(617gb) Elemental Mercury Oxidation Mechanism over RuO2/TiO2 Catalyst: An in-Situ FTIR Study

Authors: 
Liu, Z., University of Cincinnati
Sriram, V., University of Cincinnati
Lee, J. Y., University of Cincinnati

We have developed a RuO2/ TiO2 catalyst, which is highly active for Hg(0) oxidation at typical SCR unit temperatures of 350-400 °C. Currently, the knowledge of heterogeneous mercury oxidation mechanisms over metal oxides is very limited. It is generally believed that surface halogen species are responsible for mercury oxidation, but no experimental evidence of these active species has been reported so far. In this study, in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) was used to probe mercury oxidation mechanisms over the RuO2/TiO2 catalyst. It was found that when the catalyst is exposed to HCl gas, HCl will dissociate on the catalyst surface to form Ru-H and Ru-Cl bonds. Although Ru-Cl in the far infrared region is difficult to detect due to the low energy nature of far infrared, Ru-H vibration in the mid-range infrared can be used as an indicator of Ru-Cl because of the 1:1 ratio of H and Cl atoms in HCl. The use of deuterium chloride (DCl) proved that the Ru-H bond only comes from H atom in HCl and not from other hydrogen containing molecules such as water vapor or ammonia. In-situ DRIFTS demonstrated that surface chlorine is responsible for mercury oxidation and its concentration is negatively affected by ammonia and sulfur dioxide gases, which is in agreement with the inhibition effects of these gases observed during the performance tests. Based on these findings, a heterogeneous mercury oxidation mechanism is proposed.
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