Single cobalt sites in mesoporous N-doped carbon matrix for selective catalytic hydrogenation of nitroarenes
Single cobalt sites in mesoporous N-doped carbon matrix for selective catalytic hydrogenation of nitroarenes
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DOI：
10.1016/j.jcat.2017.10.030
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发表时间：
2018
影响因子：
7.3
通讯作者：
Xiaohui Sun;A. Olivos-Suarez;D. Osadchii;M. Romero;F. Kapteijn;J. Gascón
中科院分区：
文献类型：
--
作者：
Xiaohui Sun;A. Olivos-Suarez;D. Osadchii;M. Romero;F. Kapteijn;J. Gascón
通过水解Zn/Co咪唑骨架（BIMZIF（Co，Zn））中的原硅酸四甲酯（TMOS），然后高温热解和SiO2浸出，合成了在介孔氮掺杂碳基质中原子分散的Co-Nx（3.5wt%Co）负载型钴催化剂（Co@mesoNC）。TEM、XRD、XPS和X射线吸收光谱研究的组合证实了不存在钴纳米颗粒，并表明这些高度分散的钴物种以Co-Nx的形式存在。在碳基质中的Co-Nx位点的排他性形成归因于BIMZIF前体中大量Zn和N的存在以及该框架的孔隙空间中SiO2的存在，延长了钴原子之间的初始空间距离，从而阻碍了它们的团聚。在高温热解过程中SiO2的存在被证明对于在N掺杂的碳载体（1780 m2g-1，1.54 cm3g-1）中产生中孔性和高BET面积和孔体积是至关重要的。该非均相Co@mesoNC催化剂在温和条件下（0.5 - 3 MPa，343 - 383 K）对硝基苯选择加氢制苯胺具有较高的活性和选择性（> 99%）。当催化剂Co@mesoNC催化硝基芳烃加氢反应时，对相应的取代苯胺类化合物具有很好的选择性，介孔结构的存在改善了反应物和/或产物的传质，提高了活性Co-Nx位点的可及性，大大降低了因结垢而导致的失活。
A supported cobalt catalyst with atomically dispersed Co-Nxsites (3.5 wt% Co) in a mesoporous N-doped carbon matrix (named Co@mesoNC) is synthesized by hydrolysis of tetramethyl orthosilicate (TMOS) in a Zn/Co bimetallic zeolitic imidazolate framework (BIMZIF(Co,Zn)), followed by high-temperature pyrolysis and SiO2leaching. A combination of TEM, XRD XPS and X-ray absorption spectroscopy studies confirm the absence of cobalt nanoparticles and indicate that these highly dispersed cobalt species are present in the form of Co-Nx. The exclusive formation of Co-Nxsites in the carbon matrix is attributed to the presence of a large amount of Zn and N in the BIMZIF precursor together with the presence of SiO2in the pore space of this framework, extending the initial spatial distance between cobalt atoms and thereby impeding their agglomeration. The presence of SiO2during high-temperature pyrolysis is proven crucial to create mesoporosity and a high BET area and pore volume in the N-doped carbon support (1780 m2g−1, 1.54 cm3g−1). This heterogeneous Co@mesoNC catalyst displays high activity and selectivity (>99%) for the selective hydrogenation of nitrobenzene to aniline at mild conditions (0.5–3 MPa, 343–383 K). When more challenging substrates (functionalized nitroarenes) are hydrogenated, the catalyst Co@mesoNC displays an excellent chemoselectivity to the corresponding substituted anilines. The presence of mesoporosity improves mass transport of reactants and/or products and the accessibility of the active Co-Nxsites, and greatly reduces deactivation due to fouling.