Deep co-removal of chlorobenzene and Hg0 from flue gas: CaO-SO2 synergy restores catalytic functionality via a poison-against-poison mechanism.

Municipal solid waste incineration flue gas often contains chlorobenzene (CB) and elemental mercury, yet practical removal is complicated by coexisting alkaline species (such as CaO) and SO2, which deactivate catalysts and pose risks from chlorinated by-products and mercury emissions. Herein, a three-dimensional porous CuO-modified CeO2-Al2O3 catalyst was prepared via a dual-templating method to investigate the simultaneous removal of CB and Hg0 following CaO and/or SO2 pretreatment, revealing an unexpected poison-against-poison mechanism between CaO and SO2 that restores deep oxidation capacity. The CaO and SO2 co-pretreated CuCeAl-Ca&S catalyst showed clear recovery of activity, achieving complete Hg0 removal from 250 to 400 °C and 64.4% CB conversion at 310 °C. Individually, CaO preferentially binds to Lewis acid sites on CuO, inhibiting CB and Hg0 adsorption/oxidation, while SO2 causes severe sulfation of Cu/Ce sites and three-dimensional framework collapse, leading to incomplete CB oxidation and chlorine deposition. In contrast, co-pretreatment with CaO and SO2 enables a poison-against-poison mechanism. CaO sacrificially reacts with SO2, preserving the three-dimensional framework and metal sites, while forming new Lewis and Brønsted acid sites, as well as Cu-Ov-CaSO4 interfacial active sites. These reconstructed sites restore C-Cl bond cleavage, ring opening and Hg0 oxidation, alleviating chlorinated by-products formation.