Single-atom catalysts (SACs) have attracted wide interest from researchers, as they promisingly bridge the gap between homogeneous and heterogeneous catalysts.

Direct functionalization of methane remains a key challenge, especially for using non-noble metal catalysts. We demonstrated that TiO 2 nanorods with abundant oxygen vacancies enabled mild oxidation of methane by H 2 O 2 into formaldehyde (HCHO) without light irradiation. The activity of TiO 2 nanorods with the concentration gradient of oxygen vacancies (V O ) increased with the V O concentration. In H 2 O 2 aqueous solution under 30 bar of CH 4 at 70 °C for 1 h, the TiO 2 nanorods with the most abundant V O exhibited a total oxygenate yield of 40.80 μmol, among which the selectivity for HCHO was 64.1%. On the basis of the catalytic and spectroscopic data, we identified the reaction intermediates and accordingly mapped the reaction scheme. Specifically, H 2 O 2 is activated on Ti atoms near V O to form surface peroxo intermediates, followed by the activation of CH 4 to produce methoxy groups. The methoxy group can react either with water to form methanol or with hydroxyl radicals to form CH 3 OOH. Methanol is attacked by hydroxyl radicals and dehydrated to form •CH 2 OH that further reacts with hydroxyl radicals and is dehydrated to HCHO. CH 3 OOH directly undergoes dehydration to engender HCHO.

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