Tandem photo-oxidation of methane to methanol at room temperature and pressure over Pt/TiO2

In the process of methane (CH4) oxidation to methanol (CH3OH), CH3OH is more easily oxidized than CH4, resulting in inevitable peroxide phenomenon. In this work, we innovatively proposed a tandem reaction pathway to obtain a photocatalytic oxidation process of CH4 with high activity and selectivity. This work confirms that the methyl hydrogen peroxide (CH3OOH), the first product of CH4 oxidation by H2O2, is then completely reduced to CH3OH in an electron-rich environment. Under irradiation, H2O2 was excited into hydroxyl radicals (·OH) and hydroperoxyl radicals (·OOH) on brookite TiO2 photocatalyst. The ·OH oxidized CH4 to form methyl radicals (·CH3), which then reacted with ·OOH to form CH3OOH. CH3OOH gained electrons on Pt nanoparticles (NPs) and was reduced to CH3OH. At this point, low concentration of ·OH was difficult to further oxidize CH3OH, so that it can exist stably. Under the conditions of room temperature (25 °C) and atmospheric pressure, the productivity of CH3OH was 883 µmol/(g·h), which was 4 times more than the reported photocatalytic CH4 oxidation system with the same reaction conditions, and the selectivity was 100% in liquid products (98.77% for all products). The photocatalyst showed excellent stability and maintained > 85% product activity after 9 catalytic cycles. This work contributed to the development of highly efficient and selective CH4 photooxidation system under mild conditions. [graphic not available: see fulltext]