Catalytic wet air oxidation of an aqueous solution, bisphenol A (BPA), was carried out at 160 °C and at 20 bar of air in a batch reactor. Silver catalysts (2.5 wt%) prepared by wet impregnation and complexation on commercial CeO2 in addition to Ce0.85Zr0.15O2 and Ce0.2Zr0.8O2 sol–gel mixed oxides were synthesized and used as catalysts in the reaction. Characterizations of the catalysts were performed by using FESEM, XRD, BET, XPS and ICP–OES techniques. Residual BPA concentration was analyzed by using an UV–Vis technique and organic compound content was measured via the total organic carbon method. Commercial CeO2 showed a smaller specific surface area and a larger crystallite size than laboratory prepared Ce–Zr mixed oxides. The highest BPA removal (76 %) was achieved after 3 h with CeO2, Ce0.85Zr0.15O2 and Ag/Ce0.85Zr0.15O2 catalysts revealing that the addition of silver had no effect on the catalytic activity of the pure supports. However, the loading of active metal to the supports by complexation decreased the adsorption of the BPA during the heating period and hence the Ag/Ce0.85Zr0.15O2 prepared via complexation was the most active catalyst with only 1 % adsorption of BPA. Moreover, the activity of the catalysts was not related to the surface area of the samples. According to the ICP–OES analysis of the terminal water samples, leaching of the silver was occurred during oxidation experiments explaining the behavior of Ag catalysts in the reaction.
CWAO BPA Silver Cerium Zirconium XPS
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The authors gratefully acknowledge the Academy of Finland for providing research funding, AOPI project (263397) within the research program for Sustainable Governance of Aquatic Resources (AKVA). Centre of Microscopy and Nanotechnology at the University of Oulu, Finland is also acknowledged for its research facilities in XPS analysis.