(67f) RuO2/TiO2 Mercury Oxidation Catalyst for Mercury Emissions Control in Coal-Fired Power Plants

The new Mercury and Air Toxics Standards (MATS) rule was effective from 2012 and regulates mercury emissions from all commercial boilers starting from this year.  For coal-fired power plants burning lignite and sub-bituminous coals with low chlorine contents, the use of fuel additives such as CaBr₂ to boost halogen level then followed by either using activated carbon injection or optimization of SCR catalysts is a widely used mercury control solution.  However, there is a concern about the use of highly corrosive bromine additions, and is a need for a reduced loading.  In this study, we developed RuO₂ based catalyst using TiO₂ as support, that is highly active for Hg(0) oxidation while requiring very low bromine (less than 1 ppm in terms of HBr) at typical SCR unit temperatures of 350-400 °C.  Catalysts with different TiO₂ supports were tested and characterized by TEM, XRD, FTIR and chemisorption.  It was found that RuO₂ forms highly dispersed nano-particles and nano-layers on TiO₂ surface, resulting in high catalytic activity.  Selected catalysts were tested under typical simulated flue gas conditions for lignite and PRB coals.  The effects of various flue gas components such as SO₂, NOx, NH₃ and water vapor on Hg(0) oxidation were identified.  The catalyst can also work under bituminous coal flue gas conditions without bromine addition by utilizing only the chlorine species.  Any significant SO₃ or NO_x gas generation was not observed over the catalysts.  The RuO₂/TiO₂ mercury oxidation catalysts can be installed at the tail section of the existing SCR unit.  Oxidized mercury in the form of HgCl₂ or HgBr₂ is highly soluble in water and can be captured in the subsequent wet FGD process.