Elemental mercury oxidation over manganese-based perovskite-type catalyst at low temperature

Abstract

La1−xSrxMnO3 (LSx, x=0/0.2/0.4/0.6) perovskite-type oxides catalysts were synthesized for elemental mercury (Hg0) oxidation in simulated coal-fired flue gas at low temperature. LS0.4 exhibited superior catalytic behavior for Hg0 oxidation at 100–200°C. The superior performance was mainly due to the surface adsorbed oxygen species in the catalysts. Effects of different components in the flue gas including HCl, O2, SO2, H2O, NO and NH3 on Hg0 oxidation efficiencies were studied. The results suggested that HCl significantly enhanced Hg0 oxidation efficiency in the presence of O2 and 10ppmv HCl was sufficient for enhancing the oxidation process. As the catalyst had strong oxygen storage capacity, the Hg0 oxidation activity was less dependent on O2 concentration. As a result, the catalyst could be applied in the power plants burning low-chlorine coals. SO2, H2O and NH3 had inhibitory effect on Hg0 oxidation, while NO enhanced it. SO2 could deactivate the catalyst and the deactivation was irreversible. In terms of mechanism, Hg0 oxidation with LSx could be explained by the suprafacial process (Langmuir–Hinshelwood mechanism) whereby reactive species from adsorbed flue gas components reacted with adsorbed Hg0. The catalyst also had potential for selective catalytic reduction (SCR) of NO with NH3 at low temperature, and the simultaneous removal of NO and Hg0 over LS0.4 was investigated. The NO and Hg0 conversion were higher than 50% and 85% when the space velocity was 40,000h−1, respectively. The results indicated that the catalyst might be used to remove NO and Hg0 simultaneously after the cold-side electrostatic precipitators in flue gas with low concentration of ash.