Nonoxidative methane activation, coupling, and conversion to ethane, ethylene, and hydrogen over Fe/HZSM-5, Mo/HZSM-5, and Fe-Mo/HZSM-5 catalysts in packed bed reactor

A high abundance of methane and its relatively low price make it an attractive raw feedstock for the production of ethylene, which is in the consumer demand in recent years. Direct catalytic nonoxidative conversion is interesting, because it could be utilized on natural gas well sites. Monometallic and bimetallic Fe and Mo catalysts were prepared for the purpose of the coupling to ethane and ethene. Three supported materials were synthesized with the following loading of metal: 2.5-wt% Fe, 5.0-wt% Fe, and 2.5-wt% Mo on HZSM-5. Process' chemical reactions were also catalyzed with a constant 2.5-wt% Mo/HZSM-5, which had different amounts of Fe, namely, 0.5, 1.0, and 2.5 wt%. Fourier transform infrared (FTIR), N-2 adsorption/desorption, NH3 temperature-programmed desorption (TPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were applied for characterization. Coke, accumulated on spent solids, was determined by thermogravimetric analysis (TGA). Activity was evaluated in quartz-packed bed reactor. All surfaces suffered from deactivation due to carbon formation. The addition of Fe to Mo increased CH4 reacted. The highest selectivity for alkenes was achieved over 1.0-wt% Fe to 2.5-wt% Mo/HZSM-5. At the peak of performance, the C-based reactivity was 52% for olefins and 2% for alkanes. Stability was accomplished over 2.5-wt% Fe/HZSM-5, where the rate of C-2 synthesis was comparatively stable for 20 hours of the time on stream. The selective C-basis yield for C2H4 and C2H6 was 36% and 23%, respectively. The lowest measured quantity of (carbonaceous) by-products was deposited on 2.5-wt% Fe/HZSM-5 after 26 hours. Propylene was detected very limitedly.