Treatment of phenol by catalytic wet air oxidation: a comparative study of copper and nickel supported on γ-alumina, ceria and γ-alumina–ceria

Abstract

Cu, Ni, CuO and NiO catalysts, prepared by wet impregnation with urea and supported on γ-Al₂O₃, CeO₂, and Al₂O₃–CeO₂, were evaluated for Catalytic Wet Air Oxidation (CWAO) of phenol in a batch reactor under a milder condition (120 °C and 10 bar O₂). The synthesized samples, at their calcined and/or their reduced form, were characterized by XRD, H₂-TPR, N₂ adsorption–desorption, SEM-EDS and DR-UV-Vis to explain the differences observed in their catalytic activity towards the studied reaction. The influence of the support on the efficiency of CWAO of phenol at 120 °C and 10 bar of pure oxygen has been examined and compared over nickel and copper species. The SEM-EDS results reveal that the spherical crystalline Cu and Ni were successfully deposited on the surface of γ-Al₂O₃, CeO₂, Al₂O₃–CeO₂ within 16–90 nm and that they were highly homogeneously dispersed. It was found that catalysts prepared from impregnation solutions of Cu(NO₃)₂·3H₂O and Ni(NO₃)₂·6H₂O with urea addition had different textural characteristics and degrees of dispersion of Cu and Ni species. The urea addition in the traditional wet impregnation method was essential to improve the reducibility and degree of dispersion in Ni, and to a lesser extent, in Cu. According to the characterization analysis of H₂-TPR and UV-VIS RD a structure–activity relationship can be determined. The chemical oxygen demand (COD) and GC analyses confirmed the effect of calcined and reduced species for Cu and Ni applied to the catalytic oxidation of phenol, showing their significant impact in the final performance of the catalyst.