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

Abstract

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 NaBH4. Cu/WFA showed ~ × 105 times higher estimated rate constant kobs-p-NP/CCu (L min−1 gCu−1) compared with Cu/SiO2, Cu/Al2O3, 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/SiO2, Cu/Fe2O3/SiO2, 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 Had molecule, and that the reduction of Fe(III) to Fe(II) by NaBH4 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.