Molybdenum carbides and carbonaceous carbons on Mo/Al-FSM16 for methane conversion

摘要

The catalytic activity of 12.0 wt.% Mo/Al-FSM16(Si/Al=30) was related to the Mo carbides and carbons during CH_4 conversion at 974 K.The material had been carburized during the temperature-programmed reaction with 20% CH_4/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-Mo_2C_(1-x),beta-Mo_2C,and eta-Mo_3C_2) and carbonaceous carbons (pyrolytic and graphitic carbons).The purging treatments of the carburized catalysts at 973 K for 1 or 2 h lowered the activity,due to a decrease in the carbonaceous carbon releases of C_2H_2,C_2H_4,CO_2,and H_2O and due to the Mo carbides changing to other forms.The CH_4 conversion was responsible for eta-Mo_3C_2 conjugation to pyrolytic carbons,which played the role of the intermediate species.The IR study revealed that CH_2 and CH_3 species were formed as the intermediates of the pyrolytic species for CH_4 formation.The pulse experiments of C_2H_4,C_2H_7,C_3H_8,and C_4H_8 showed that hydrogen was readily formed through the adfsorbed C_2H_4 and C_3H_8 species as intermediates and that benzene was formed through the adsorbed C_4H_8 species.