared with those observed with conventionally ion-exchanged Cu-Y, Cu-MOR and Cu-L, which were subsequently auto-reduced at 673 K in vacuum. 

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