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

Abstract

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 g_cat.^-1 h^-1 and a selectivity of 92% for C_1-2 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.