Abstract
Activated carbons (AC) and activated carbon fibres (ACF) with different surface chemistry and porosity have been studied to analyse the SO 2 retention in presence of O 2 at room temperature. Samples surface chemistry was studied using temperature programmed desorption (TPD) and H 2 temperature programmed reaction experiments. The porous texture was determined by CO 2 and N 2 adsorption isotherms at 273 K and 77 K, respectively. SO 2 adsorption experiments were performed at 313 K on fresh and heat treated (N 2 1173 K) samples using gas mixtures of 2000 ppm SO 2 in N 2 or 2000 ppm SO 2/5% O 2 in N 2. Adsorption experiments on heat treated samples show that the presence of surface oxygen complexes impedes the SO 2 adsorption and its oxidation to SO 3. Additionally, no correlation has been found between the amount of SO 2 adsorbed and the number of active sites created by the evolution of oxygen complexes during heat treatment. The results obtained have been explained using the fundamentals of gas adsorption for microporous solids. The SO 2 uptake is analyzed considering the SO 2 oxidation to SO 3 as a new variable that is strongly affected by the pore size distribution. An optimum pore size exists (i.e. pore size of about 7Å)in which the oxidation of SO 2 to SO 3 is favoured. A pore width enlargement decreases the conversion of SO 2 to SO 3 and, thus, the total amount of SO 2 retained by the carbon sample.
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