The Preparation And Performance Of Mn And Co Metal Oxide Catalyst For Elemental Mercury Removal From SFG

The mercury pollution in atmospheric environment is a global problem that has caused widespread concern in the world. In recent decades, many countries, especially in the developed countries, have taken steps to reduce mercury uses and releases. Coal-fired power plants are major anthropogenic sources of mercury emissions. Mercury in coal is released in three forms: elemental(Hg0), oxidized(Hg2+) and particulate-bound(Hgp). As compared with Hg2+ and Hgp, Hg0 is very difficult to control from the flue gas due to its high volatility and low solubility in water. In this work, we focus on the development of gaseous Hg0 oxidation catalyst. The effects of precursor, active content, support, reaction temperature preparation method and flue gas compositions et al. on the removal of Hg0 were investigated to obtain the one catalyst with high activity and high resistance of SO2 and water.The characterizations of the catalysts were analyzed using many methods. The in-depth study of the reaction mechanism provide a theoretical basis for further improvement of the catalyst. The novelties and important conclusions of this work are summarized as follows:(1) Elemental mercury(Hg0) catalytic oxidation removal from simulated flue gas were carried out by using the MnOx/Al2O3 catalysts prepared by the wet impregnation method. The result showed that the catalyst prepared with manganese nitrate exhibited higher Hg0 removal efficiency than catalyst prepared with manganese acetate, and the surface morphology and species form of were the main factor for getting an excellent Hg0 removal efficiency. For the MnOx/Al2O3 catalyst, the optimal reaction temperature and calcination temperature were 150 and 400℃ ℃, respectively. The oxygen from the flue gas, which replenished the lattice oxygen of the catalyst consumed, can promote the catalytic oxidation of Hg0. To some extent NO, SO2 and H2 O displayed inhibitory effects on Hg0 removal. The influence of SO2 was maximum, H2 O followed and NO minimum. While in the absence of oxygen, NO promote mercury removal.(2) CoxMnyTi catalysts synthesized by a deposition-precipitation method were employed to oxidize gas-phase elemental mercury(Hg0) without the aid of HCl at low temperature on a laboratory-scale fixed-bed reactor. The results showed that the addition of Mn and Co significantly enhanced the efficiency of Hg0 oxidation, which is because the presence of Co led to a better dispersion of Mn over TiO2 and the MnOx changed to be amorphous species. With optimal loading value of 6 % Co species on Mn30 Ti, the Hg0 oxidation efficiency could reach around 98 % at 150 ℃. In comparison with pure N2 atmosphere, the presence of NO can slightly promote the oxidation of Hg0. The effects of SO2 and H2 O with lower concentrations were insignificant. However, when SO2 further increased above 1000 ppm, a seriously inhibitory influence on Hg0 oxidation was observed.(3) A series of studies on the performance of elemental mercury(Hg0) catalytic oxidation removal from simulated flue gas were carried out using the Mn-Co/MCM-41 catalysts prepared by the wet impregnation method. The results showed that the addition of Mn and Co significantly enhanced the efficiency of Hg0 oxidation. With a Mn/Co molar ratio of 3:1, the Hg0 oxidation efficiency of the catalyst exhibited as high as 90% at 150 ℃. Compared with the single Mn or Co modified catalysts, the presence of Co can not only lead to a better dispersion of Mn and Co over MCM-41 but also promote the conversion of Mn3+ to Mn4+ and the enhancement of reduction ability, which would play an important role in the promotion of Hg0 oxidation.