Abstract Three coking coals were pyrolysed in the presence of the Lewis acid MoCl 5 under an inert atmosphere at a final temperature of 750°C, the ultimate aim of this work being the elaboration of active carbon supported catalysts for use in hydrodenitrogenation reactions. The values of the parameters characterizing the porous structure of the chars before and after steam activation were determined using CO 2 and C 6H 6 sorption measurements at 25°C. Char from the lowest rank coal had the most developed ultramicroporosity (pore width <0.4 nm) and the presence of MoCl 5 in the precursor does not seem to exert much influence. In the case of the higher rank coals, a significant development of the ultramicroporosity was observed in the molybdenum enriched chars before activation and their reactivity toward steam was increased. After steam activation, the structure of the activated chars was mainly microporous, but a significant development of the mesoporosity was observed.