【Frontiers in HaiChuan Technology】Dalian Institute of Chemical Physics develops sub-nanoscale hydrides to achieve a new path for the non-oxidative coupling of benzene

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Recently, a team led by researchers Chen Ping and Guo Jianping from our Institute’s Hydrogenide Energy Chemistry Research Center (Group DNL1901), in collaboration with Associate Professor Rao Li from Central China Normal University, developed a sub-nanometer structured catalyst loaded with europium hydride. This catalyst enabled the catalytic conversion of benzene into biphenyl through direct dehydrogenation coupling under mild, non-oxidizing conditions. This study reveals the unique mechanism by which hydrides facilitate the activation of inert carbon-hydrogen (C-H) bonds, providing a new approach for the green and efficient formation of carbon-carbon (C-C) bonds. Biphenyl compounds are important structural units in the fields of organic synthesis and fine chemicals. Constructing C-C bonds through the direct activation of C-H/C-H bonds is considered an ideal synthetic route that is economical and environmentally friendly. However, the C-H bond energy of benzene molecules is as high as 113 kcal·mol-1, resulting in high chemical inertness and difficulty in activation ； On the other hand, from a thermodynamic perspective, the process of direct coupling of benzene to form biphenyl along with hydrogen is also an unfavorable reaction. Currently, the C-C bond coupling of benzene typically relies on oxidation coupling reactions catalyzed by precious metals (such as palladium), and such reactions often require the use of excess oxidants and complex additives. Moreover, the few existing non-oxidative coupling systems mostly require stoichiometric amounts of strong reducing agents (such as alkali metals, potassium graphite, etc.), and a subsequent hydrolysis step is needed to release the biphenyl product, making it difficult to achieve a catalytic cycle. Therefore, achieving the catalytic coupling of benzene molecules under non-oxidizing conditions is considered a highly challenging research topic. The research team led by Chen Ping and Guo Jianping focuses on the activation and transformation of inert small molecules mediated by hydride materials. In the preliminary work, the team systematically explored hydride materials for nitrogen activation conversion (Nat. Chem., 2017 ； Nat. Energy, 2018 ； Nat. Catal., 2021 ； Nat. Chem., 2024), as well as reactions with organic small molecules such as acetylene and aromatic compounds (J. Am. Chem. Soc., 2021) ； J. Am. Chem. Soc., 2022 ； Nat. Commun., 2025), highlighting the unique capabilities of hydrides and demonstrating their significant potential in the activation of inert chemical bonds. Based on the aforementioned research foundation, in this work, the team employed a liquid ammonia impregnation-hydrogen reduction method to prepare highly dispersed sub-nanoscale europium hydride catalysts (EuHx/MgO). This catalyst enables the direct dehydrogenation coupling of benzene molecules without the use of oxidants or post-treatment, yielding two high-value products: biphenyl and hydrogen. Theoretical calculations indicate that the Eu-H species on the catalyst surface play a key role in C-H bond activation and C-C bond coupling: on one hand, they facilitate the activation of C-H bonds in benzene rings as well as the deprotonation process ； On the other hand, by regulating the adsorption and desorption energy barriers of benzene and biphenyl on the catalyst surface, an efficient catalytic cycle was achieved, demonstrating a new mechanism for hydride-mediated C-H activation.