Penetration of sodium catalysts in activated carbon: effect on the porous structure and reactivity in air, carbon dioxide and steam

Abstract

The effect of the penetration of sodium compounds on the porous structure and reactivity of activated carbon was studied. Loadings of NaCl, NaOH or Na 2CO 3 were effected from the solid phase by heating above their melting points or from an NaOH aqueous solution. The heat treatment, addition order and solution concentration were varied; a heat-treated carbon was also used as support. The samples were structurally characterized by gas adsorption (N 2, −196 °C; CO 2, 25 °C), mercury porosimetry and helium pycnometry. The reactivity of the carbon was determined in air at 400 °C and in CO 2 and steam at 900 °C. The loading method had a marked influence on the structure of the carbon, including the porosity distribution. A better agreement was found between the specific surface area and the total pore volume than between these properties and the micropore volume. The catalytic activity was much lower for NaCl than for NaOH or Na 2CO 3. As for NaOH, the reactivity was greatly dependent on the loading method. Its variation with temperature and concentration was consistent with the ash level and the micropore volume for the gasifications in CO 2 and steam; in air, the extent of gasification seemed to be determined by the porosity distribution; the reactivity increased for samples prepared with solid NaOH with regard to those obtained using a NaOH solution. The behaviour was similar with Na 2CO 3.