Cobalt Nanoparticles Encapsulated in Nitrogen-Doped Carbon Shells: Efficient and Stable Catalyst for Nitrobenzene Reduction

In this work, cobalt nanoparticles@N-doped carbon nanocomposites (Co@NC) with controllable Co contents have been prepared by pyrolysis of Zn/Co bimetal zeolitic imidazolate framework-9 (Zn/Co-ZIF-9). The magnetic cobalt nanoparticles encapsulated by multilayered carbon shells are uniformly distributed on the NC substrates. The as-obtained Co@NC 45.8 wt % samples exhibit higher catalytic activity and stability for the heterogeneous catalytic reduction of nitrobenzene to anilines by NaBH4 under gentle condition. The reduction reaction over Co@NC 45.8 wt % catalysts accords with pseudo-first-order kinetics with an apparent rate constant of 0.844 min–1 and apparent activation energy of 14.20 kJ/mol at room temperature. Additionally, the related catalytic mechanism and reaction path have been fully explored and it has been found that the active hydrogen species induced by metallic cobalt nanoparticles, instead of the self-hydrolysis of NaBH4, accounts for the efficient reduction of nitrobenzene. Moreover, the Co@NC catalysts are greatly expedient for the separation and recycling from the reaction system due to its ferromagnetism, suggesting the promising application in the catalytic reduction reaction of nitrobenzene into anilines.