Zheng Kai, Wu Mingyu, Zhu Juncheng, Zhang Wei, Liu Siying, Zhang Xiaojing, Wu Yang, Li Li, Li Bangwang, Liu Wenxiu, Hu Jun, Liu Chengyuan, Zhu Junfa, Pan Yang, Zhou Meng, Sun Yongfu, Xie Yi
Hefei National Research Center for Physical Sciences at Microscale, University of Science and Technology of China, Hefei 230026, China.
Instruments Center for Physical Science, University of Science and Technology of China, Hefei 230026, China.
J Am Chem Soc. 2024 May 1;146(17):12233-12242. doi: 10.1021/jacs.4c03546. Epub 2024 Apr 16.
Photocatalytic conversion of methane (CH) to ethane (CH) has attracted extensive attention from academia and industry. Typically, the traditional oxidative coupling of CH (OCM) reaches a high CH productivity, yet the inevitable overoxidation limits the target product selectivity. Although the traditional nonoxidative coupling of CH (NOCM) can improve the product selectivity, it still encounters unsatisfied activity, arising from being thermodynamically unfavorable. To break the activity-selectivity trade-off, we propose a conceptually new mechanism of HO-triggered CH coupling, where the HO-derived ·OH radicals are rapidly consumed for activating CH into ·CH radicals exothermically, which bypasses the endothermic steps of the direct CH activation by photoholes and the interaction between ·CH and ·OH radicals, affirmed by characterization techniques, femtosecond transient absorption spectroscopy, and density-functional theory calculation. By this pathway, the designed Au-WO nanosheets achieve unprecedented CH productivity of 76.3 mol mol h with 95.2% selectivity, and TON of 1542.7 (TOF = 77.1 h) in a self-designed flow reactor, outperforming previously reported photocatalysts regardless of OCM and NOCM pathways. Also, under outdoor natural sunlight irradiation, the Au-WO nanosheets exhibit similar activity and selectivity toward CH production, showing the possibility for practical applications. Interestingly, this strategy can be applied to other various photocatalysts (Au-WO, Au-TiO, Au-CeO, Pd-WO, and Ag-WO), showing a certain universality. It is expected that the proposed mechanism adds another layer to our understanding of CH-to-CH conversion.
甲烷（CH₄）光催化转化为乙烷（C₂H₆）已引起学术界和工业界的广泛关注。通常，传统的甲烷氧化偶联（OCM）能实现较高的CH₄生产率，但不可避免的过度氧化限制了目标产物的选择性。尽管传统的甲烷非氧化偶联（NOCM）可以提高产物选择性，但由于热力学不利，其活性仍不尽人意。为了打破活性与选择性之间的权衡，我们提出了一种全新的由HO引发的CH₄偶联机制，其中HO衍生的·OH自由基被快速消耗，以放热方式将CH₄活化为·CH₃自由基，这绕过了光生空穴直接活化CH₄的吸热步骤以及·CH₃与·OH自由基之间的相互作用，飞秒瞬态吸收光谱和密度泛函理论计算等表征技术证实了这一点。通过这条途径，所设计的Au-WO₃纳米片在自行设计的流动反应器中实现了前所未有的76.3 μmol g⁻¹ h⁻¹的CH₄生产率，选择性为95.2%，TON为1542.7（TOF = 77.1 h⁻¹），优于此前报道的光催化剂，无论OCM还是NOCM途径。此外，在户外自然阳光照射下，Au-WO₃纳米片对C₂H₆生成表现出相似的活性和选择性，显示出实际应用的可能性。有趣的是，该策略可应用于其他各种光催化剂（Au-WO₂、Au-TiO₂、Au-CeO₂、Pd-WO₃和Ag-WO₃），具有一定的通用性。预计所提出的机制将加深我们对CH₄到C₂H₆转化的理解。
