Cu single atoms on defective carbon nitride for photocatalytic oxidation of methane to methanol with selectivity over 92%

doi:10.1016/S1872-2067(25)64730-9

Abstract

Abstract:

The photocatalytic oxidation of methane to methanol using molecule oxygen directly is an attractive catalytic reaction, but designing catalysts to avoid over-oxidation remains a significant challenge. Herein, Cu single-atom anchored on the defective carbon nitride structure (Cu SA/Def-CN) is designed for selective photocatalytic oxidation of methane into methanol using O₂ under mild conditions. The Cu SA/Def-CN catalyst exhibits a high methanol selectivity of 92.8% under optimized conditions. Mechanistic studies reveal a synergistic effect between Def-CN and Cu SA, where Def-CN is responsible for the in-situ generation of hydrogen peroxide, which is subsequently decomposed by the Cu SA sites to produce ·OH radicals that play a key role in the rate-determining step of methane activation to form methanol. Additionally, the presence of Cu SA not only enhances the electron-hole separation efficiency and improves the transfer of the photo-generated charges, but also increases the number of active sites for methane adsorption and activation. These insights provide valuable guidance for designing efficient catalysts for the highly selective photocatalytic oxidation of methane to methanol.

Key words: Methane, Photocatalysis, Cu single atoms, Defective carbon nitride, Hydrogen peroxide

Bo Feng, Danning Feng, Yan Pei, Baoning Zong, Minghua Qiao, Wei Li. Cu single atoms on defective carbon nitride for photocatalytic oxidation of methane to methanol with selectivity over 92%[J]. Chinese Journal of Catalysis, 2025, 76: 96-107.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(25)64730-9

https://www.cjcatal.com/EN/Y2025/V76/I9/96

Figures/Tables 5

Fig. 1. XRD patterns (a) and EPR spectra (b) of Def-CN and Cu SA/Def-CN. SEM (c) and TEM (d) images of Cu SA/Def-CN. (e) Aberration-corrected HAADF-STEM images of Cu SA/Def-CN. (f) EDS mapping of Cu SA/Def-CN.

Fig. 2. C K-edge (a) and N K-edge (b) XANES of Def-CN and Cu SA/Def-CN. Normalized XANES (c) and EXAFS (d) results of Cu SA/Def-CN at the Cu K-edge. (e) WT-EXAFS of the Cu SA/Def-CN, Cu foil and CuO samples.

Fig. 3. Photocatalytic oxidation of CH4 with O2 over Cu SA/Def-CN. (a) Time-dependent product distribution over Cu SA/Def-CN. (b) Different loading of Cu on Def-CN. (c) Effect of the volume of distilled water on the product distribution over Cu SA/Def-CN. (d) Dependence of methane oxidation over Cu SA/Def-CN at different total pressure. (e) Comparison of the productivity and selectivity to CH3OH over Cu SA/Def-CN with literature. Reaction conditions: 10 mg of catalyst, 20 mL of water, 20 bar of CH4, 1 bar of O2, 25 °C, 300 < λ < 780 nm, light intensity of 200 mW cm?2, stirring rate of 800 rpm. For reaction condition studies, only the specified parameter is changed.

Fig. 4. The UV-vis diffuse reflectance spectra (a), corresponding Tauc plots (b), steady-state PL spectra (c), time-resolved PL decay spectra (d), photocurrent response curves (e), and EIS Nyquist plots (f) of Def-CN and Cu SA/Def-CN catalysts.

Fig. 5. In-situ EPR spectra of and Cu SA/Def-CN. (a) Dissolving O2 in CH3OH under different light conditions. (b) Dissolving O2 in water aqueous solution under different light conditions. DMPO is used as the radical trapping agent. (c) The fluorescent spectra of 2-hydroxyterephthalic acid for ?OH radical detection in O2 atmosphere in the presence of Def-CN and Cu SA/Def-CN or in the absence of catalyst. (d) CH4-TPD profiles of Def-CN and Cu SA/Def-CN. (e) The proposed catalytic mechanism for the oxidation of CH4 to CH3OH.

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