Porous carbon-encapsulated CuxO/Cu catalyst derived from N-coordinated MOF for ultrafast 4-nitrophenol reduction in batch and continuous flow reactors

Abstract

The preparation of reactors with high performance noble metal-free catalysts as the core is important research in catalytic hydrogenation. Herein, a novel multi-crystalline nitrogen-doped porous carbon-encapsulated CuxO/Cu Catalyst (CuxO/Cu/NC) was successfully synthesized by simple pyrolysis of N-coordinated metal organic frameworks (Cu2(BDC)2(DABCO)) and applied to construct a continuous flow reactor. The effects of N-coordination doping in MOF precursors on morphology, size and oxidation states of Cu species in the derived catalysts were systematically investigated by comparing with Cu/C (from Cu(BDC)) and Cu/NC (from Cu(BDC-NH2)). The significantly increased LUMO energy calculated by density functional theory (DFT) revealed that the introduction of coordination nitrogen-doped MOF precursor was beneficial to inhibit Cu2+ reduction during the calcination process and promote the formation of a carbon-supported multi-crystalline CuxO/Cu structure with rich defect sites and small size (13 nm). An enhanced catalytic activity was obtained for 4-nitrophenol (4-NP) reduction with the rate constant (k) of 0.1507 s−1, outperforming Cu/NC and Cu/C catalysts (5–11 folds), even many reported catalysts (1.2–95 folds). Ultrafast degradation of 4-NP was completed within 25 s. In addition, an online continuous flow reactor-high performance liquid chromatography system was also constructed, realizing real-time and automatic monitoring of the degradation reaction. It can remove 98.4 % of 4-NP within 50 s and maintain exceed 97 % degradation rate for 12 h. Highly dispersed catalyst, synergistic effect of copper species and the accelerated mass transfer endow the packed-bed reactor with superior activity and durability, it is expected to offer a great opportunity for contaminants reduction in water treatment.