(73a) Heterogeneous Elemental Mercury Oxidation Kinetics over RuO2/TiO2 Catalyst

We have developed a RuO₂/rutile TiO₂ catalyst, which is highly active for Hg(0) oxidation at typical SCR unit temperatures of 300-400 °C. In our previous study, the experimental evidence of dissociative HCl adsorption on the RuO₂/rutile TiO₂ catalyst surface under reaction conditions was obtained using an in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). In this study, heterogeneous Hg(0) oxidation kinetics over the RuO₂/rutile TiO₂ catalyst was investigated using a fixed-bed system in a temperature range of 300 to 400 °C under a steady-state condition. A kinetic model was developed based on our in-situ DRIFTS study results suggesting an Eley-Rideal mechanism and dissociative HCl adsorption in order to determine the reaction rate constant, activation energy, adsorption equilibrium constants and enthalpy of adsorption of HCl, NH₃ and SO₂. The activation energy value determined for the reaction was a low end value for the heterogeneous Hg(0) oxidation reaction using HCl gas reported in the literature, indicating the effectiveness of the RuO₂/rutile TiO₂ catalyst. The equilibrium adsorption analysis was used to determine the intrinsic reaction rate expression for Hg(0) oxidation kinetics with HCl under the competitive adsorption of NH₃ and SO₂. The kinetic expression could reasonably predict the Hg(0) oxidation performance under the competitive adsorption of NH₃ and SO₂ gases. The intrinsic kinetic expression obtained for the RuO₂/rutile TiO₂ catalyst is expected to be applicable to the design of an Hg(0) catalyst that can be installed at the tail end of a typical SCR unit.