Mercury removal by Co3O4@TiO2@Fe2O3 magnetic core-shell oxygen carrier in chemical-looping combustion

Abstract Mercury pollution has received much attention due to its severe harm to human and ecological system. The major source of mercury emission is from coal combustion. In the flue gas, elemental mercury (Hg0) is the most abundant and difficult form to be removed. In the chemical-looping combustion of coal (CLCC), oxygen carrier (OC) plays the role of oxygen storage and release, and it also has catalytic ability for Hg0 removal. In this study, a magnetic material Co3O4@TiO2@Fe2O3 (CTF) with a core–shell structure was prepared by combining sol–gel and impregnation methods. The Co: Ti: Fe ratio was obtained as 1:2:4, which was optimized to achieve strong magnetism and catalytic ability. The Hg0 removal efficiency increased with the increase in temperature in the temperature range of 800–900 °C. The mercury removal efficiency of Hg0 + CTF + HCl was higher than that of Hg0 + HCl, indicating that CTF promoted the conversion of Hg0 to Hg2+/HgP. Both homogeneous and heterogeneous reaction pathways are important for Hg0 removal. CTF promotes the oxidation of Hg0 in HCl atmosphere by reacting with HCl to produce more Cl2, which is more reactive towards Hg0. Furthermore, Hg0 is adsorbed on CTF to form adsorbed Hg0 and HgO. Mercury on CTF is mainly desorbed in the form of HgO, which is beneficial for mercury removal. Ten redox cycles were applied on CTF, which still maintained a high Hg0 removal efficiency and strong magnetism. CTF can be used as a recycled OC in CLCC.