中国科学技术大学潘洋团队报道了用原位同步辐射光电离质谱法揭示甲烷在Ag-ZnO上光催化氧化中甲基自由基的命运。相关研究成果发表在2023年5月23日出版的《德国应用化学》。

光催化已成为在温和条件下直接活化和转化甲烷的理想方法。在该反应中，甲基自由基（CH3）被认为是影响产物产率和选择性的关键中间体。然而，直接观察CH3和其他中间体仍然具有挑战性。

该文中，研究人员开发了一个矩形光催化反应器，结合原位同步辐射光电离质谱（SR-PIMS），在Ag-ZnO上光催化甲烷氧化过程中，在几百微秒内检测反应中间体。直接观察到光生空穴（O^-）产生的气相CH3，并证明其形成被共吸附的氧分子显著增强。甲氧基（CH3O）和甲醛（HCHO）被证实是甲烷光催化过氧化为CO₂的关键C1中间体。CH3的气相自耦反应有助于乙烷的形成，这表明CH3解吸在乙烷的高选择性合成中起着关键作用。基于观察到的中间体，可以清楚地说明甲烷光催化氧化的CH3引发的反应网络，这有助于研究甲烷光催化转化过程。

附：英文原文

Title: Illustrating the Fate of Methyl Radical in Photocatalytic Methane Oxidation over Ag-ZnO by in situ Synchrotron Radiation Photoionization Mass Spectrometry

Author: Chengyuan Liu, Bing Qian, Tianci Xiao, Chunchun Lv, Jinsong Luo, Jun Bao, Yang Pan

Issue&Volume: 2023-05-23

Abstract: Photocatalysis has emerged as an ideal method for the direct activation and conversion of methane under mild conditions. In this reaction, methyl radical (CH3) was deemed a key intermediate that affected the yields and selectivity of the products. However, direct observation of CH3 and other intermediates is still challenging. Here, a rectangular photocatalytic reactor coupled with in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) was developed to detect reactive intermediates within several hundred microseconds during photocatalytic methane oxidation over Ag-ZnO. Gas phase CH3 generated by photogenerated holes (O-) was directly observed, and its formation was demonstrated to be significantly enhanced by coadsorbed oxygen molecules. Methoxy radical (CH3O) and formaldehyde (HCHO) were confirmed to be key C1 intermediates in photocatalytic methane overoxidation to CO2. The gas-phase self-coupling reaction of CH3 contributes to the formation of ethane, which indicates the key role of CH3 desorption in the highly selective synthesis of ethane. Based on the observed intermediates, the reaction network initiated from CH3 of photocatalytic methane oxidation could be clearly illustrated, which is helpful for studying the photocatalytic methane conversion processes.

DOI: 10.1002/anie.202304352

Source: https://onlinelibrary.wiley.com/doi/10.1002/anie.202304352