Nitrogen-doped porous carbon-encapsulated copper composite for efficient reduction of 4-nitrophenol

Developing low-cost non-precious metals as efficient catalysts for the reduction of toxic 4-nitrophenol (4-NP) to useful 4-aminophenol (4-AP) have received increasing attention in recent years. Herein, a novel and efficient Cu-based catalyst Cu/Cu_xO@CN (carbon doped with nitrogen) was prepared via a facile method from pyrolysis of bi-ligand MOFs material Cu₂(BDC)₂(BPY) (BDC = p-Phthalic acid, BPY = 4,4'-bipyridyl) in Ar atmosphere. Characterization results revealed that N doping in carbon matrix favors the development of mesoporous structure, the formation of more defect sites in carbon matrix, better dispersion of Cu/Cu_xO nano particles, and maintenance of Cu species in metallic Cu state (the active site), all of which contribute to a superior catalytic activity for 4-NP reduction with a pseudo-first-order rate constant as high as 0.126 s^-1 (the molar ratio of NaBH₄ to 4-NP is 400), nearly 11 times higher than its counterpart Cu/Cu_xO@C without N doping (0.011 s^-1). The activation energy for 4-NP reduction to 4-AP catalyzed by Cu/Cu_xO@CN was determined as 55.6 kJ mol^-1 (the molar ratio of NaBH₄ to 4-NP is 100). In addition, Cu/Cu_xO@CN showed excellent reusability in successive 6 cycles. The facile synthesis and superior catalytic activity make Cu/Cu_xO@CN a promising catalyst in industrial applications for many other similar reaction systems.