Highly selective photocatalytic oxidation of methane to methyl hydroperoxide

Partial oxidation of methane into primary oxidation products with high value remains a challenge. In this work, photocatalytic oxidation of methane (CH4) with high methyl hydroperoxide (CH3OOH) selectivity is achieved using pure titanium oxide (TiO2) without any cocatalyst at room temperature and atmospheric pressure. The CH3OOH production rate can reach up to 2050 ± 88 µmol·g−1·h−1 at pH ≈ 7.0 with 100% selectivity in the liquid product. The stable reaction cycle can reach more than 30 times. This low-cost system achieves superior CH4 conversion activity and selectivity compared with similar work. The energy of hydrogen peroxide (H2O2) to adsorbed hydroperoxyl radical (⋆OOH) has a significantly lower reaction energy than conversion to adsorbed hydroxyl radical (⋆OH) on the (210) surface of the TiO2. The ⋆OOH preferentially combines with methyl radical (·CH3) to form the most energetically favorable CH3OOH. The mild oxidative environment of this system prevents the reduction of CH3OOH to CH3OH or over-oxidation of CH4, which ensures the final CH3OOH with high selectivity and stability. This work provided a low-cost but highly efficient method to achieve partial oxidation with superior selectivity, i.e., to convert CH4 into high-value chemicals.