Multi-Crystalline N-doped Cu/CuxO/C Foam Catalyst Derived from Alkaline N-coordinated HKUST-1/CMC for Enhanced 4-Nitrophenol Reduction

Abstract Multi-crystalline N-doped Cu/CuxO/C foam catalysts are successfully synthesized from N-coordinated HKUST-1/cellulose and applied in 4-nitrophenol (4-NP) reduction. Effects of N content and basicity on Cu morphology, crystal lattice and size, component dispersion and oxidation states in catalysts are systematically investigated. Moreover, transforming powder catalysts to foam morphology is proposed to further enhance catalytic performance and facilitate more feasible industrial applications. Results reveal that alkaline N-dopant simultaneously inhibits the growth of Cu crystals to only 3–5 nm and restrains Cu(II) reduction in HKUST-1 during calcination. This facilitates the formation of a special multi-crystalline Cu/Cu2O/CuO structure. Furthermore, Cu2O species on catalyst surface increase with increasing alkaline strength and N dopant content. Graphitic nano-structure catalyzed by Cu sites in HKUST-1 greatly enhances electron transfer in 4-NP reduction leading to 21 times faster kinetics and better recycle performance by melamine-doped Cu/CuxO/C foam catalyst than bare Cu/C catalyst directly from HKUST-1. Moreover, carbon foam derived from CMC can further amplify Cu dispersion and inhibit its agglomeration, thus promotes catalyst stability during cycling performance. Therefore, the proposed in-situ N doping and foam shaping strategy can efficiently enhance catalytic activity and reaction stability for 4-NP reduction, which can be envisaged of potential value for other similar industrial catalysis.