Mechanism of Hg0 oxidation in the presence of HCl over a CuCl2-modified SCR catalyst

CuCl2-SCR catalysts prepared by an improved impregnation method were examined to evaluate the catalytic activity for gaseous elemental mercury (Hg-0) oxidation in the presence of HCl at the typical SCR reaction temperature of 350 degrees C. It was found that Hg-0 oxidation activity of commercial SCR catalyst was significantly improved by the introduction of CuCl2. The X-ray fluorescence and Hg-0 temperature-programmed desorption (Hg-0-TPD) methods were employed to characterize the catalysts. The results indicated that CuCl2 on CuCl2-SCR catalyst could release active Cl species in the presence of O-2 at 350 degrees C, and the released active Cl species could be replenished in the presence of gas-phase HCl. CuCl2-SCR catalyst possessed the appropriate active sites for the adsorption of NH3 and HCl, which could scavenge the inhibiting effect of NH3 on Hg-0 oxidation. Hg-0-TPD results suggested that the oxidized mercury compounds mainly exited as HgCl2 once HCl was present. The Hg-0 oxidation mechanism over CuCl2-SCR catalyst in the presence of HCl could be explained as follows: The adsorbed Hg-0 reacted with active Cl species released by CuCl2 to form HgCl2. The reduced CuCl was re-chlorinated to CuCl2 via the intermediate copper oxychloride (Cu2OCl2) formation by being exposed to the gas-phase HCl.