Effect of steam and carbon dioxide activation in the micropore size distribution of activated carbon

This work presents the different effects of steam and carbon dioxide activation of a char in both the development of microporosity and the micropore size distribution using immersion microcalorimetry of liquids with different molecular size (benzene, 2,2 dimethylbutane, iso-octane and cr-pinene). The study has been carried out with three series of carbons, two of them prepared by steam activation and the third one by carbon dioxide activation, covering a wide range of burn-off (8-70%). The experimental results show that carbon dioxide activation mainly causes the creation of microporosity. However, steam activation widens the microporosity as from the early stages of the activation process, the resulting activated carbons exhibiting a lower micropore volume. The different porous structures produced by both activating agents is related to the oxygen surface groups in the carbon, as measured by temperature programmed desorption (TPD). Activation by carbon dioxide creates not only a larger number of groups evolving as CO but also these groups are thermally more stable than those produced by steam activation. Copyright (C) 1996 Elsevier Science Ltd