High-pressure diffuse reflectance infrared

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. 

Vibrational spectroscopy is the method of choice for the characterizing functional groups in complex organic molecules. Infrared transmission spectroscopy has been used on dried humics pressed into KBr pellets to determine the relative carboxylate content of humic materials (14-16). However, interferences arise from the presence of water bands and possible alterations of the samples under the high pressures used to form the pellets. Diffuse-reflectance techniques can avoid some of the difficulties associated with the KBr pressed-pellet method (9,17-18). To obtain a spectrum analogous to an absorption spectrum, the data are transformed from reflectance units to Kebulka-Munk (K-M) units. However, K-M units are related to... 

Clarke, F. J. J., and Larkin, J. A. (1985). Emissivity determined from hemispherical reflectance and transmittance throughout the thermal infrared spectrum. High Temperatures-High Pressures 17, 89. Description of new method of mid-IR diffuse measurements leading to mid-IR diffuse standards. 

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