Exploration of reaction mechanism between acid gases and elemental mercury on the CeO2–WO3/TiO2 catalyst via in situ DRIFTS

Abstract Although the oxidation of elemental mercury (Hg 0 ) on catalyst can be significantly affected by acid gases, its mechanism is still unclear. This study used in situ DRIFT to research the influence of acid gases (NO, HCl and SO 2 ) on the performance of mercury oxidation on catalyst CeO 2 (5)–WO 3 (9)/TiO 2 . The catalyst could capture a large amount of Hg 0 on the surface yet not oxidize all Hg 0 into gaseous oxidation mercury (Hg 2+ ) due to the limit of oxidation sites (CeO 2 ). The addition of NO and HCl improved the mercury oxidation efficiency because this process transformed the adsorbed mercury on the catalyst into gaseous Hg 2+ and formed new active sites. The in situ DRIFTS result indicated that NO 2 and nitrate served as active sites for mercury oxidation. The formation of active chlorine (Cl ∗ ) via HCl adsorption on the catalyst promoted the transformation of mercury into gaseous HgCl 2 . The NO and HCl addition could keep the mercury oxidation efficiency over 91.5% with the presence of 500–3000 ppm SO 2 and increase the SO 2 resistance of the catalyst. The reaction of NO and Hg 0 conforms to the Eley-Ridcal mechanism, while the reaction of HCl and Hg 0 follows the Languir-Hinshelwood mechanism.