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

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 SO2) on the performance of mercury oxidation on catalyst CeO2(5)-WO3(9)/TiO2. The catalyst could capture a large amount of Hg-0 on the surface yet not oxidize all Hg-0 into gaseous oxidation mercury (Hg2+) due to the limit of oxidation sites (CeO2). The addition of NO and HCl improved the mercury oxidation efficiency because this process transformed the adsorbed mercury on the catalyst into gaseous Hg2+ and formed new active sites. The in situ DRIFTS result indicated that NO2 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 HgCl2. The NO and HCl addition could keep the mercury oxidation efficiency over 91.5% with the presence of 500-3000 ppm SO2 and increase the SO2 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.