In situ diffuse reflectance infrared Fourier transform spectroscopy

The experimental system consists of three sections (i) a gas metering section with interconnected 4-port and 6-port valves, (ii) a reactor section including an in-situ diffused reflectance infrared Fourier transform spectroscopy reactor (DRIFTS) connected to tubular quartz reactor, (iii) an effluent gas analysis section including a mass spectrometer or a gas chromatograph (9). 

The catalysts were characterized by N2 adsorption-desorption isotherms, thermogravimetric analysis (TGA), temperature-programmed desorption of ammonia (NH3-TPD), X-ray diffraction (XRD), Raman spectroscopy, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS). The procedures and experimental conditions have been detailed elsewhere [9]. 

Accordingly, transient kinetic techniques which are able to provide unique information on the actual state of a working catalyst within a very short period of time [13,14] were applied to this complex and unstable catalytic system. Non-steady-state and steady-state isotopic transient kinetics (NSSTK and SSITK) combined with in situ diffuse reflectance infrared Fourier transformed spectroscopy (DRIFT) and temporal analysis of product (TAP) were performed in order to analyse some of the above mentioned key steps of the aromatisation process. 

The study of the dynamics of N isotope transfer under adsorption-desorption equilibrium (NO -1- O2 + He) revealed two types of NOx complexes, and their concentrations and formation rates (depending on NO and O2 concentrations) were estimated. According to in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) data, these complexes are assigned to nitrite-nitrate (1520 cm" ) and N02 species (2130 cm" ). Note that nitrite-nitrates and N02 differ clearly in the rates of their formation. Under the reaction conditions, the concentrations of both active species drop considerably. Therefore, two parallel reaction pathways were proposed that involve both active complexes. The rates of NOx complexes interaction with methane were also calculated, and the reaction with participation of N02 species was shown to proceed about 2.5 times faster than that of nitrite-nitrate. The N02 species was determined to form at the interface between CoO clusters and acid OH groups in zeolite (or at the paired Co -OH sites). This finding agrees well with in situ DRIFTS data that indicates that the N02 formation correlates with a drop in the acid OH group band intensity. 

Cycloaddition of CO2 with A -substituted phenylaziridines can be promoted by l,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) functionalized MCM-41 (MCM-41-lPr) [172]. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that MCM-41-IPr was able to capture CO2 reversibly to give an MCM-41-IPr-C02 adduct. 

Chafik T, Kameoka S, Ukisu Y, et al. In situ diffuse reflectance infrared Fourier transform spectroscopy study of surface species involved in NOx reduction by ethanol over alumina supported silver catalyst. J Mol Catal A Chem. 1998 136 203-11. 

The two examples below demonstrate further developments in SSITKA for investigating heterogeneous reactions. The group of Burch and Meunier at Queen s University Belfast developed a set-up combining in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and on-line mass spectrometry (MS) with... 

The heterogenization of MAO-activated Nd(z 3-C3H5)3 dioxane on MAO-functionalized Si(>2 was reported by T. Riihmer et al. [307]. In situ DRIFT (= diffuse reflectance infrared Fourier transform) spectroscopy and TPRS (= temperature-programmed reaction spectroscopy) were employed... 

High quality IR spectra of different carbon surfaces were obtained by photo-thermal beam deflection spectroscopy (IR-PBDS) [123,124]. This technique was developed with the intention of providing an IR technique that could be used to study the surface properties of materials that are difficult or impossible to examine by conventional means. Recently, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has been successfully applied to study the effect of different pretreatments on the surface functional groups of carbon materials [101,125-128]. Several studies aiming to improve the characterization of the carbon electrode surface and the electrode-electrolyte interface have been carried out using various in situ IR techniques [14,128-132]. The development of in situ spec-troelectrochemical methods has made it possible to detect changes in the surface oxides in electrolyte solutions during electrochemical actions. 

Direct, in situ HPTLC-FTIR measurement is carried out by diffuse reflectance using a DRIFT (Diffuse Reflection Infrared Fourier Transform Spectroscopy) unit (Fig. 15) (40-45). It is necessary to take account of the fact that at wavelengths where the absorption is large and the refractive index is high, the incident radiation is almost 100% normally reflected at the surface so that there is scarcely any diffuse reflection, which is that part of the reflection that contains the spectral information concerning the sample, in contrast to the normal (Fresnel) reflection. This means that reflectance minima and not the expected reflectance maxima are obtained at wavelengths of strong absorption. With silica gel, the absorption maxima, also known as residual radiation bands, dominate appreciably in the 1300-... 

Infrared spectrometers also enable the use of accessories for more specific purposes, such as attenuated total reflectance (ATR) used, for example, to analyze aqueous solutions that are incompatible with the material of the commercial cell windows and diffuse reflectance infrared fourier transform spectroscopy (DRIFTS), which enables in situ analyses to be performed. 

Dossi et al. [61] loaded platinum in KL zeolite by vapor deposition of Pt(hfa)2 (hfa hexafluoroacetylacetonate). The organometallic precursor was sublimated at 70 °C in a flow of argon and adsorbed on the dehydrated KL zeolite. The decomposition of Pt(hfa)2 was achieved at 350°C in a H2-atmosphere. In situ EXAFS measurements suggested the formation of small clusters (Pt-Pt coordination number of 5), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements using CO as the probe molecule indicated the formation of carbonyl clusters of the general formula [Pt3(CO)g]n (n= 1 -4). 

In fresh conditions the catalyst was analyzed by diffuse reflectance infrared Fourier transform (DRIFT-) spectroscopy to determine the NO adsorption state. The DRIFT spectra were measured in the wavelength range of 1500-2300 cm l on a Bruker IFS 88 spectrometer equipped with a Spectra-Tech in situ cell. The spectra resolution was 2 cm T The spectra were recorded in situ at 225°C in flowing 2% NO in Helium (50 cm /min) after preconditioning for 0.5 h at 400°C in hydrogen (50 cm /min). 

Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has been proven to be an excellent means of characterizing coals and related materials. This report is devoted to the evaluation of the technique as a method for situ monitoring of the chemical structural changes wrought in reactions of coal with fluid phases. This technique does not require a supporting medium (matrix) which can contain chemical artifacts which inherently serve as a barrier for access to the solid coal. The rapid response of the Fourier transform infrared technique is further beneficial for kinetic studies related to combustion, liquefaction, gasification, pyrolyses, etc. Experimental equipment and techniques are described for studies over wide ranges of pressure (10 5 Pa to ca 1.5 x 10 kPa) and temperature (298 K to 800 K). 

Our intention in this report is to demonstrate the utility of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy for coal analysis, particularly in relation to monitoring the in situ oxidation of coal, and to compare its relative merits to those of the KBr pellet and PA sampling techniques. 

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. 

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. 

Both chemical and physical processes take place during calcination and activation. Ligand decomposition from the metal complex can be monitored with in situ vibrational spectroscopy, for example, using diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). In the case of a transition metal ion, the metal oxidation state can be tracked as a function of time and temperature using in situ UV-vis spectroscopy. Finally, the formation of metal clusters and nanoparticles can be monitored using XRD, similar to that described for the synthesis of silicalite-1. 

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