CH3 radical-mediated direct methane to methanol conversion over CuO supported on rutile oxides

[Display omitted] •The oxygen site of supported CuO exhibits a characteristic of a radical anion.•The radical anionic oxygen enables homolytic C-H cleavage, resulting in a •CH3.•The CH3 radical captured by the Cu site enables the CH3-OH coupling to form CH3OH.•SnO2 offers a balanced reactivity for C-H activation and C-O formation. Direct conversion of methane into methanol is an attractive strategy for the production of manifold value-added chemicals. Herein, we investigated the conversion of methane to methanol over CuO supported on the rutile metal oxides (TiO2, SnO2 and RuO2) based on results of density functional theory (DFT) calculations. The results show that the oxygen site of the supported CuO exhibits the characteristics of a radical anion. This radical anionic oxygen site enables homolytic C-H cleavage by abstracting the hydrogen atom, resulting in a CH3 radical. The CH3 radical captured by the Cu site next to the radical anionic oxygen enables the coupling of CH3 and OH to form a C-O bond, resulting in methanol. The free energy of activation for C-H activation and C-O formation were found to correlate linearly with the p band center of the radical anionic oxygen, but the slope has the opposite signs, i.e., a lower free energy of activation for C-H scission corresponds to a higher free energy formation for C-O formation. Among rutile oxides studied, SnO2 offers a balanced reactivity for C-H activation and C-O formation. These findings demonstrate the presence of the radical anionic oxygen on rutile oxide-supported CuO catalyst and their crucial role in regulating the reactivity for direct methane to methanol conversion. The mechanistic insights from this study will benefit the development of supported copper oxide catalysts for effective methane conversion.