MOF-Templated Fabrication of Hollow Co₄N@N-Doped Carbon Porous Nanocages with Superior Catalytic Activity

Metallic Co₄N catalysts have been considered as one of the most promising non-noble materials for heterogeneous catalysis because of their high electrical conductivity, great magnetic property, and high intrinsic activity. However, the metastable properties seriously limit their applications for heterogeneous water phase catalysis. In this work, a novel Co-metal–organic framework (MOF)-derived hollow porous nanocages (PNCs) composed of metallic Co₄N and N-doped carbon (NC) were synthesized for the first time. This hollow three-dimensional (3D) PNC catalyst was synthesized by taking advantage of Co-MOF as a precursor for fabricating 3D hollow Co₃O₄@C PNCs, along with the NH₃ treatment of Co-oxide frames to promote the in situ conversion of Co-MOF to Co₄N@NC PNCs, benefiting from the high intrinsic activity and electron conductivity of the metallic Co₄N phase and the good permeability of the hollow porous nanostructure as well as the efficient doping of N into the carbon layer. Besides, the covalent bridge between the active Co₄N surface and PNC shells also provides facile pathways for electron and mass transport. The obtained Co₄N@NC PNCs exhibit excellent catalytic activity and stability for 4-nitrophenol reduction in terms of low activation energy (<i>E</i>_a = 23.53 kJ mol^–1), high turnover frequency (52.01 × 10²⁰ molecule g^–1 min^–1), and high apparent rate constant (<i>k</i>_app = 2.106 min^–1). Furthermore, its magnetic property and stable configuration account for the excellent recyclability of the catalyst. It is hoped that our finding could pave the way for the construction of other hollow transition metal-based nitride@NC PNC catalysts for wide applications