Steering the reaction pathway of methane-to-oxygenates with zero CO2 production via photo–thermal catalysis

Abstract

The direct conversion of CH4 into liquid oxygenates via heterogeneous catalysis is highly challenging due to the facile overoxidation of target products. Herein, we present a potential Ag-modified In2O3 photo–thermal catalyst that enables the selective oxidation of CH4 to CH3OH and HCHO using molecular O2 under mild conditions (150°C, Xe lamp irradiation). The optimized Ag-3/In2O3 catalyst exhibits remarkable performance, achieving 100% selectivity toward liquid oxygenates with complete suppression of CO2 formation, and delivers a high production rate of 6544 μmol·g−1·h−1, 2.6 times greater than that under pure photocatalysis at 25°C. Mechanistic studies reveal that photogenerated holes facilitate C–H bond activation to form ·CH3 radicals, while O2 is selectively reduced at electron-rich Ag sites to generate ·OH species. Meanwhile, it demonstrates that excessive ·OH generation on the Ag-10/In2O3 contrast catalyst promotes HCHO overoxidation to CO2, highlighting the importance of ·OH regulation in determining product selectivity over the Ag-3/In2O3 catalyst. Moreover, combined with the experiments and DFT calculations, demonstrates that In2O3 with a suitable band structure exhibits weak adsorption affinity toward CH3OH and HCHO, while also supplying an in-depth understanding of the zero CO2 emissions in this catalysis process. The work illustrates that the strategic coupling of thermal and photocatalytic pathways enhances charge-carrier utilization and promotes selective radical chemistry for efficient CH4 valorization.