Catalyst-free partial oxidation of methane under ambient conditions boosted by mechanical stirring-enhanced ultrasonic cavitation.

The partial oxidation of methane (POM) into value-added C chemicals (e.g., CHOH, HCHO, and CO) offers a promising approach for natural gas utilization under mild conditions. However, existing POM systems often rely on complex catalyst designs and the addition of extra oxidants. Here, we developed a catalyst-free POM system by integrating mechanical stirring with a low-frequency ultrasonic field. A high production rate of C chemicals (129.26 µmol h) and methane conversion rate (22%) were achieved under ambient conditions (298 K, P = 0.1 bar, P = 0.1 bar, P = 0.8 bar). Mechanism studies revealed that the introduction of mechanical stirring amplified the ultrasonic cavitation effect, promoting the in-situ release of reactive oxygen species. Reaction pathway investigation confirmed that hydroxyl radicals facilitated the cleavage of methane C-H bonds and that oxygen participated in the generation of POM products. This strategy provides a sustainable avenue for the value-added conversion of methane.