Transmission infrared spectroscopy, sample

Several forms of infrared spectroscopy are in use, as illustrated in Fig. 8.4. The most common form of the technique is transmission infrared spectroscopy. In this case the sample consists typically of 10-100 mg of catalyst, pressed into a self-supporting disk of approximately 1 cm2 and a few tenths of a millimeter in thickness. Transmission IR can be applied if the bulk of the catalyst absorbs weakly. This is usually the... 

Ballinger, T.H., Wong, J.C.S., and Yates, J.T., Jr. (1992) Transmission infrared spectroscopy of high area solid surfaces. A usefid method for sample preparation. Langmuir, 8, 1575-1578. 

The present-day literature contains many more spectra obtained from singlecrystal metal surfaces by VEELS than by RAIRS. However, the much higher resolution available from the more recently developed RAIRS technique and its capability of operating in the presence of a gas phase suggest that it will contribute increasingly important information in the hydrocarbon adsorption field. The three spectroscopic techniques discussed above are much the most important ones in this area, with transmission infrared spectroscopy as the predominantly useful one for work with finely divided samples. A few other vibrational spectroscopic techniques (25) have provided information on adsorbed hydrocarbons, but are at present of more limited or specialized applications. Their principal characteristics are more briefly summarized below. 

In the limited space available this paper has attempted to give an overview of the ways that transmission infrared spectroscopy has been applied to the study of high surface area materials. Developments in improved sample preparation and the use of isotopic substitution have been discussed. The more quantitative aspect of work accomplished in the last decade has been emphasized by giving examples of adsorbtion isotherms on individual sites and the subsequent reactivity of the adsorbed molecules with these sites. 

There are three general methods available for examining solid samples in transmission infrared spectroscopy, i.e, the use of alkali halide discs, mulls or films. Your choice of method depends very much on the nature of the sample to be examined. 

A direct comparison of the spatial resolution of XPS and transmission infrared spectroscopy imaging on heterogeneous polymer blends of poly(vinyl chloride)/PMMA was presented by Artyushkova et al. [226] The spatial resolution of the XPS and infrared instruments was 2-3 p,m and 7 p.m, respectively. The comparable resolution of the instrumentation allowed for images and spectra from the same areas of the samples to be directly compared (Fig. 32). 

Transmission Fourier Transform Infrared Spectroscopy. The most straightforward method for the acquisition of in spectra of surface layers is standard transmission spectroscopy (35,36). This approach can only be used for samples which are partially in transparent or which can be diluted with an in transparent medium such as KBr and pressed into a transmissive pellet. The extent to which the in spectral region (typically ca 600 4000 cm ) is available for study depends on the in absorption characteristics of the soHd support material. Transmission ftir spectroscopy is most often used to study surface species on metal oxides. These soHds leave reasonably large spectral windows within which the spectral behavior of the surface species can be viewed. 

Infrared spectroscopy/microscopy certainly is the primary method of choice when organic substances have to be identified. Sample preparation usually is simple for identification purposes, but will be an issue for imaging experiments, and spatial resolution may then well be only in the range of a few micrometers, depending on the used experimental approach (transmission, ATR). 

In some techniques, including XRD, some IR spectroscopic techniques, and neutron activation, the surface of the soil sample is analyzed using radiation reflected or emitted from the sample. In the other types of spectroscopy, such as NMR, information is obtained from radiation passing through the sample. Infrared spectroscopy (both NIR and MIR) can be used in both transmission and reflection analyses. 

InfraRed Spectroscopy (IR). Infrared speetroscopy is an efifeetive method for eharaeterization of polymers as to ehemieal structure. IR speetra of the sample examined are obtained by two basie types of IR spectrometers dispersive or Fourier transform (FTIR) ones. Infrared spectra are usually presented as a dependence of absorption (in pereent transmission) on wave length or wave... 

The basal spacing (d 001) (DRX-Kristalloflex-805 Siemens) and the surface area (Micromeritics ASAP 2400) was obtained on the solids calcined at different temperatures. X-Ray diffraction patterns have also been obtained after ethylenglycol saturation of selected samples. High resolution transmission electron microscopy (HREM) was performed (Jeol 100 CX Temscan) on ultrathin preparations (LKB Ultratome type 8802A). TPD (NH3) and infrared spectroscopy (pyridine) allowed to evaluate the acid properties of the solid calcined at 4(X) and 600°C. 

Recently, we reported that an Fe supported zeolite (FeHY-1) shows high activity for acidic reactions such as toluene disproportionation and resid hydrocracking in the presence of H2S [1,2]. Investigations using electron spin resonance (ESR), Fourier transform infrared spectroscopy (FT-IR), MiJssbauer and transmission electron microscopy (TEM) revealed that superfine ferric oxide cluster interacts with the zeolite framework in the super-cage of Y-type zeolites [3,4]. Furthermore, we reported change in physicochemical properties and catalytic activities for toluene disproportionation during the sample preparation period[5]. It was revealed that the activation of the catalyst was closely related with interaction between the iron cluster and the zeolite framework. In this work, we will report the effect of preparation conditions on the physicochemical properties and activity for toluene disproportionation in the presence of 82. ... 

