Highly Selective Synthesis of Acetic Acid from Hydroxyl-Mediated Oxidation of Methane at Low Temperatures

Direct methane conversion and, in particular, the aerobic oxidation to acetic acid, remain an eminent challenge. Here, we reported a zeolite-supported Au-Fe catalyst (Au-Fe/ZSM-5) that converted methane to acetic acid with molecular oxygen as an oxidant in the presence of CO. Specifically, Au nanoparticles catalyzed the formation of hydroxyl species from the reaction of CO, O₂, and H₂O, meanwhile ZSM-5-supported atomically dispersed Fe species were responsible for the hydroxyl-mediated coupling of CH₄ and CO to generate acetic acid. The reaction over 50 mg of Au-Fe/ZSM-5 under 62 bar (CH₄ : CO : O₂=14 : 14 : 3) at 120 °C for 3.0 h yielded 5.7 millimoles of acetic acid per gram of the catalyst (mmol g_cat ^-1) with the selectivity of 92 %, outperformed most of reported catalysts. Significantly, the catalyst remained active even at 60 °C. We anticipate that this hydroxyl-mediated route may guide the design of optimized catalysts for the direct methane functionalization at low temperatures.