The Importance of Si─ONa─Al Moieties in Fe/ZSM-5 Zeolite Catalysts for Selective Oxidation of Methane to Acetic Acid

Selective oxidation of methane to acetic acid with high activity and selectivity remains a significant challenge. Brønsted acid sites (Si─OH─Al) are well-known for their crucial role in facilitating methane oxidation to acetic acid over zeolite-based catalysts. Here, we reported that Fe/ZSM-5-0.25Na with abundant Si─ONa─Al moieties outperformed Fe/ZSM-5 (rich in Brønsted acid sites) in methane oxidation to acetic acid using H₂O₂ in the presence of CO. The Fe/ZSM-5-0.25Na yielded 144.1 µmol of oxygenated products, achieving an acetic acid selectivity of 81.8% at 50 °C for 2.0 h. These results surpass the performance of the Fe/ZSM-5 catalyst, which produced 131.4 µmol of oxygenated products with an acetic acid selectivity of 58.4%. Spectroscopic characterizations and mechanistic studies revealed that the Si─ONa─Al moieties in Fe/ZSM-5-0.25Na facilitated electron donation to iron species, forming electron-rich iron sites. These electron-rich iron species promoted CO insertion and enhanced the formation of acetic acid through carbon–carbon coupling of methane and CO.