Diffuse reflectance IR Fourier transform DRIFT

Diffuse Reflectance IR Fourier Transform (DRIFT) Spectroscopy of Air Oxidation... 

Diffuse Reflectance IR Fourier Transform Spectroscopy (DRIFTS) can be employed with high surface area catalytic samples that are not sufficiently transparent to be studied in transmission. In this technique, the diffusely scattered IR radiation from a sample is collected, refocussed, and analysed. Samples can be measured in the form of loose powders. 

Diffuse reflectance infrared Fourier transform (DRIFT) spectra are obtained when IR radiation is incident on a scattering sample at a specific angle and is reflected at all angles. The diffuse reflectance process involves transmission, scattering, and reflection [67]. The technique is used to analyze an intact lignin sample without modification [65]. To study a sample by DRIFT, the sample is either dispersed in KBr (e.g., MWL) or is analyzed directly (e.g., paper sheet) and placed at the focal point of the diffuse reflectance accessory. The scattered light from the sample is collected... 

Diffuse-reflectance IR Fourier transform spectrometry (DRIFTS) is an effective way of directly obtaining IR spectra on powdered samples with a minimum of sample preparation.In addition to saving time in sample preparation, il permits conventional IR spectral data to be gathered on samples not appreciably altered from their original stale. The widespread use of diffuse-reflectance measurements had to await the general availability of F TIR instruments in the mid-107()s because tlie intensity of radiation reflected from powders is loo low to be measured at medium resolution and adequate signal-lo-noise ratios with dispersive instruments. 

Diffuse Reflection IR Fourier Transform Spectroscopy (DRIFT)... 

Identification of the specific species of the adsorbed oxyanion as well as mode of bonding to the oxide surface is often possible using a combination of Fourier Transform Infrared (FTIR) spectroscopy, electrophoretic mobility (EM) and sorption-proton balance data. This information is required for selection of realistic surface species when using surface complexation models and prediction of oxyanion transport. Earlier, limited IR research on surface speciation was conducted under dry conditions, thus results may not correspond to those for natural systems where surface species may be hydrated. In this study we review adsorbed phosphate, carbonate, borate, selenate, selenite, and molybdate species on aluminum and iron oxides using FTIR spectroscopy in both Attenuated Total Reflectance (ATR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) modes. We present new FTIR, EM, and titration information on adsorbed arsenate and arsenite. Using these techniques we... 

Infrared spectroscopy IR and Fourier transform infrared (FTIR) spectra of humic substances show bands at 3400 cm (H bonding OFI), 2990 cm (aliphatic C-FI), 1725 cm(C = 0 of CO2H, C = 0 of ketone), 1630 cm (aromatic C = C, C = 0 of carbonyl, COO or quinone), 1450 cm (aliphatic C-H), 1400 cm - (COO ) and 1200 cm (C-O or OH of CO2H). The bands are usually broad due to overlapping of individual absorbances. While IR and FTIR provide worthwhile information about functional groups, they reveal little about the chemical structure of humic substances. FTIR and diffuse reflectance infrared Fourier transform (DRIFT) are the techniques most widely used. 

Different characterization techniques are used to get an insight into the location of transition metal ions in an aluminophosphate framework. Generally, the data on the cation location are collected with difficulty since the metal concentration is low. In this regard, it is necessary to use more than one method if a reliable conclusion is to be reached (ie, the simultaneous application of several physical techniques is recommended). The following characterization methods are commonly applied diffuse reflectance UV-vis spectroscopy (DRS), electron spin resonance (ESR), electron spin echo modulation (ESEM), infrared (IR), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies, as well as the nuclear magnetic resonance spectroscopy (NMR), Mossbauer spectroscopy and the X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption spectroscopy for fine structure (EXAFS) (167,168) and references therein). 

Two methods, diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) and standard transmittance Fourier transform IR spectroscopy (FTIR), were compared to quantitatively determine the amoimts of silicon dioxide and phosphorous pentoxide in mixed water samples. For these studies a range of concentrations of each pure compound were prepared and IR spectra obtained on them. The spectra were analyzed in the regions of 750 to 820 cm for SiOi and 950 to 1050 cm for P2O5 chosen because their respective IR absorptions have minimal overlap in these regions. Using Beer s law plot program from the instrument, a Perkin Elmer 1000, standard curves were established for each compound and used to determine the amoimts of each compoimd in mixed samples. 

Self-supporting pressed discs of the pure oxide powders are prepared for in situ characterisation studies by transmission/absorption IR spectroscopy. These samples are put onto the IR beam, in an appropriate cell allowing heating, cooling, and gas/vapour manipulation. Activation is mostly performed by outgassing at relatively high temperatures. In the case of diffuse reflectance infrared Fourier transform (DRIFT) experiments the pure catalyst powder is deposited on the sample holder, with smooth pressure, and activation is mostly performed by an inert, dry gas flow. 

DRIFTS Diffuse reflectance infrared Fourier-transform Same as IR Same as IR... 

Although acetone was a major product, it was not observed by infrared spectroscopy. Flowing helium/acetone over the catalyst at room temperature gave a prominent carbonyl band at 1723 cm 1 (not show here). In this study, a DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) cell was placed in front of a fixed reactor DRIFTS only monitored the adsorbed and gaseous species in the front end of the catalyst bed. The absence of acetone s carbonyl IR band in Figure 3 and its presence in the reactor effluent suggest the following possibilities (i) acetone formation from partial oxidation is slower than epoxidation to form PO and/or (ii) acetone is produced from a secondary reaction of PO. 

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is used to obtain spectra of powders and rough polymeric surfaces such as textiles and paper. IR radiation is focused onto the surface of the sample in a cup resulting in both specular reflectance (which directly reflects off the surface having equal angles of incidence and reflectance) and diffuse reflectance (which penetrates into the sample subsequently scattering in all angles). Special mirrors allow the specular reflectance to be minimized. 

Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT).6 When IR radiation is directed onto the surface of a solid sample, two types of energy reflectance can occur specular and diffuse. The specular component is the radiation that reflects directly off the sample surface (i.e., not absorbed by the sample). Diffuse reflectance is the radiation that penetrates into the sample and then emerges. Diffuse reflectance accessories are designed to optimize the diffuse reflected energy and suppress the specular component. The optics therefore selectively directs the scattered radiation to the IR detector. 

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. 

A number of experimental alternatives to traditional IR transmission spectroscopy are suitable for overcoming some of these complicating experimental factors. In the technique of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) (Hartauer et al. 1992 Neville et al. 1992) the sample is dispersed in a matrix of powdered alkali halide, a procedure which is less likely to lead to polymorphic transformations or loss of solvent than the more aggressive grinding necessary for mull preparation or pressure required to make a pellet (Roston et al. 1993). For these reasons, Threlfall (1995) suggests that DRIFTS should be the method of choice for the initial IR examination of polymorphs. He has also discussed the possible use of attenuated total reflection (ATR) methods in the examination of polymorphs and provided a comparison and discussion of the results obtained on sulphathiazole polymorphs from spectra run on KBr disks, Nujol mulls and ATR. 

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