Controlling N-doping type in carbon to boost single-atom site Cu catalyzed transfer hydrogenation of quinoline
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Controlling N-doping type in carbon to boost single-atom site Cu catalyzed transfer hydrogenation of quinoline Jian Zhang1,§, Caiyan Zheng2,§, Maolin Zhang3, Yajun Qiu1, Qi Xu1, Weng-Chon Cheong4, Wenxing Chen5, Lirong Zheng6, Lin Gu7, Zhengpeng Hu2, Dingsheng Wang1 (), and Yadong Li1 () 1
Department of Chemistry, Tsinghua University, Beijing 100084, China School of Physics, Nankai University, Tianjin 300071, China 3 KAUST Catalysis Center (KCC), King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia 4 Department of Physics and Chemistry, Faculty of Science and Technology, University of Macau, Taipa, Macau SAR, China 5 School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, China 6 Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China 7 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China § Jian Zhang and Caiyan Zheng contributed equally to this work. 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 3 July 2020 / Revised: 6 July 2020 / Accepted: 8 July 2020
ABSTRACT Single-atom site (SA) catalysts on N-doped carbon (CN) materials exhibit prominent performance for their active sites being M-Nx. Due to the commonly random doping behaviors of N species in these CN, it is a tough issue to finely regulate their doping types and clarify their effect on the catalytic property of such catalysts. Herein, we report that the N-doping type in CN can be dominated as pyrrolic-N and pyridinic-N respectively through compounding with different metal oxides. It is found that the proportion of distinct doped N species in CN depends on the acidity and basicity of compounded metal oxide host. Owing to the coordination by pyrrolic-N, the SA Cu catalyst displays an enhanced activity (two-fold) for transfer hydrogenation of quinoline to access the valuable molecule tetrahydroquinoline with a good selectivity (99%) under mild conditions. The higher electron density of SA Cu species induced by the predominate pyrrolic-N coordination benefits the hydrogen transfer process and reduces the energy barrier of the hydrogenation pathway, which accounts for the improved catalytic effeciency.
KEYWORDS nitrogen-doping type, metal oxide, nitrogen-doped carbon, single-atom site catalyst, transfer hydrogenation
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Introduction
Nitrogen-doped carbon (CN) material supported single-atom site (SA) catalysts have attracted growing interest for their broad applications in electrochemistry [1–3], organic synthesis [4–6] and industrial catalysis [7–9]. In general, metal centers (M) in such catalysts are coordinated with nitrogen atoms (N) embedded in the matrix of carbon, forming M-Nx as active sites [10–13]. The nature of these nitrogen atoms thereby have great effect on the catalytic property of the metal centers in M-Nx [14]. As for most CN carriers in SA catalysts, nitrogen atoms are
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