N-doped hollow carbon nanospheres encapsulating Ni nanoparticles: Modulating the surface microenvironment for efficient selective hydrogenation

Catalytic hydrogenation enables the selective conversion of phenol into high-value products such as fuels and chemicals, contributing directly to sustainable chemistry and the utilization of renewable resources. In this study, Ni nanoparticles encapsulated in hollow carbon nanospheres with tailored surface microenvironments were synthesized by modulating the nitrogen doping pattern, carbon layer thickness, and metal loading position. These catalysts were applied to the selective hydrogenation of phenol. Characterization and experimental results revealed that in-situ nitrogen doping optimizes the chemical microenvironment of the catalysts by participating in the formation of catalyst precursors, which is reflected in the abundant defect structures, strong metal-support interactions, and high concentration of active Ni0 sites. The influence of the physical microenvironment was further investigated by adjusting the carbon shell thickness and the location of nickel loading. The Ni@NHCs catalyst with a moderate carbon layer thickness maintains a complete spherical morphology without increasing the mass transfer resistance of reactants, thereby offering a favorable structural foundation for the selective hydrogenation of phenol. Compared with externally loaded nickel catalysts, the internally encapsulated Ni nanoparticles exhibit smaller particle sizes and higher metal dispersion. Under the reaction conditions of 130 °C for 1 h, the Ni@NHCs catalyst achieved 99.68% phenol conversion and 99.79% selectivity for cyclohexanol. Moreover, the catalyst retained high activity after seven reuse cycles, and its hollow structure remained intact after the reaction. This work provides a sustainable catalytic solution for the selective hydrogenation of phenol.