Mild-condition methane conversion with oxygen by an ultrasound-catalysis coupling process

Mild-condition methane (CH4) oxidation into valuable chemicals using earth-abundant oxygen (O2) is a highly desirable yet challenging process due to the chemical inertness of CH4 and the low reactivity of O2. Herein, we report an ultrasound-catalysis coupling strategy for highly efficient conversion of CH4 into high-value oxygenates under mild conditions, using O2 as an oxidant and carbon nanotube-supported platinum nanoparticles (Pt/CNT) as a catalyst. It achieves a superior formation rate of 3727 μmol gcat.−1 h−1 and a selectivity of 92% for C1-2 oxygenates at 5 oC and 0.1 MPa, significantly surpassing both previously reported thermo-catalytic and ultrasound-driven processes under low-temperature conditions. We find that ultrasound-driven surface cleaning effect enhances the exposure of active Pt sites, thereby facilitating the adsorption of CH4 and O2. Furthermore, the localized and instantaneous high-temperature and high-pressure microenvironment generated by ultrasonic cavitation not only promotes the activation of CH4 and O2 for C−H cleavage and C−O coupling, but also accelerates the mass transfer of reactants and products. The oxidation of methane (CH4) into value-added chemicals under mild conditions using earth-abundant oxygen (O2) is highly desirable but remains challenging due to the chemical inertness of CH4 and the low reactivity of O2. Here, the authors present an ultrasound-catalysis coupled strategy that enables highly efficient conversion of CH4 into high-value oxygenates under mild conditions.