Jiang Wenbin, Low Jingxiang, Mao Keke, Duan Delong, Chen Shuangming, Liu Wei, Pao Chih-Wen, Ma Jun, Sang Shuaikang, Shu Chang, Zhan Xiaoyi, Qi Zeming, Zhang Hui, Liu Zhi, Wu Xiaojun, Long Ran, Song Li, Xiong Yujie
Hefei National Laboratory for Physical Sciences at the Microscale, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), School of Chemistry and Materials Science, and National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China.
Institute of Energy, Hefei Comprehensive National Science Center, 350 Shushanhu Road, Hefei, Anhui 230031, China.
J Am Chem Soc. 2021 Jan 13;143(1):269-278. doi: 10.1021/jacs.0c10369. Epub 2020 Dec 29.
Photocatalysis provides an intriguing approach for the conversion of methane to multicarbon (C) compounds under mild conditions; however, with methyl radicals as the sole reaction intermediate, the current C products are dominated by ethane, with a negligible selectivity toward ethylene, which, as a key chemical feedstock, possesses higher added value than ethane. Herein, we report a direct photocatalytic methane-to-ethylene conversion pathway involving the formation and dehydrogenation of alkoxy (i.e., methoxy and ethoxy) intermediates over a Pd-modified ZnO-Au hybrid catalyst. On the basis of various characterizations, it is revealed that the Pd-induced dehydrogenation capability of the catalyst holds the key to turning on the pathway. During the reaction, methane molecules are first dissociated into methoxy on the surface of ZnO under the assistance of Pd. Then these methoxy intermediates are further dehydrogenated and coupled with methyl radical into ethoxy, which can be subsequently converted into ethylene through dehydrogenation. As a result, the optimized ZnO-AuPd hybrid with atomically dispersed Pd sites in the Au lattice achieves a methane conversion of 536.0 μmol g with a C compound selectivity of 96.0% (39.7% CH and 54.9% CH in total produced C compounds) after 8 h of light irradiation. This work provides fresh insight into the methane conversion pathway under mild conditions and highlights the significance of dehydrogenation for enhanced photocatalytic activity and unsaturated hydrocarbon product selectivity.
光催化为在温和条件下将甲烷转化为多碳（C）化合物提供了一种引人入胜的方法；然而，由于甲基自由基是唯一的反应中间体，目前的C产物以乙烷为主，对乙烯的选择性可忽略不计，而乙烯作为一种关键的化学原料，其附加值高于乙烷。在此，我们报道了一种直接的光催化甲烷制乙烯转化途径，该途径涉及在钯改性的ZnO-Au混合催化剂上形成和脱氢烷氧基（即甲氧基和乙氧基）中间体。基于各种表征，揭示了催化剂的钯诱导脱氢能力是开启该途径的关键。在反应过程中，甲烷分子首先在钯的协助下在ZnO表面解离为甲氧基。然后这些甲氧基中间体进一步脱氢并与甲基自由基偶联形成乙氧基，随后乙氧基可通过脱氢转化为乙烯。结果，在光照8小时后，在金晶格中具有原子分散钯位点的优化ZnO-AuPd混合催化剂实现了536.0 μmol g的甲烷转化率，C化合物选择性为96.0%（在总生成的C化合物中，乙烯占39.7%，乙烷占54.9%）。这项工作为温和条件下的甲烷转化途径提供了新的见解，并突出了脱氢对于提高光催化活性和不饱和烃产物选择性的重要性。
