Synthesis of metal oxide-hierarchical ZSM-5 (CO₃O₄/ZSM-5 and Fe₂O₃/ZSM-5) as catalysts for partial oxidation of biomethane to methanol

This study presents a partial oxidation of biomethane from anaerobic organic waste of cow dung (83.7 % of methane and 16.3 % of oxygen) to methanol using modified cobalt and iron metal oxide-hierarchical ZSM-5 catalysts. Hierarchical ZSM-5 was synthesized using double template methods with tetrapropylammonium hydroxide (TPAOH) and dimethyl diallyl ammonium chloride acrylamide copolymer (PDDAM) as the first and secondary templates, respectively. The as-synthesized ZSM-5 materials were characterized with Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Fourier Transform Infrared (FTIR), X-Ray Diffraction (XRD), and the results show the similarities of physicochemical properties with standard ZSM-5 materials. The hierarchical ZSM-5 was then modified with cobalt or iron oxides through impregnation with incipient wetness. The results of XPS analysis show that the impregnated cobalt and iron metal oxide are Co₃O₄ and Fe₂O₃, respectively. While the AAS analysis indicates that the metal content in Co₃O₄/ZSM-5 and Fe₂O₃/ZSM-5 are 2.1 % (Co) and 2.4 % (Fe), respectively. The partial oxidation of bio-methane to methanol was carried out in an atmospheric fixed batch reactor, c.a. 200 mL, with biomethane to N₂ ratio of 0,2:2 (in bar). The results of application using biomethane show the hierarchical Fe₂O₃/ZSM-5 catalyst has higher methanol yield (17.61 %), compared to the yield by using hierarchical Co₃O₄/ZSM-5 (10.99 %). In addition, no side product is detected after reaction. Thus, it can be concluded that Fe₂O₃ is more active than Co₃O₄ as catalyst and biomethane can be utilized as source in this partial oxidation reaction.