Efficient removal of Hg⁰ from cement kiln flue gas using Ce_xFe_yO_z composite catalyst

In this study, a kind of Ce_xFe_yO_z composite with oxygen vacancy structure and strong oxygen storage capacity was prepared by coprecipitation method. Under the condition of no HCl of flue gas, the Hg⁰ in the flue gas of cement kiln was efficiently and economically removed by using 6-8% oxygen. The results showed that the optimum preparation conditions of the catalyst were Ce-Fe molar ratio of 1-11 and calcination temperature of 550 °C. In addition, the reaction temperature, space velocity, the concentration of O₂, SO₂, and NO had significant effects on the removal efficiency of Hg⁰ at different rates. More precisely, at the reaction temperature of 350 °C, low airspeed, high concentration of O₂, and low concentration of SO₂ and NO, the efficiency reached the highest value. According to XPS results, the elemental valence of the Ce_xFe_yO_z composite changed after the reaction. The redox pairs of Ce³⁺-Ce⁴⁺ and Fe³⁺-Fe²⁺ had the ability to transfer electrons, which enabled more oxygen adsorbed on the catalyst surface to be converted into O₂^-, leading to the improvement of the oxidation efficiency of Hg⁰.