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

Abstract

Catalytic conversion of elemental mercury (Hg(0)) 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 Hg(0) conversion at lower level HCl in flue gas, various catalysts supported on titanium dioxide (TiO(2)) and commercial SCR catalysts were investigated at various cases. Among the tested catalysts, ruthenium oxides (RuO(2)) not only showed rather high catalytic activity on Hg(0) oxidation by itself, but also appeared to be well cooperative with the commercial SCR catalyst for Hg(0) conversion. In addition, the modified SCR catalyst with RuO(2) displayed an excellent tolerance to SO(2) and ammonia without any distinct negative effects on NO(x) reduction and SO(2) conversion. The demanded HCl concentration for Hg(0) oxidation can be reduced dramatically, and Hg(0) oxidation efficiency over RuO(2) 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.

Oxidation Catalysts for Elemental Mercury in Flue Gases—A Review

“…Platinum Pt [8,37], palladium Pd [29,37], ruthenium oxide RuO 2 [36], and iridium Ir [38] have been tested on laboratory and pilot scale in order to determine their potential as mercury oxidation catalysts.…”

“…The tests involved the use of noble metal catalysts as powders, foil and coated on different supports, such as: alumina beads [37], alumina beads imbedded in fabric filters [29] and titania [36]. The role of the supports is to ensure a high dispersion of the noble metals, maximizing the contact area between flue gas components and the catalytic active centers responsible for the mercury oxidation reaction.…”

“…The published research on RuO 2 /TiO 2 catalysts pointed out that this system might be promising for mercury oxidation in coal-fired flue gases [36]. The lab scale investigation was conducted between 150 and 350 °C with most of the flue gas components present.…”

“…In the presence of SO 2 , no Cl 2 could be detected in the gas phase, although Hg oxidation showed only a small decrease. The authors presumed that under these conditions the formation of atomic Cl species still took place and that the mercury reacted with these species [36]. Temperature increased the oxidation rate.…”

“…One of the ways for enhancing Hg-oxidation activity is by applying/impregnating small quantities of metal oxides onto the SCR-DeNOx catalyst surface. Published studies reported results regarding Hg-oxidation activity of RuO 2 /SCR [36], CuO/SCR, NiO/SCR, ZnO/SCR [95].…”