Improvement of NH3 Resistance over CuO/TiO2 Catalysts for Elemental Mercury Oxidation in a Wide Temperature Range

Abstract In this study, the effects of ammonia (NH3) were explored for catalytic oxidation of elemental mercury (Hg°) over CeO2/TiO2, CuO/TiO2, Fe2O3/TiO2, and V2O5-WO3/TiO2 catalysts. In the presence of 50 ppm NH3, the results showed that CuO/TiO2 catalysts could still maintain 98-100% of Hg° conversion in the range of 100–400 °C, while the catalytic performance of other catalysts was significantly inhibited by NH3 in the same temperature range. NH3 resistance was observed on CuO/TiO2 catalysts. The catalysts were further characterized by means of XRD, H2-TPR, XPS, NH3-TPD, BET, and in-situ DRIFTS. For the CuO/TiO2 catalysts, Cu(II) was the primary Cu species that conducive to the reducibility properties. The strong reducibility properties of the catalysts were beneficial for the catalytic reaction. The mechanism of NH3 resistance in Hg° oxidation over CuO/TiO2 catalysts was proposed. At low-temperature range (lower than about 250 °C), abundant weak acidic sites contributed to the superior Hg° adsorption capacity. The Hg° oxidation activity was enhanced correspondingly. At high-temperature range (from about 250 to 400 °C), the Hg° oxidation performance was mainly affected by the oxidation of NH3. The main product of NH3 oxidation was NO2, which could promote Hg° oxidation activity.