Single-atom Ni encapsulated in N-doped porous carbon microspheres for enhanced catalytic transfer hydrogenation

Abstract

Catalytic transfer hydrogenation (CTH) represents a green and atom-economical strategy for organic transformations. However, the development of practical, high-performance catalysts—particularly for micron-scale systems suitable for industrial practice—remains a significant challenge. Herein, we report the rational synthesis of single-atom Ni-embedded, nitrogen-doped, hierarchically porous carbon microspheres (Ni@NHC) via a Pickering emulsion self-assembly strategy. The optimized catalyst, 1.3Ni@NHC-600, exhibits enhanced reactivity (1.25 mmolNBgcat−1h−1) and stability in the CTH of nitrobenzene and 1,2,3,4-tetrahydroquinoline, significantly outperforming both Ni nanoparticle-loaded nitrogen-doped carbon and metal-free NHC-600. Moreover, this catalyst demonstrates broad substrate compatibility across diverse nitroarenes and saturated N-heterocycles. Density functional theory calculations reveal that the single-atom Ni site in 1.3Ni@NHC-600 follows a CTH mechanism similar to that of the pyridinic-N site in NHC-600; nevertheless, the incorporation of single-atom Ni modifies the hydrogen atom transfer pathway in 1,2,3,4-tetrahydroquinoline. Specifically, the Ni-N4 site facilitates hydrogen transfer via a potential “push-pull” effect, thus markedly enhancing catalytic efficiency and affording high yields of aniline and quinoline. These findings provide mechanistic insights into the high reactivity of non-noble metal-doped carbon catalysts and establish a foundation for the rational design of efficient and practical CTH systems.