Efficient mercury removal in chlorine-free flue gas by doping Cl into Cu₂O nanocrystals

The low content of hydrogen chloride (HCl) in flue gas is difficult to meet the request of Hg⁰ removal. Here, a small amount of Cl was doped into the crystal lattice of Cu₂O nanocrystals (Cl-Cu₂O), presenting excellent Hg⁰ removal efficiency in chlorine-free coal combustion flue gas. SEM, XRD, BET, and XPS characterizations revealed well crystal morphology and structure of Cl-Cu₂O catalyst. Besides, Cl-Cu₂O had smaller sizes and higher BET surface area compared with Cu₂O. Hg⁰ removal behaviors were studied using a lab-scale fixed-bed reactor. After doping Cl, Hg⁰ removal efficiency was improved obviously and could reach nearly 100% above 150 ℃, indicating chlorine incorporated into the catalyst lattice had a better role for Hg⁰ removal. Besides, gas composition effect on Hg⁰ removal was analyzed. Cl-Cu₂O had high sulfur resistance capacity, and Hg⁰ removal efficiency can still reach above 90% even at 2000 ppm SO₂. O₂ played a critical role in the Hg⁰ removal reaction. Furthermore, a plausible mechanism for Hg⁰ removal was analyzed. Doping Cl into the lattice of Cu₂O nanocrystals was beneficial for the activation of molecular oxygen, and generated reactive oxygen species can further activate Cl to participate in the Hg⁰ removal reaction.