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 (Hg0) oxidation in the presence of HCl at the typical SCR reaction temperature of 350 °C. It was found that Hg0 oxidation activity of commercial SCR catalyst was significantly improved by the introduction of CuCl2. The X-ray fluorescence and Hg0 temperature-programmed desorption (Hg0-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 O2 at 350 °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 Hg0 oxidation. Hg0-TPD results suggested that the oxidized mercury compounds mainly exited as HgCl2 once HCl was present. The Hg0 oxidation mechanism over CuCl2-SCR catalyst in the presence of HCl could be explained as follows: The adsorbed Hg0 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.
The authors acknowledge financial supports by the Science and Technology Plan Project of Hebei Province of China (16273703D) and the Fundamental Research Funds for the Central Universities (2018MS118, 2017XS128).
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Conflict of interest
The authors declare no conflict of interest existed in this manuscript.
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