Primary amines and imines are important organic chemical raw materials and have a huge market share in the organic chemical industry. A new class of NiCx catalysts with carbon doping and controllable particle size has been developed by the research group of porous catalytic materials led by Guanghui Wang at Qingdao Institute of Energy, which exhibits excellent activity, selectivity and stability in the reductive amination of biomass-based carbonyl compounds for the preparation of primary amines and imines (Chinese Patent 202110919247.3), and the related research was published in ACS The study was published in the journal ACS Sustainable Chemistry & Engineering.

Primary amines and imines have a wide range of applications in the production of synthetic resins and plastics, adsorbents, dyes, fragrances, pharmaceuticals and cosmetics. Currently, the reductive amination process using carbonyl compounds to produce primary amines and imines is one of the most efficient routes in industry, but the process is prone to over-hydrogenation, resulting in low yields of primary amines and imines, difficult separation, and increased costs. The use of homogeneous catalysts can improve the selectivity of primary amines and imines, but the post-treatment process is complicated and the catalyst cost is high. In recent years, transition metal-based non-homogeneous catalysts have been widely used in reductive amination reactions, which have attracted much attention. However, the stability of metal-based catalysts is relatively poor in the corrosive reaction environment of reductive amination; the organic amines in the reactants and products tend to strongly adsorb on the surface of metal-based catalysts, resulting in reduced hydrogenation capacity of catalysts; in addition, the active sites of metal-based catalysts are subject to sintering, loss, oxidation and carbon accumulation during the catalyst recycling process, leading to catalyst deactivation. Therefore, there is still a great challenge to improve the stability of metal-based catalysts in reductive amination reactions.

The team firstly grew the hydrotalcite-like precursors in situ on the polymer surface using polymer spheres as the reducing agent, carbon source and size control agent, and then used the self-reduction method by roasting in an inert atmosphere to achieve the synthesis of the new NiCx catalysts, and prepared two catalysts with particle sizes of 7.5 nm (NiAl-10) and 47.5 nm (NiAl -5), respectively, and demonstrated that the selectivity of primary amines and imines can be directionally regulated by changing the particle size of the catalysts. In addition, due to the formation of Ni-Cx on the catalyst surface, the NiAl-10 and NiAl-5 catalysts were cycled for 10 times without deactivation and exhibited excellent catalytic stability, and the selectivities of both primary amines and imines were consistently greater than 99% during the cycling process. In addition, the NiAl-10 and NiAl-5 catalysts and the reductive amination system showed excellent performance for the reductive amination of a variety of carbonyl compounds and have good prospects for industrial applications.

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