The catalytic activity of 12.0 wt.% Mo/Al-FSM16 (Si/Al = 30) was related to the Mo carbides and carbonaceous carbons during CH4 conversion at 973 K. The material had been carburized during the temperature-programmed reaction with 20% CH4/H-2 at 973 K, with and without purging in He. The temperature-programmed surface reaction and X-ray diffraction analysis showed that the carburized catalysts consisted of Mo carbides (alpha-Mo2C1-x, beta-Mo2C, and eta-Mo3C2) and carbonaceous carbons (pyrolytic and graphitic carbons). The purging treatments of the carburized catalysts at 973 K for I or 2 It lowered the activity, due to a decrease in the carbonaceous carbon releases of C2H2, C2H4, CO2, and H2O and due to the Mo carbides changing to other forms. The CH4 conversion was responsible for eta-Mo3C2 conjugation to pyrolytic carbons, which played the role of the intermediate species. The IR study revealed that CH2 and CH3 species were formed as the intermediates of the pyrolytic species for CH4 formation. The pulse experiments Of C2H4, C2H6, C3H8, and C4H8 showed that hydrogen was readily formed through the adsorbed C2H4 and C3H8 species as intermediates and that benzene was formed through the adsorbed C4H8 species. (C) 2003 Elsevier B.V. All rights reserved.