Coal-Based Activated Carbons Prepared with Organometallics and Their Mesoporous Structure

The preparation of a mesoporous carbon was attempted by a steam activation of a mixture of coal and metal acetylacetonate at 900 °C. The resultant porosity of the activated carbon was influenced more by the type of acetylacetonate [Al(acac) 3, Y(acac) 3, TiO(acac) 2, or Zr(acac) 4 )] than by the rank of the coal (Miike, Taiheiyo, and Morwell). Samples obtained from TiO(acac) 2 showed a particularly high mesoporosity even at an early stage of activation, as evaluated by the BET and BJH analysis of the N 2 adsorption isotherm. To clarify the influence of TiO(acac) 2 on the mechanism of formation of a remarkable amount of mesopores, the structure of the activated carbon derived from the Ti complex was investigated by X-ray diffraction measurements and observations with a transmission electron microscope (TEM). The carbon matrix was composed of small graphite-like crystallites with mesopores and TiO 2 (rutile and brookite) particles dispersed homogeneously throughout the whole matrix. The shape of the characteristic mesopores resembled that of the TiO 2 particles. The particle size distribution determined by image analysis of a TEM photograph quantitatively shows the similarities in the average size of TiO 2 particles and pores. It is believed that the formation of mesoporosity in the activated carbon is closely related to the migration of TiO 2 from the carbon matrix.