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 similar to x 10(5) times higher estimated rate constant k(obs-p-NP)/C-Cu (L min(-1) g(Cu)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 H a d molecule, and that the reduction of Fe(III) to Fe(II) by NaBH4 can accelerate the reduction of Cu(11) 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. (C) 2019 Elsevier B.V. All rights reserved.