Catalytically Active Co−N_x Species Stabilized on Nitrogen‐doped Porous Carbon for Efficient Hydrogenation and Dehydrogenation of N‐heteroarenes

Abstract

The development of bifunctional, highly active and stable non‐noble‐metal catalysts is important for synthetic chemistry. In this study, a highly dispersed Co catalyst stabilized on the mesoporous N‐doped carbon layers was prepared by adsorption and pyrolysis of cobalt complex on dendritic fibrous silica nanospheres (KCC‐1@Co−N−C−T). The characterizations of HAADF‐STEM, XRD and XPS together with the KSCN poisoning tests determine the absence of Co0 or CoOx nanoparticles and suggest that the Co−Nx species are the active sites. The formation of Co−Nx species results from the properties of N‐rich cobalt‐phenanthroline complex and dendritic fibrous silica supports, increasing the original spatial distance between Co atoms and thus preventing them from aggregation. The KCC‐1@Co−N−C‐800 catalyst showed excellent activity and selectivity for the oxidative dehydrogenation (ODH) of saturated N‐heterocycles and base‐free catalytic transfer hydrogenation (CTH) of unsaturated N‐heterocycles.

Single‐Atom Catalysis in Organic Synthesis

“…Xu et al instead synthesized Co SACs supported on spherical porous nanosilica, via pyrolysis of a metal-doped 1,10-phenanthroline ligand (Scheme 6). [37] This material was used for the oxidative dehydrogenation of heteroarenes using O 2 as an oxidant. The sample presented an excellent activity for the transfer hydrogenation of heteroarenes using formic acid as a reducing agent, with a turnover frequency (TOF) 25 times higher than that of the reference homogeneous catalyst.…”

Selective Hydrogenation of N-Heterocyclic Carboxylate over Nitrogen-Doped Porous Carbon-Supported Nano-Ni

“…Due to the high resonance stability of N -heterocyclic compounds and the potential toxicity to catalysts, the selective catalytic hydrogenation of N -heterocyclic compounds to saturated N -heterocyclic compounds is challenging compared with the hydrogenation of other aromatic compounds . As a result, most hydrogenation of this type is limited to polycyclic N -heteroaromatics, such as quinoline and quinoxaline, but a general method and a universal catalytic system for hydrogenation of N -heteroaromatics have not been formed yet, while the hydrogenation of pyridines is a major difficulty in particular . The many methods of synthesizing N -heterocyclic compounds can be roughly divided into chemical synthesis methods and partial hydrogenation methods. − However, because of the complex synthesis path, low product yield, high production cost, and large environmental pollution problems of chemical synthesis, partial hydrogenation is not only one of the most widely used methods in the field of organic synthesis but also involves many industrial applications, from the synthesis of fine chemicals to pharmaceutical chemicals. − It is one of the most preferred methods for the synthesis of N -heterocyclic compounds such as tetrahydroquinoline …”

“…Due to the high resonance stability of N-heterocyclic compounds and the potential toxicity to catalysts, the selective catalytic hydrogenation of N-heterocyclic compounds to saturated N-heterocyclic compounds is challenging compared with the hydrogenation of other aromatic compounds. 7 As a result, most hydrogenation of this type is limited to polycyclic N-heteroaromatics, 8 such as quinoline and quinoxaline, but a general method and a universal catalytic system for hydrogenation of N-heteroaromatics have not been formed yet, 9 while the hydrogenation of pyridines is a major difficulty in particular. 10 The many methods of synthesizing N-heterocyclic compounds can be roughly divided into chemical synthesis methods and partial hydrogenation methods.…”

“…36 Ma et al prepared a metal-free Co−N x catalyst by adsorption of the cobalt phenanthroline complex on the KCC-1 support and pyrolysis. 8 The catalyst KCC-1@Co-N-C-800T showed excellent activity and selectivity for the alkali-free catalytic transfer hydrogenation (CTH) of unsaturated Nheterocycles. In recent years, porous carbon materials have become another ideal metal carrier with excellent properties of high specific surface area, adjustable porosity, thermal stability, chemical stability, etc.…”

“…Commonly used materials such as silica, polymers, zeolite, alumina, and biosolid carriers have become excellent carrier systems. − Murugesan et al reported the preparation of novel supported Co/Co 3 O 4 core–shell nanoparticles by template synthesis of phthalic acid on silica and subsequent pyrolysis; these particles showed activity for the general hydrogenation of a variety of N -heteroaromatic hydrocarbons . Ma et al prepared a metal-free Co–N x catalyst by adsorption of the cobalt phenanthroline complex on the KCC-1 support and pyrolysis . The catalyst KCC-1@Co-N-C-800T showed excellent activity and selectivity for the alkali-free catalytic transfer hydrogenation (CTH) of unsaturated N -heterocycles.…”