Switchable single-atom catalysts for highly selective C-C coupling in direct methane oxidation.

Direct selective conversion of methane into high value-added chemical products has long attracted attention in both industry and academia. The production of C2 oxygenates is especially challenging owing to the requirement for both C-H activation and C-C coupling. Here we report a boron nanosheet-supported Cu single atom with Cu-B4 sites (Cu-SAs/B), which can effectively catalyse the conversion of methane to acetic acid with 97% selectivity and a high activity of 221.3 mmol gCu-1 h-1 without the addition of CO. In situ X-ray absorption fine structure analysis reveals that Cu single atoms undergo reversible 'switching' to Cu4 clusters under CH4 oxidation conditions, enabling efficient C-H activation and C-C coupling. The switching behaviour is triggered by the presence of H2O2, and the coupling occurs between CH3* and CHO* intermediates formed on Cu single atoms and Cu clusters, respectively, as confirmed by in situ spectroscopic techniques. These findings provide a proof of concept for designing highly effective methane oxidation catalysts based on switchable nanocatalysts.