Designing and synthesizing high-efficiency non-precious metal-based catalysts having uniform active sites increases the reactivity and selectivity of materials and provides a platform for an in-depth understanding of their catalytic reaction mechanism. In this study, we provided an approach for fabricating isolated nickel single-atom sites (Ni SAs) with high loading (4.9 wt.%) stabilized on nitrogen-doped hollow carbon spheres (NHCS) using a core–shell structured Zn/Ni bimetallic zeolitic imidazolate framework (ZIF) composite as the sacrificial template. The as-fabricated Ni SAs/NHCS catalyst shows superior activity, selectivity, and recycling durability for the catalytic transfer hydrogenation of nitrobenzene to aniline, thus achieving 100% yield of aniline with a turn-over frequency (TOF) value as high as 29.9 h⁻¹ under mild conditions. This TOF value is considerably superior to the supported Ni nanoparticle catalysts. The experiments designed show that the hollow structure feature of NHCS facilitates accessible active sites and mass transfer, which thus contributes to the enhancement of the catalytic performance of Ni SAs/NHCS. Density functional theory calculations show the high chemo-selectivity and activity of the Ni SAs catalyst, arising from the unique role of the single Ni-N₃ site on simultaneously activating the H donor (N₂H₄) and substrate, as well as the hydrogenation of the –NOH group as the rate-determining step.

Enhancing the selectivity of noble metal catalysts through electronic modulation is important for academic research and chemical industrial processes. Herein, we report a facile sacrificial template strategy for the synthesis of PdZn intermetallic compound (3–4 nm) highly distributed in ZnO/nitrogen-decorated carbon hollow spheres (PdZn-ZnO/NCHS) to optimize the selectivity of Pd catalysts, which involves carbonization of a core–shell structured polystyrene (PS)@ZIF-8 precursor in an inert atmosphere, impregnation Pd precursor, and subsequent H₂ reduction treatment. Due to the unique structural and compositional features, the developed PdZn-ZnO/NCHS delivers an excellent catalytic performance for the semihydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE) with high activity (> 99%), high selectivity (96%), and good recyclability, outperforming the analog Pd on ZnO (Pd/ZnO) as well as the supported Pd nanoparticles (Pd/C and Pd/NC). Density functional theory (DFT) calculations reveal that the presence of Zn^δ+ species in PdZn-ZnO/NCHS alters the adsorption modes of reactant and product, leading to a decrease of the adsorption strength and an enhancement of the energy barrier for overhydrogenation, which results in a kinetic favor for the selective transformation of MBY to MBE. In addition, PdZn-ZnO/NCHS was also very effective for the partial hydrogenation of dehydrolinalool to hydrolinalool.