A DIFFUSE REFLECTANCE FOURIER-TRANSFORM INFRARED STUDY OF CARBON-DIOXIDE ADSORPTION ON SILICALITE-I

The adsorption of carbon dioxide at room temperature on large, well-defined crystals of Silicalite-I was studied by diffuse reflectance Fourier transfer infra-red spectroscopy. The zeolite samples had a mean crystal size of 180-mu-m, and a narrow particle size distribution. The results show a displacement of the 1390 cm-1 Si-O-Si stretch-bend peak on adsorption/desorption of guests in the channels. The progress of carbon dioxide adsorption was followed by the 2331 cm-1 band; adsorption of the gas on a sample which already had n-hexane as a guest in the zeolitic channels led to an initial suppression of the peaks due to the alkane, but the peaks reappeared on standing. This was interpreted as signalling the adsorption of both species within the channel system rather than on the external surface of the sample.