At infrared wavelengths extinction by the MgO particles of Fig. 11.2, including those with radius 1 jam, which can be made by grinding, is dominated by absorption. This is why the KBr pellet technique is commonly used for infrared absorption spectroscopy of powders. A small amount of the sample dispersed in KBr powder is pressed into a pellet, the transmission spectrum of which is readily obtained. Because extinction is dominated by absorption, this transmission spectrum should follow the undulations of the intrinsic absorption spectrum—but not always. Comparison of Figs. 10.1 and 11.2 reveals an interesting discrepancy calculated peak extinction occurs at 0.075 eV, whereas absorption in bulk MgO peaks at the transverse optic mode frequency, which is about 0.05 eV. This is a large discrepancy in light of the precision of modern infrared spectroscopy and could cause serious error if the extinction peak were assumed to lie at the position of a bulk absorption band. This is the first instance we have encountered where the properties of small particles deviate appreciably from those of the bulk solid. It is the result of surface mode excitation, which is such a dominant effect in small particles of some solids that we have devoted Chapter 12 to its fuller discussion. 

Infrared spectroscopy is a relatively simple technique, nondestructive, and versatile enough to analyze solids, liquids, and gases with a minimum of sample preparation. Polymers can be mixed with potassium bromide and then pressed into pellets. Films can be prepared from melt or cast from solution and can be studied easily. In bulk samples or powders, or if a concentration profile is needed, the reflectance technique is probably more suitable than transmission. 

All of the usual sampling techniques used in infrared spectroscopy can be used with FT-IR instrumentation. The optics of the sampling chamber of commercial FT-IR instruments are the same as the traditional dispersive instruments so the accessories can be used without modification for the most part. To make full use of the larger aperature of the FT-IR instrument, some accessories should be modified to accomodate the larger beam. The instrumental advantages of FT-IR allow one to use a number of sampling techniques which are not effective using dispersive instrumentation. Transmission, diffuse reflectance and internal reflectance techniques are most often used in the study of epoxy resins. 

Infrared spectroscopy. IR spectra were recorded on a Nicolet 5DX FT-IR spectrometer. A thin coating of the condensed silanes was applied on KBr pellets made from a very high purity KBr powder (J. T. Baker Chemical Co.). The spectra of these pellets were recorded using the transmission method. Liquid silanes were analyzed using the internal reflection attachment (IRA). The number of scans was chosen to be 20 for both background and samples. 

Conventionally, infrared spectroscopy is carried out in the transmission mode, where the light passes through a sample cell with a defined thickness. There are two main disadvantages of this technique for the purpose of reaction analysis. 

There are several major areas of interfacial phenomena to which infrared spectroscopy has been applied that are not treated extensively in this volume. Most of these areas have established bodies of literature of their own. In many of these areas, the replacement of dispersive spectrometers by FT instruments has resulted in continued improvement in sensitivity, and in the interpretation of phenomena at the molecular level. Among these areas are the characterization of polymer surfaces with ATR (127-129) and diffuse reflectance (130) sampling techniques transmission IR studies of the surfaces of powdered samples with adsorbed gases (131-136) alumina(137.138). silica (139). and catalyst (140) surfaces diffuse reflectance studies of organo- modified mineral and glass fiber surfaces (141-143) metal overlayer enhanced ATR (144) and spectroelectrochemistry (145-149). 

Infrared spectroscopy of adsorbed CO is a useful characterization tool for dendrimer-templated supported nanoparticles, because it directly probes particle surface features. In these experiments, which are performed in a standard infrared spectrometer using an in-situ transmission or DRIFTS cell, a sample of supported DENs is first treated to remove the organic dendrimer. Samples are often reduced under H2 at elevated temperature, flushed with He, and cooled to room temperature. Dosing with CO followed by flushing to remove the gas-phase CO allows for the spectrum of surface-bound CO to be collected and evaluated. Because adsorbed CO stretching frequencies are sensitive to surface geometric and electronic effects, it is potentially possible to evaluate the relative effects of each on nanoparticle properties. 

Characterization of the catalyst acid sites by infrared spectroscopy correlated well with the results of ammonia desorption experiments. The transmission spectra of HZSM-5 (Figure 2a), and SAPO-34 (Figure 2b) following in vacuo pretreatment at 650 K all showed absorbance bands near 3610 cm. Since these two molecular sieves were the only samples to show high-temperature NH3 desorption peaks... 

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