Pellets self-supporting pellet technique

The most common method for preparing samples for pretreatment and subsequent measurement of IR spectra is the self-supporting pellet technique. In this... 

Analysed in the form of a self-supported pellet. Pure pellets are produced by pressing a mass of 6 to 20 mg, chosen to give a sample which is transparent in a given spectral domain. This type of technique is routinely used for the in situ study of catalysts. When the sample is too absorbent, even for pellet weights of the order of 6 to 7 mg, another method is used in which the sample is deposited via friction on a KBr plate. This technique only allows approximately 0.5 to 4 mg of product to be deposited and may result in detection problems. 

To minimize this problem, self-supporting pellets are usually prepared, and the minimum pressure required to form a mechanically stable pellet is used. Although much information related to surface acidity has been obtained with transmission techniques, there remains some question regarding the extent of surface alteration due to sampling procedures. 

For characterization we used IR and ESR spectroscopy. ESR spectra were recorded on a JE0L-FE-3X type spectrometer in the X-band using Mn in MgO matrix for field calibration. For IR studies KBr pellet and self-supporting wafer techniques were utilized. Adsorption of N2 and solid-gas (O2, H2) interactionE were investigated in a high vacuum equipment supplemented with MS gas analysis. 

InSect. 5.2.2.10, the work by Kubelkovaetal. [271] onH-Y, Ce,Na-Y and dealuminated Ce, Na-Y was already mentioned, which was carried out employing the DRS/KBr pellet technique. These authors, however, obtained also DRS spectra of the powdered materials and compared their results with those of the conventional IR transmission spectroscopy of self-supporting wafers. They found that some of the OH bands observed by DRS were shifted to lower wavenumbers and attributed this effect to the higher temperature produced by the DRS beam in the powdered samples. In an investigation of hydrothermally treated and, thus, dealuminated H-ZSM-5 Martin et al. [429] observed by the pyridine/IR technique an elimination of Bronsted sites accompanied by a condensation of extra-frame-work Al-containing species (Lewis centers). 

---