Diffuse reflectance infrared spectra

Diffuse reflectance infrared spectra were acquired for the sorbitol samples. As shown in Figure 7, identical IR spectra were observed for all materials. The IR spectral band assignments are presented in Table 9, and the measured absorbance bands are consistent with the structure of sorbitol. 

Fig. 8.8 Diffuse reflectance infrared spectra of an MgO-supported mononuclear gold compound, dimethyl gold acetyl acetonate, along with spectra of several reference compounds in the O—H and C—H stretch and the fingerprint region. Detailed assignments are shown in Table 8.3. (Adapted from [29]).

Isolation of two trimeric compounds with lactone ring. Holzforschung 35 183-187 Yeboah SA, Wang S-H, Griffiths PR (1984) Effect of pressure on diffuse reflectance infrared spectra of compressed powders. Appl Spectrosc 38 259-264 Zavarin E, Nguyen C, Romero E (1982) Preparation of enzymatically liberated lignin from naturally brown-rotted wood. J Wood Chem Technol 2 343-37... 

Brimmer, P.J. Griffiths, P.R. Harrick, N.J. Angular dependence of diffuse reflectance infrared spectra. I. FT-IR spec-trogoniophotometer. Appl. Spectrosc. 1986, 40, 258-265. 

Since the interaction of tt)-epoxysiIanes with oxide surfaces at elevated temperatures exclusively leads to the loss of the epoxy fiinction, additional silylation experiments were carried out under ambient conditions. Fig.4 shows some diffuse reflectance infrared spectra of the silica material In all cases, an additional absorption band around 3046 cm characteristic of the intact oxirane fragment is detected. 

Nanzyo, M., Diffuse reflectance infrared spectra of phosphate sorbed on alumina gel, J. Soil Sci., 35, 63, 1984. 

T emperature-programmed desorption (TPD) of ammonia and infrared spectroscopy (IR) of adsorbed pyridine are probably the most extensively used methods for characterising acidity (number, strength and nature of acid sites) in zeolites [17,18]. Fig. 1 shows the diffuse-reflectance infrared spectra of pyridine adsorbed on H-Y, H-Y(d5o%) and H-Y(d64%) samples at... 

Figure 2. Transmission and diffuse reflectance Infrared spectra of a clear melamine formaldehyde crossllnked acrylic copolymer coating.

Fig. 47. Diffuse reflectance infrared spectra (DRIFT) of hydrogen adsorbed on H-ZSM-5 at 77 K a, b, c after heat-pretreatment in high vacuum at 770,970 and 1220 K, respectively spectrum d after deep-bed treatment at 770 K abscissa linear in wavelength important bands indicated by wavenumbers in cm" (adopted from [713])...

Diffuse reflectance, infrared, spectra of H-ZSM-5 (after Kazansky et a(. 1965) (41). 

Figure 8.6 Diffuse reflectance infrared spectra of (a) form I and (b) form II of cortisone acetate [4]. Reprinted from Spectrochim. Acta, 47A, Deeley, C. M., Spragg, R. A. and Threlfall, T. L., A comparison of Fourier transform infrared and near-infrared Fourier transform Raman spectroscopy for quantitative measurements an application in polymorphism , 1217-1223, Copyright (1991), with permission from Elsevier.

Figure 8.9 Carbonyl regions of the diffuse reflectance infrared spectra of two polymorphs of an anti-inflammatory drug (a) pol3miorph I (b) polymorph II (cf. SAQ 8.2) [5]. Reprinted from J. Pharmaceut. Biomed. Anal, 11, Roston, D. A., Walters, M. C., Rhinebarger, R. R. and Foto, L. J., Characterization of polymorphs of a new antiinflammatory drug , 293-300, Cop3night (1993), with permission from Elsevier.

Figure 8.9 Diffuse reflectance infrared spectrum of a silica support, showing silica vibrations at frequencies below 1300 cm1, overtones and combination bands between 1700 and 2050 cm-1, and various hydroxyl groups at frequencies above 3000 cm 1. The sharp peak at 3740 cm"1 is due to isolated OH groups, the band around 3550 cm 1 to paired, H-bonded OH groups, and the band around 3660 cm 1 to hydroxyls inside the silica (courtesy of R.M. van Hardeveld, Eindhoven).

Figure 13. Diffuse reflectance infrared spectrum of Ru3(C0)12 supported on A1203, prior to activation.

Figure 64. Typical diffuse reflectance infrared spectrum of a dried water-based drilling fluid. (Reproduced with permission from reference 181. Copyright 1991 Society of Petroleum Engineers.)...

Figure 8.1 Diffuse reflectance infrared spectrum of acetyl salicylic acid. From Stuart, B., Biological Applications of Infrared Spectroscopy, ACOL Series, Wiley, Chichester, UK, 1997. University of Greenwich, and reproduced by permission of the University of Greenwich.

In the diffuse reflectance mode, samples can be measured as loose powders, with the advantages that not only is the tedious preparation of wafers unnecessary but also diffusion limitations associated with tightly pressed samples are avoided. Diffuse reflectance is also the indicated technique for strongly scattering or absorbing particles. The often-used acronyms DRIFT or DRIFTS stand for diffuse reflectance infrared Fourier transform spectroscopy. The diffusely scattered radiation is collected by an ellipsoidal mirror and focussed on the detector. The infrared absorption spectrum is described the Kubelka-Munk function ... 

Persson et al. (1991) used diffuse reflection infrared Fourier transform (DRIFT) spectroscopy to study the interactions between galena, pyrite sphalerite and ethyl xanthate. They provided the evidence that the DRIFT spectrum of oxidized galena treated with an aqueous solution of potassium ethyl xanthate is practically identical with that of solid lead (II) ethyl xanthate, which can be formed as the only detectable siuface species on oxidized galena. Dialkyl dixanthogen is formed as the only siuface species in the reaction between oxidized pyrite and aqueous solution of potassium alkyl xanthate. 

