The adsorption and desorption isotherms of nitrogen and carbon dioxide gases were measured at different temperatures on 22 activated carbons, which were derived from various precursors with various morphologies. All samples, except two from phenol resin spheres (APT and APF), showed perfectly reversible adsorption and desorption isotherms, and gave an unique curve of Polanyi potential on CO
2 gas. On these samples the BET surface area measured by N
2 coincided with that by CO
2. On the sample APT, however, irreversible adsorption was observed on CO
2 at temperatures between 0 and-72°C and N2 only at-196°C. This suggests the trapping of these gas molecules. Its Polanyi plots for CO
2 could not be appoximated by an unique curve. The sample APF showed irreversible adsorption only on N
2 gas at-196°C. On these samples the BET surface area measured by CO
2 was much higher than that by N
2.
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