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.