Significance of RuO2 Modified SCR Catalyst for Elemental Mercury Oxidation in Coal-fired Flue Gas

Abstract

Catalytic conversion of elemental mercury (Hg⁰) to its oxidized form has been considered as an effective way to enhance mercury removal from coal-fired power plants. In order to make good use of the existing selective catalytic reduction of NO_x (SCR) catalysts as a cobenefit of Hg⁰ conversion at lower level HCl in flue gas, various catalysts supported on titanium dioxide (TiO₂) and commercial SCR catalysts were investigated at various cases. Among the tested catalysts, ruthenium oxides (RuO₂) not only showed rather high catalytic activity on Hg⁰ oxidation by itself, but also appeared to be well cooperative with the commercial SCR catalyst for Hg⁰ conversion. In addition, the modified SCR catalyst with RuO₂ displayed an excellent tolerance to SO₂ and ammonia without any distinct negative effects on NO_x reduction and SO₂ conversion. The demanded HCl concentration for Hg⁰ oxidation can be reduced dramatically, and Hg⁰ oxidation efficiency over RuO₂ doped SCR catalyst was over 90% even at about 5 ppm HCl in the simulated gases. Ru modified SCR catalyst shows a promising prospect for the cobenefit of mercury emission control.