Characteristics of commercial selective catalytic reduction catalyst for the oxidation of gaseous elemental mercury with respect to reaction conditions

The performance of $V_2O_5$/$TiO_2$-based commercial SCR catalyst for the oxidation of gaseous elemental mercury ($Hg^0$) with respect to reaction conditions was examined to understand the mechanism of $Hg^0$ oxidation on SCR catalyst. It was observed that a much larger amount of $Hg^0$ adsorbed on the catalyst surface under oxidation condition than under SCR condition. The activity of commercial SCR catalyst for $Hg^0$ oxidation was negligible in the absence of HCl, regardless of reaction conditions. The presence of HCl in the reactant gases greatly increased the activity of SCR catalyst for the oxidation of $Hg^0$ to oxidized mercury ($Hg^{2+}$) such as $HgCl_2$ under oxidation condition. However, the effect of HCl on the oxidation of $Hg^0$ was much less under SCR condition than oxidation condition. The activity for $Hg^0$ oxidation increased with the decrease of $NH_3$/NO ratio under SCR condition. This might be attributed to the strong adsorption of $NH_3$ prohibiting the adsorption of HCl which was vital species promoting the oxidation of $Hg^0$ on the catalyst surface under SCR condition.