IR cells

Another variation In IR cell design which we have developed Is shown In Figure 1. In this cell, three surface measurement objectives are readily achieved ... 

The catalyst for the in situ FTIR-transmission measurements was pressed into a self-supporting wafer (diameter 3 cm, weight 10 mg). The wafer was placed at the center of the quartz-made IR cell which was equipped with two NaCl windows. The NaCI window s were cooled with water flow, thus the catalyst could be heated to 1000 K in the cell. A thermocouple was set close to the sample wafer to detect the temperature of the catalyst. The cell was connected to a closed-gas-circulation system which was linked to a vacuum line. The gases used for adsorption and reaction experiments were O, (99.95%), 0, (isotope purity, 97.5%), H2 (99.999%), CH4 (99.99%) and CD4 (isotope purity, 99.9%). For the reaction, the gases were circulated by a circulation pump and the products w ere removed by using an appropriate cold trap (e.g. dry-ice ethanol trap). The IR measurements were carried out with a JASCO FT/IR-7000 sprectrometer. Most of the spectra were recorded w ith 4 cm resolution and 50 scans. 

Catalytic combustion experiments have been performed in a flow reactor operating below the lower explosion limits using HC/02/He mixtures. The product analysis was done by gas chromatography. FT-IR spectra have been recorded with a Nicolet Magna 750 instrument, using conventional IR cells connected with evacuation-gas manipulation apparatus. The powder was pressed into self-supporting disks, calcined in air at 773 K and outgassed at 773 K for 20 minutes before experiments. 

FT-IR spectra were recorded at RT on a Perkin-Elmer 1760-X spectrophotometer equipped with a cryodetector, at a resolution of 2 cm-" (number of scans -100). In the 1070-960 cm- region, band integration and curve fitting were carried out by Curve fit, in Spectra Calc. (Galactic Industries Co.). Powdered materials were pelleted in self-supporting discs of 25-50 mg cm-2 and 0.1-0.2 mm thick, placed in an IR cell allowing thermal treatments in vacuo or in a controlled atmosphere. 

Other authors also determined by FTIR that organic nitrocompounds are formed as primary products of the NO CH4-SCR reaction on ZSM-5-based catalysts [121-124], They preadsorbed nitromethane on the sample placed in the IR cell and followed by IR its transformation into other intermediates under 02 and NO versus time at different temperatures. For Cu- and Co-ZSM-5, it was shown that around 300°C adsorbed nitromethane is easily converted into isocyanates and then melamine via polymerization of the former species. Both species easily interact with molecular oxygen, while no reaction with NO is observed and the reactivity depends on the temperature and the nature of the transition metal cation. 

Catalyst Activation Gas phase activation of supported DENs was examined using in-situ FTIR spectroscopy and FTIR spectroscopy of adsorbed CO. For in-situ dendrimer decomposition studies, the spectra were collected under a gas flow composed of 20% 02/He or 20% H2/He. The supported DEN sample was pressed into a self-supporting wafer, loaded into a controlled atmosphere IR cell, and collected as the sample background. The temperature was raised stepwise and spectra were collected at each temperature until little or no change was observed. After oxidation, the sample was reduced in 20% H2/He flow with various time/temperature combinations. The sample was then flushed with He for lhr at the reduction temperature. After cooling under He flow, a background spectrum was collected at room temperature. A 5% CO/He mixture was flowed over the sample for 15 minutes, followed by pure He. IR spectra of CO adsorbed on the catalyst surface were collected after the gas phase CO had been purged from the cell. 

One cm3 of the reactant/product/catalyst mixture was sampled periodically during the reaction for the transmission infrared analysis (Nicolet Magna 550 Series II infrared spectrometer with a MCT detector). The concentrations of reactants and products were obtained by multiplying integrated absorbance of each species by its molar extinction coefficient. The molar extinction coefficient was determined from the slope of a calibration curve, a plot of the peak area versus the number of moles of the reagent in the IR cell. The reaction on each catalyst was repeated and the relative error for the carbamate yield measured by IR is within 5%. 

In our laboratory, ECD spectra provide important auxiliary data for the proteins and peptides we study. ECD spectra are usually obtained for more dilute samples using strain-free quartz cells having various sample path lengths from 0.2 to 10 mm for concentrations of 0.1-1 mg/ml. To test if concentration effects cause a difference in the interpretation of data from the two techniques, which can be very important for study of unfolded proteins and peptides, we also can use IR cells and samples directly in the ECD spectrometer (Baumruk et al., 1994 Yoder, 1997 Yoder et al., 1997b Silva et al., 2000b). 

Infrared transmission spectra were measured on self supported wafers (2 cm2, 20 mg), in a quartz IR cell allowing sample heating under vacuum and introduction of standardised volumes of gas. The samples were activated under vacuum (106 torr) by heating (1 K.min 1) up to 673 K. 

The zeolite was pressed into thin pellet and activated in situ in IR cell in vacuum at 800 K for 1 h. The IR spectra were recorded with a Broker Equinox 55 spectrometer (equipped with an MCT detector) with the spectral resolution 2 cm 1. 

Continuous generation simply means that the intermediate is continuously replenished by some method and examined under pseudoequilibrium conditions. For instance, Whyman (4) was able, using a special IR cell working at high pressure and temperature, to monitor the behavior of several species of importance in the thermal hydro formyl at ion catalytic cycle. Similarly, Koemer von Gustorf and colleagues (5) have monitored the photochemical... 

Window insulation, noble gases in, 17 378 Window material, in ir cells, 14 228-229 Windows... 

Reaction of a Pt (II) carbonyl derivative with halide from the IR cell window monitored by v(CO)... 

What defines the pathlength in a sealed demountable IR cell ... 

Describe the pressure-vacuum method of filling an IR cell equipped with inlet and outlet ports. 

Both the GC-MS and GC-IR instruments obviously require that the column effluent be fed into the spectrometer detection path. For the IR instrument, this means that the IR cell, often referred to as a light pipe, be situated just outside the interferometer (Chapter 8) in the path of the light, of course, but it must also have a connection to the GC column and an exit tube where the sample may possibly be collected. The infrared detector is nondestructive. With the mass spectrometer detector, we have the problem of the low pressure of the mass spectrometry unit coupled with the ambient pressure of the GC column outlet. A special method is used to eliminate carrier gas while retaining sufficient amounts of the mixture components so that they are measurable with the mass spectrometer. 

IR-cell can be used as an on-line detector connected to a reaction vessel. Both techniques play an important role in the study of the variation of the ligand environment of the catalytic complexes in a controlled manner. Both IR and NMR spectroscopy can be used at high pressure in dedicated tubes or cells. The specific advantages and disadvantages of both techniques are summarised below ... 

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