Hydrated silica gel was modified with APTS (sample 1) and studied by DRIFT (Diffuse Reflectance Infrared Fourier Transform) and CP MAS NMR. The IR spectrum of the modified silica (figure 9.4) shows silane NH, CH and Si-O-Si bands along with silica lattice and surface vibrations. Assignments of IR bands of APTS modified silica are given in table 9.2. 

For some sample types, for example a coated substrate, it is not possible to collect an infrared transmission spectrum, whereas in some cases (e.g. when there are concerns over the effects of sample preparation) it may be more desirable to collect a reflected spectrum. The most popular reflection techniques nowadays are internal reflection spectroscopy (IRS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)... 

Fieure 6 Diffuse reflectance infrared Fourier transform (DRIFT-) spectrum of the platinum based catalyst measured at 225°C in flowing 2% NO in helium (50 cm /min)... 

Diffuse reflection infrared absorption (DRIFT) spectrum of cephradine dihydrate. 

Diffuse reflectance or DRIFTS (diffuse reflectance infrared Fourier-lransform spectroscopy) allows the sain)le to be analysed neat, ot diluted in a non-absorbing matrix (e.g. KCl or KBr at 1-5% w/w analyte). DRIFTS also may be used to obtain the spectrum of a solute in a volatile solvent by evaporating the solution onto KBr. When the IR radiation interacts with the powdered sample it will be absorbed, reflected and diffracted. The radiation which has been diffusely reflected contains vibrational information on the molecule. This technique allows non-destructive testing of neat materials and is suited to quantitative analysis, although care must be taken to ensure that a consistent particle size is used. 

The primary components and the chemical structure of the raw peat and the solid product were further analyzed by Fourier transform infrared spectroscopy (FTIR) 0ASCO 670 Plus) using the Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) technique and the JASCO IR Mentor Pro 6.5 software for spectral analysis. The cross polarization/magic angle spinning (CP/MAS) NMR spectrum of raw peat and the solid... 

Fig. 26.6 Diffuse reflectance infrared Fourier transform spectra for (a) freshly prepared PSi before functionalization and PSi derivatized with (b) 1-decene and (c) decylaldehyde and (d) a difference DRIFTS spectrum of (b)-(a) (Reprinted with permission from Boukherroub et al.

The scope of the present chapter will be exclusively concerned with investigations of diffuse reflectance work performed in the UV/VIS region of the spectrum, and with colors that can be perceived by the human eye. Much work has been conducted in the near-infrared region of the spectrum, but that aspect will be covered elsewhere in this book. 

Measurements of supported catalysts in diffuse reflection and transmission mode are in practice limited to frequencies above those where the support absorbs (below about 1250 cm-1). Infrared Emission Spectroscopy (IRES) offers an alternative in this case. When a material is heated to about 100 °C or higher, it emits a spectrum of infrared radiation in which all the characteristic vibrations appear as clearly recognizable peaks. Although measuring in this mode offers the attractive advantage that low frequencies such as those of metal-oxygen or sulfur-sulfur bonds are easily accessible, the technique has hardly been explored for the purpose of catalyst characterization. An in situ cell for IRES measurements and some experiments on Mo-O-S clusters of interest for hydrodesulfurization catalysts have been described by Weber etal. [11],... 

Infrared spectra of zeolitic samples can be measured in several different modes. These include transmission, diffuse reflectance, attenuated total internal reflection (ATR) and emission. Transmission and diffuse reflectance are by far the most widely used of these techniques. In the transmission mode, the sample is placed directly in the infrared beam of the instrument and the light passing through or transmitted is measured by the detector. This transmitted signal (T) is ratioed to the open beam (no sample) signal (To) to get the transmission spectrum of the sample. The transmission spectrum is converted to an absorbance spectrum ... 

A majority of traditional NIR measurements are made on solid materials and these involve reflectance measurements, notably via diffuse reflectance. Likewise, in the mid-IR not all spectral measurements involve the transmission of radiation. Such measurements include internal reflectance (also known as attenuated total reflectance, ATR), external reflectance (front surface, mirror -style or specular reflectance), bulk diffuse reflectance (less common in the mid-IR compared to NIR), and photoacoustic determinations. Photoacoustic detection has been applied to trace-level gas measurements and commercial instruments are available based on this mode of detection. It is important to note that the photoacoustic spectrum is a direct measurement of infrared absorption. While most infrared spectra are either directly or indirectly correlated... 

An infrared spectrum is a plot of percent radiation absorbed versus the frequency of the incident radiation given in wavenumbers (cm ) or in wave length ( xm). A variation of this method, diffuse reflectance spectroscopy, is used for samples with poor transmittance, e.g. cubic hematite crystals. Increased resolution and sensitivity as well as more rapid collection of data is provided by Fourier-transform-IR (FTIR), which averages a large number of spectra. Another IR technique makes use of attenuated total reflectance FTIR (ATR-FTIR) often using a cylindrical internal reflectance cell (CIR) (e.g. Tejedor-Tejedor Anderson, 1986). ATR enables wet systems and adsorbing species to be studied in situ. 

All infrared spectrometers generate data that are contained in the infrared spectrum (see Fig. 10.1). The spectrum represents the ratio of transmitted intensities with and without sample at each wavelength. This intensity ratio is called transmittance (7 ) can be replaced by percent transmission (%7 ) or by absorbance A = log(l/T). If the experiment is conducted using reflected or diffuse light, pseudo-absorbance units are used (cf. 10.10.2). Finally, it is common to report wavelengths in terms of wave number v (cm-1 or kaysers) knowing that ... 

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