Structure–activity relationships, product species distribution and the mechanism of effect of multi-component flue gas on Hg0 adsorption and oxidation over CuO/ACs

Abstract

A series of Cu-doped activated cokes (CuO/ACs) were synthesized via an impregnation method and applied for the removal of elemental mercury (Hg⁰). Structure–activity relationships between Hg⁰ removal and CuO/AC surface characteristics were identified. Hg⁰ removal over CuO/AC occurs through a combination of physisorption and chemisorption and is mainly dominated by chemisorption. It was found that 1 nm micropores facilitate Hg⁰ physisorption. Hg⁰ could weakly adsorb onto an O-terminated crystal layer, whereas strongly adsorb onto Cu-terminated single highly dispersed, clustered and bulk CuO (110) crystal planes via the Mars–Maessen mechanism. Product distributions and mechanisms of Hg⁰ adsorption and oxidation over the CuO/AC catalyst under multi-component flue gases are also discussed. O₂ enhances both physisorption and chemisorption toward Hg⁰ by 38%. Inhibition of Hg⁰ removal by SO₂ originates from the competitive adsorption and deactivation of CuO cation vacancies, whereas the impact is weakened by O₂ through generating 20% of physically adsorbed mercury product species. NO and O₂ promote Hg⁰ chemisorption efficiency by 93% to form Hg(NO₃)₂. HOCl and/or Cl₂ produced by HCl can oxidize 100% of Hg⁰ to HgCl₂, and the catalytic oxidation efficiency is approximately 29%, but O₂ slightly lowers the Hg⁰ catalytic oxidation efficiency by 8%. The affinity ability between various flue gases and Hg⁰ follows the order O₂ < NO < HCl.