Synergistic effect of Cu loading on Fe sites of fly ash for enhanced catalytic reduction of nitrophenol

A novel Cu catalyst was developed using water-washed coal fly ash (WFA) as a support material for catalytic reduction of p -nitrophenol ( p -NP) in the presence of NaBH 4 . Cu/WFA showed ~ × 10 5 times higher estimated rate constant k obs-p-NP /C Cu (L min −1  g Cu −1 ) compared with Cu/SiO 2 , Cu/Al 2 O 3 , and other Cu catalysts previously reported. Surprisingly, we obtained a significant lower price value (Price’/K) (0.027–0.068 USD/L min −1 ) for Cu/WFA in comparison with other Cu catalysts and precious metallic catalysts (Pd, Au, Ag, and Pt). Various surface analyses and additional experiments using Fe/SiO 2 , Cu/Fe 2 O 3 /SiO 2 , and Cu/HCl-treated WFA demonstrated that Cu(0) nanoparticles were well loaded on the surface of WFA, where Fe elements were abundant, resulting in a dramatic enhancement of the Cu/WFA catalytic activity . Particularly, X-ray photoelectron spectroscopy revealed the abundance of Cu(0)/Fe(III) and Cu(0)/Fe(II) in the WFA surface. This indicates that Cu(0) was the main driving force for the activation of H ad molecule, and that the reduction of Fe(III) to Fe(II) by NaBH 4 can accelerate the reduction of Cu(II) to Cu(0). Recycling and phytotoxicity tests showed that Cu/WFA can be applied as a reusable catalyst with low environmental impact, revealing the remarkable potential of non-precious metal/WFA catalyst in the field of environmental remediation.