Oxygen Vacancy-Rich TiO2 as an Efficient Non-noble Metal Catalyst toward Mild Oxidation of Methane Using Hydrogen Peroxide as the Oxidant

Directfunctionalization of methane remains a key challenge, especiallyfor using non-noble metal catalysts. We demonstrated that TiO2 nanorods with abundant oxygen vacancies enabled mild oxidationof methane by H2O2 into formaldehyde (HCHO)without light irradiation. The activity of TiO2 nanorodswith the concentration gradient of oxygen vacancies (V (O)) increased with the V (O) concentration.In H2O2 aqueous solution under 30 bar of CH4 at 70 degrees C for 1 h, the TiO2 nanorods withthe most abundant V (O) exhibited a totaloxygenate yield of 40.80 mu mol, among which the selectivity forHCHO was 64.1%. On the basis of the catalytic and spectroscopic data,we identified the reaction intermediates and accordingly mapped thereaction scheme. Specifically, H2O2 is activatedon Ti atoms near V (O) to form surface peroxointermediates, followed by the activation of CH4 to producemethoxy groups. The methoxy group can react either with water to formmethanol or with hydroxyl radicals to form CH3OOH. Methanolis attacked by hydroxyl radicals and dehydrated to form center dot CH2OH that further reacts with hydroxyl radicals and is dehydratedto HCHO. CH3OOH directly undergoes dehydration to engenderHCHO.