Discs, sample self-supporting

The FT-IR measurements were carried out in a Nicolet IRTF spectrometer. Samples (self-supported discs) were activated in situ under vacuum (10 6 mbar) at 450°C before adsorption of probe molecules. Adsorption was carried out at room temperature the physisorbed species were removed at RT (C02) and 150°C (2,6-dimethylpyridine) under vacuum. 

FTIR spectra were collected with a Nicolet 740 spectrometer and a custom built in situ gas flow cell. The spectrometer was equipped with a MCT-B detector cooled by liquid nitrogen. Approximately 15 mg of the MgO catalyst sample was pressed into a self-supported disc and placed in a sample holder located at the center of the cell. The temperature in the cell was measured with a thermocouple placed close to the catalyst sample. Transmission spectra were collected in a single beam mode with a resolution of 2 cm 1. Prior to introduction... 

The ESR measurements were conducted after evacuation of the catalysts at various temperatures (RT to 723 K) and after NO adsorption at RT. ESR spectra were recorded at 77 K on a RADIOPAN SE/X 2547 spectrometer. The patterns were obtained at vESR = 8.9 GHz FTIR study was performed using a VECTOR 22 (BRUKER) spectrometer The self supported discs of 10 mg cm 2 of the catalysts were activated under vacuum at 723 K Pyridine was admitted at RT and after saturation the samples were degassed at RT, 423, 523, and 623 K in vacuum for 30 min. 

FTIR spectra of the self-supported zeolite discs were collected at a resolution of 2 cm 1 using a Nicolet Magna 550 FTIR spectrometer. Pyridine was used as a probe molecule to characterise Broensted and Lewis acid sites. Prior to all FTIR experiments the samples were activated under vacuum at 400°C for 16 h. The detailed experimental procedure is described elsewhere.12 The IR spectra of the reduced samples were collected at ambient temperature after reduction of the catalysts by hydrogen at 500°C (Ph2 = 50 torr, duration of treatment = 1 h). 

For IR measurements, the sample was pressed into self-supporting discs ( 10 mg.cm ). The spectra of the adsorbed species were obtained by subtracting tire spectrum of the wafer from the spectrum obtained after adsorption. 

In industry, time is at premium so the emphasis is always to carry out the analysis in the most efficient manner possible. In practice, this means that the analyst employs the sampling method that requires the least possible sample preparation. Historically, the great majority of liquid samples were run as thin Aims between infrared transparent plates (usually KBr) or in fixed pathlength cells. Similarly, most solid samples were run as KBr discs, as mulls or as a thin film deposited from solution onto a suitable substrate. Polymers were usually hot-pressed to make a self-supporting film, with a thickness typically between 0.020 and 1.0 mm the former being used for the identification of a bulk material and the latter for the identification of minor components, contaminants, or degradation products. 

The most common means of recording the spectrum of solid samples, the pressed halide disc method, relies on containing the material to be analysed in a self-supporting matrix of infrared transparent material. KBr is by far the most popular salt to use, although other metal halides, such as Csl or KCl, have their own particular advantages. Csl, for instance, transmits down to 180 cm whereas KBr cuts off at 350 cm ... 

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. 

The in situ characterization of a solid surface by FT-IR is a well known and current method of investigation in a number of laboratories. Nevertheless, each team of scientists may use different analysis techniques. In our case we choose the transmission technique, so that samples are pressed (10 Pa) into self-supported discs (2cm area, 7-lOmg cm ). They are placed in a home-made quartz cell equipped with KBr windows (Figure 4.5). 

Another procedure for dealing with samples insoluble in counting solution is to support them on a medium such as paper strips, filter discs, glass fibre or DEAE cellulose prior to adding them to a counting vial [235-237]. As indicated earlier, use of this has been in chromatography where the spot has been cut out of the paper or scraped from the plate. Although useful for materials insoluble in scintillator fluid, self-absorption for tritiated samples may constitute a major drawback in this technique, just as it does for the suspension methods. It should be evident why the recent developments in in combustion procedures are so important in the problem of sample preparation. 

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