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.