缺陷氮化碳负载铜单原子用于高选择性光催化氧化甲烷制甲醇

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

摘要/Abstract

摘要：

甲烷是强效温室气体, 通过光催化技术, 利用太阳能和半导体催化剂在常温下高选择性地将其活化转化为高附加值甲醇, 兼具重要的环境和经济意义. 然而, 传统光催化甲烷氧化催化剂常面临副产物(如甲醛和二氧化碳)生成的问题, 导致甲醇选择性较低. 因此, 设计能够实现高选择性甲醇生成的光催化剂具有重要研究价值.

本文设计并制备了一种新颖的铜单原子(Cu SA)锚定在缺陷氮化碳(Def-CN)上的光催化剂(Cu SA/Def-CN), 用于在温和条件下利用廉价的氧气高选择性地将甲烷氧化为甲醇. 首先, 筛选了多种金属修饰的Def-CN催化剂, 包括铁、钴、镍和铜. 研究发现, 在相同条件下, 由铜修饰的Def-CN催化剂表现出最佳的光催化性能. 为优化催化剂性能, 进一步考察了Cu(NO₃)₂, CuSO₄, Cu(OAc)₂和CuCl₂等铜源的影响. 研究结果表明, 以CuCl₂为铜源修饰的Def-CN催化剂具有最佳的甲醇生成活性. 在CuCl₂作为铜源的基础上, 进一步考察了铜负载量对催化性能的影响, 同时优化了包括反应时间、总压、氧分压和水量等反应条件. 在最佳条件下, Cu SA/Def-CN催化剂上经过3 h反应后, 甲醇产量达到8.9 μmol, 生成速率为297 μmol g^-1 h^-1, 选择性高达92.8%, 显著优于多数文献报道值.

为确认铜单原子的存在状态, 采用球差校正电子显微镜和X射线吸收精细结构技术, 证实了Cu SA被成功锚定在Def-CN上. 此外, 通过光电性能测量和甲烷吸附实验进一步验证了Cu SA位点不仅提高了电子-空穴的分离效率, 促进了光生电荷的转移, 并增加了甲烷的吸附和活化活性位点, 从而共同提高了光催化甲烷氧化性能. 机理研究揭示了Def-CN和Cu SA之间的协同效应. 具体而言, Def-CN结构负责原位生成H₂O₂, 过氧化氢随后在Cu SA位点的催化作用下分解生成适宜浓度的·OH自由基, 该过程有效避免了过度氧化副产物如甲醛和二氧化碳的形成, 从而显著提高了甲醇的选择性.

综上所述, 本研究提出了一种高效且高选择性的Cu SA/Def-CN光催化剂, 并揭示了其在甲烷光催化氧化反应中的优异性能, 为高性能甲烷选择性光催化氧化催化剂的设计提供了理论依据和实践指导, 也为甲烷资源的高效利用及清洁能源的开发提供了参考.

关键词: 甲烷, 光催化, 铜单原子, 缺陷氮化碳, 过氧化氢

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

封波, 冯丹宁, 裴燕, 宗保宁, 乔明华, 李伟. 缺陷氮化碳负载铜单原子用于高选择性光催化氧化甲烷制甲醇[J]. 催化学报, 2025, 76: 96-107.

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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链接本文: https://www.cjcatal.com/CN/10.1016/S1872-2067(25)64730-9

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

图/表 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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