Bisulfate-mediated selective methane oxidation under mild aqueous conditions.

The selective oxidation of methane under mild conditions remains a formidable challenge because of the inert C─H bond and the ease of over-oxidation. Here we report a facile strategy that enables methane conversion at room temperature and ambient pressure using molecular O2 and commercially available Cu powder in dilute aqueous H2SO4. The reaction is capable of proceeding with only trace CO2 formation, producing methyl bisulfate and methanol as the primary partial oxidation products. In situ Raman spectroscopy indicates that an in situ O2-derived Cu2O surface is the reaction-relevant phase associated with C─H bond activation. The observed selectivity arises from bisulfate adsorption on this Cu2O surface, which suppresses methanol over-oxidation, together with the interception of surface-generated methyl intermediates to form oxidation-resistant methyl bisulfate. This Cu/O2-H2SO4 system demonstrates that methane can be selectively oxidized under mild aqueous conditions and provides mechanistic insight into Cu/O2-mediated oxidation, suggesting a bisulfate-assisted approach to suppressing over-oxidation that may be applicable to other substrates.