Enabling Specific Photocatalytic Methane Oxidation by Controlling Free Radical Type

Selective CH4 oxidation to CH3OH or HCHO with O-2 in H2O under mild conditions provides a desired sustainable pathway for synthesis of commodity chemicals. However, manipulating reaction selectivity while maintaining high productivity remains a huge challenge due to the difficulty in the kinetic control of the formation of a desired oxygenate against its overoxidation. Here, we propose a highly efficient strategy, based on the precise control of the type of as-formed radicals by rational design on photocatalysts, to achieve both high selectivity and high productivity of CH3OH and HCHO in CH4 photooxidation for the first time. Through tuning the band structure and the size of active sites (i.e., single atoms or nanoparticles) in our Au/In2O3 catalyst, we show alternative formation of two important radicals, center dot OOH and center dot OH, which leads to distinctly different reaction paths to the formation of CH3OH and HCHO, respectively. This approach gives rise to a remarkable HCHO selectivity and yield of 97.62% and 6.09 mmol g(-1) on In2O3-supported Au single atoms (Au-1/In2O3) and an exceptional CH3OH selectivity and yield of 89.42% and 5.95 mmol g(-1) on In2O3-supported Au nanoparticles (AuNPs/In2O3), respectively, upon photocatalytic CH4 oxidation for 3 h at room temperature. This work opens a new avenue toward efficient and selective CH4 oxidation by delicate design of composite photocatalysts.

Automated summary

We have achieved high selectivity and high productivity of CH3OH and HCHO in CH4 photooxidation for the first time by precisely controlling the type of as-formed radicals through rational design on photocatalysts. By tuning the band structure and active sites (single atoms or nanoparticles) on Au/In2O3 catalysts, we can generate two different radicals, center dot OOH and center dot OH, leading to the formation of CH3OH and HCHO, respectively. The results show remarkable selectivity and yield of HCHO (97.62% and 6.09 mmol g(-1)) on In2O3-supported Au single atoms (Au-1/In2O3) and exceptional selectivity and yield of CH3OH (89.42% and 5.95 mmol g(-1)) on In2O3-supported Au nanoparticles (AuNPs/In2O3) during photocatalytic CH4 oxidation at room temperature for 3 hours. This work opens up a new avenue for efficient and selective CH4 oxidation through the design of composite photocatalysts.