Mercury is a toxic and persistent pollutant that bio-accumulates in the food chain. Human exposure to mercury occurs primarily by consumption of contaminated fish. Mercury in the environment is transformed into more toxic methylmercury; consumption of methylmercury may cause neurotoxic effects. Children and particularly developing fetuses are especially susceptible to methylmercury effects. A USEPA proposed rule, Mercury and Air Toxics Standards, requires coal- and oil-fired power plants to use maximum available control technology to reduce the emissions of mercury and other hazardous air pollutants as of 2016. Among elemental, oxidized, and particulate-bound mercury species present in flue gas, elemental mercury (Hg(0)) is most difficult to control because of its low concentrations, low reactivity with other flue gas components via homogenous oxidation, and low solubility in water. This CAREER research plan will significantly advance the knowledge and fundamental mechanistic understanding of heterogeneous catalytic oxidation and adsorption using the reactions between Hg(0) vapor and transition metal chlorides. A detailed mechanistic study will be conducted to investigate the cyclic Deacon reaction involving transition metal chlorides for Hg(0) oxidation. Transition metal chlorides are proposed to be more effective in Hg(0) oxidation than metal oxides since they can readily eliminate the rate-limiting competitive HCl adsorption step. The reaction of Hg(0) with transition metal chlorides is a catalytic reaction such that chloride is consumed to form readily soluble and adsorbable HgCl2. The metal lowers the activation energy barrier for the oxidation reaction. This will lead to the further development of metal chloride-based modified selective catalytic reduction materials for simultaneous NOx reduction and Hg(0) oxidation, Hg(0)-specific catalysts, and sorbents.
This proposed research will enhance the capability to predict Hg(0) removal based on a fundamental understanding of physical and chemical principles. It will ultimately lead to advanced scientific knowledge and enhanced mercury control options needed for proposed mercury emission control regulations. It will also lead to various environmental remediation and separation technologies based on heterogeneous catalysis, adsorption, and absorption. The educational plan will provide co-benefits for chemical and environmental engineering faculty, students, and professionals in the areas of environmental catalysis, separation, and air quality/air pollution control. All of these efforts will ultimately increase awareness of mercury as a global pollutant and of best management practices for its control in flue gas emissions.
