COMBINED MERCURY REMOVAL AND LOW TEMPERATURE NH 3 -SCR OF NO WITH MnO x /TiO 2 SORBENTS/CATALYSTS

MnO x /TiO 2 catalysts/sorbents were investigated for flue gas purification via the simultaneous low-temperature NH 3 -SCR of NO and elemental Hg capture, in the temperature range 25-300 °C. In particular, the effects of the Mn precursor salt (acetate vs. nitrate) and of the TiO 2 textural properties (nanotubes vs. random mesopores) on both deNO x and Hg capture efficiencies were addressed. The catalysts/sorbents were also characterized by means of ICP- MS, XRD, BET, H 2 -TPR, NH 3 adsorption, and TPD of both NH 3 and Hg. Catalysts prepared by acetate precursors generally displayed a higher reducibility and oxidation activity, which was beneficial to improve mercury capture rate, but adversely impacted on the selectivity of the SCR process at temperatures above 150 °C. In the absence of HCl in the flue gas, Hg was effectively captured up to 250 °C and stored on the catalysts, most probably in an oxidized form. The original sorption properties of the catalysts could be fully restored by a simple thermal treatment at temperatures between 400-500 °C, releasing elemental mercury. The use of TiO 2 nanotubes as the support for the MnO x active phase increased the strength of the Hg bond.