Preparation and characterization of CeO2/Al2O3 and its application on advanced treatment of wastewater

Ozone has been widely applied in the advanced wastewater treatment due to its high oxidation ability and environmental-friendly characteristics. However, the sole application of ozone in the removal of organic pollutants was limited by the problems such as large energy consumption, high selectivity and the tendency of the production of small molecular byproducts. By the application of catalyst, catalytic ozonation technology could promote the decomposition of ozone and produce hydroxyl radicals (·OH) with higher oxidation ability, which would make the thorough oxidation of organics possible. Compound catalysts such as CeO2-CuO2/Al2O3, CeO2/AC and CeO2-ZrO2 had been prepared by immersion method, hydro-thermal method and sol-gel method in the previous researches. These methods applied macromolecular organic polymers as the templates, which required high reaction temperature and strict operational conditions. Meanwhile, the application of these prepared catalysts was directed against the catalysis and decomposition of single organic pollutants. The rare earth element Cerium (Ce) is a kind of element with the highest natural abundance among lanthanide series metals. CeO2 has a strong redox ability and can speed up the decomposition of the ozone molecules and generate reactive free radicals ·OH. Due to its large specific surface area and good catalytic performance, Al2O3 has been widely adopted as an ideal carrier for catalyst. To improve the catalysis and oxidation performances of the ozonation system in the advanced treatment of wastewater, the doped CeO2/Al2O3 catalyst was prepared by using CeO2 and Al2O3 as active component and carrier, respectively. The catalyst was characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), nitrogen adsorption/ desorption isotherms and X-ray photoelectron spectroscopy (XPS). The performance of the CeO2/Al2O3 catalytic ozonation system for the advanced wastewater treatment was investigated by applying the secondary effluent from a real chemical wastewater treatment plant. The action mechanisms of the catalytic ozonation for the removal of organics were also analyzed. The results showed that the main active component of the catalyst was highly crystallized CeO2 with cubic fluorite structure and this structure remained after incineration processing. The dosage of CeO2 enhanced the dispersibility of Al2O3 and increased the pore volume and diameter, which resulted in a high specific surface area of 125 m2/g, a huge pore volume of 0.242 2 cm3/g and a pore diameter of 7.777 8 nm. The highest removal efficiency of chemical oxygen demand (COD) (42.8%) was obtained under the following conditions: influent COD concentration of 70-80 mg/L, catalyst dose of 110 g/L, ozone concentration of 18 g/m3 and pH value of 7.8, respectively. The removal efficiencies of COD remained higher than 40% after 5 repeated uses, which indicated that the catalyst was stable and could serve a relatively longer time. The coexistences of Ce(III) and Ce(IV) in the CeO2 speeded up the decomposition of ozone and more ·OH with higher oxidation ability were generated. The predominant reaction contributed to the removal of organics thus changed from direct ozone oxidation to ·OH oxidation. The results obtained in the present study demonstrated that the CeO2/Al2O3 catalyst had excellent catalytic characteristics and the catalytic ozonation system was promising in the advanced treatment of wastewater. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.