Direct conversion of CH4 to oxygenates is regarded as a “holy grail” in the chemistry community. Herein, a specially designed metal-free rTiO2/GO catalyst was reported for photocatalytic oxidation of CH4. It was found that the presence of graphene oxide (GO) retarded the recombination of photo-generated electrons and holes (h+), whereas defective oxygen vacancies can be introduced upon reduction of TiO2 (rTiO2). The C–H bond of the CH4 molecule can be readily activated with a considerably low energy barrier of 1.67 eV, and the generated CH3OOH* intermediate can be stabilized by the oxygen vacancies. As such, CH4 can be directly oxidized to liquid oxygenates with extraordinary efficiency (7.65 mmol g−1 h−1 yield and 90% selectivity). More interestingly, HCHO was found to be the major product rather than CH3OH; such an extension was rarely reported, it provides not only a more valuable route for CH4 upgrading, but also a new basis of natural gas-based chemistry upon tandem conversion of HCHO.
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