Supported Ni⁰@C-N catalyst with dual-reaction surfaces: Structure-performance relation in the selective hydrogenation of p-chloronitrobenzene

How to break the activity-selectivity dependence in halonitrobenzene hydrogenation remains a challenge. In this work, Ni@C-N/SiO2 were synthesized and examined in the hydrogenation of p-chloronitrobenzene. It showed that the electron transferred from nitrogen doped carbon shell to Ni-0 core (core-shell synergistic effect) dominated the intrinsic activities of Ni@C-N/SiO2 with dual-reaction surfaces (H-2 dissociated on Ni-0 core, while p-chloronitrobenzene was hydrogenated on carbon shell) in the thiophene-free hydrogenation, leading to their higher turnover frequencies than Raney Ni catalyst. During the thiophene-involved hydrogenation, the adsorption of thiophene on Ni-0 changed its electron density and blocked the active sites. These enhanced the selectivity, but significantly reduced the activity for Raney Ni catalyst. Comparatively, the carbon shell protected Ni-0 core from thiophene adsorption so that the hydrogen dissociated on Ni-0 as usual. However, the adsorption of thiophene on the carbon shell reduced the available sites for p-chloronitrobenzene adsorption. Although Ni@C-N/SiO2 had lower activities in the thiophene-involved reactions than those of thiophene-free reactions, they achieved similar to 100 % p-chloroaniline selectivities and 8-fold higher turnover frequencies than Raney Ni, breaking the activity-selectivity dependence. This reveals that the available sites on the carbon shell and the core-shell synergistic effect determine the thiophene-involved hydrogenation activities of Ni@C-N/SiO2 catalysts.