Methane C(sp³)–H bond activation by water microbubbles

Abstract

Microbubble-induced oxidation offers an effective approach for activating the C(sp³)-H bond of methane under mild conditions, achieving a methane activation rate of up to 6.7% per hour under optimized parameters. In this study, microbubbles provided an extensive gas-liquid interface that promoted the formation of hydroxyl (OH˙) and hydrogen radicals (H˙), which facilitated the activation of methane, leading to the generation of methyl radicals (CH₃˙). These species further participated in free-radical reactions at the interface, resulting in the production of ethane and formic acid. The microbubble system was optimized by adjusting gas-liquid interaction time, water temperature, and bubble size, with the optimal conditions (150 s of water-gas interaction, 15 °C, 50 μm bubble size) yielding a methane conversion rate of 171.5 ppm h^-1, an ethane production rate of 23.5 ppm h^-1, and a formic acid production rate of 2.3 nM h^-1 during 8 h of continuous operation. The stability and efficiency of this process, confirmed through electron spin resonance, high-resolution mass spectrometry, and gas chromatography, suggest that microbubble-based methane activation offers a scalable and energy-efficient pathway for methane utilization.