A STUDY OF ADSORPTION OF CARBON DIOXIDE BY ALUMINA USING INFRARED AND ISOTHERM MEASUREMENTS

The infrared spectra of carbon dioxide adsorbed under various conditions by κ-alumina prepared by calcination of gibbsite have been measured using an apparatus which permitted the solid to be outgassed at 1000°; in separate experiments the adsorption isotherms at 150, 200, 250, 300, and 400° and the rate of adsorption of carbon dioxide have been measured by a method using 14CO2 as tracer. Adsorption of carbon dioxide at 20° produced bands at 2365, 1652, 1460, and 1234 cm-1. By studying the effect of elevated temperature and evacuation on these bands, it has been shown that the band at 2365 cm-1 is due to physically, and the other three bands to chemically adsorbed CO2, that the 1460-cm-1 band probably arises from CO2 present in fine pores in a form resembling the CO32- ion, and that the bands at 1652 and 1234 cm-1 are from a chemisorbed bidentate carbonate ion. The isotherm measurements support these conclusions and further indicate that the process leading to the formation of the bidentate ion is much faster than that leading to the simple CO32- ion.