Synthesis and Characterization of Hierarchical Co/ZSM-5 as Catalyst for Methane Partial Oxidation

摘要

Hierarchical ZSM-5 zeolite was synthesized using small tetrapropylammonium hydroxide molecule and cationic polymer polydiallyl-dimethylammonium chloride as templates, sodium alumina and tetra ethyl ortho silicate. XRD pattern of the zeolite and SEM images indicate that the synthesis was successful to form ZSM-5 structure, and EDS measurement confirmed that the Si/Al ratio in the structure was 32. FTIR measurement showed that the template was completely removed after the zeolite was calcined at 550 ℃ leaving mixed of micropores and meso-channels in the structure. Specific surface area of this material is 438 m~2 /g and pore size distribution is the highest at 18 The Barrett–Joyner– Halenda analysis showed the formation of micro- and meso-sized pores. Co/ZSM5 was then prepared by impregnating cobalt ions (2.5% wt zeolite) in the as-synthesized hierarchical ZSM-5, in order to obtained heterogeneous catalyst for partial oxidation of methane gas to methanol and formaldehyde. Before reaction, Co-ZSM-5 was calcined at 550 ℃ for 3 h in flow of O_2 (200 mL/min), then flushed with nitrogen at RT. The catalytic test was performed at 150 ℃ for 30 min in a batch reactor consisting of methane, N_2 (CH_4:N_2 ratio is 0.5:2) and Co/ZSM5 catalyst (2.5% wt). The reaction products were collected by extraction with ethanol and analyzed using GC-FID. Current results show that the partial oxidation of methane tends to methanol production, indicating that the reaction is preferable to take place in the meso-channels rather than in the surface of micropore structure. This result confirms that partial oxidation of methane could be directed to methanol formation by using mesoporous ZSM-5 as catalyst. This information could help to decide the type of ZSM-5 catalyst used to convert methane, i.e. biogas from landfill or livestock, to biofuel and more valuable chemicals.