Adsorption and oxidation of elemental mercury over Ce-MnOx/Ti-PILCs

A series of innovative Ce-Mn/Ti-pillared-clay (Ce-Mn/Ti-PILC) catalysts combining the advantages of PILCs and Ce-Mn were investigated for elemental mercury (Hg0) capture at 100-350 °C in the absence of HCl in the flue gas. The fresh and used catalysts were characterized by scanning electron microscopy (SEM), nitrogen adsorption-desorption, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The catalyst characterization indicated that the 6%Ce-6%MnOx/Ti-PILC catalyst possessed a large specific surface area and high dispersion of Ce and Mn on the surface. The experimental results indicated that the 6%Ce-6%MnOx/Ti-PILC catalyst exhibited high Hg0 capture (>90%) at 100-350 °C. During the first stage of the reaction, the main Hg0 capture mechanism for the catalyst was adsorption. As the reaction proceeded, the Hg0 oxidation ability was substantially enhanced. Both the hydroxyl oxygen and the lattice oxygen on the surface of the catalysts participated in Hg0 oxidation. At a low temperature (150 °C), the hydroxyl oxygen and lattice oxygen from Ce4+→Ce3+ and Mn3+→Mn2+ on the surface contributed to Hg0 oxidation. However, at a high temperature (250 °C), the hydroxyl oxygen and lattice oxygen from Mn4+→Mn3+ contributed to Hg0 oxidation. Hg0 oxidation was preferred at a high temperature. The 6%Ce-6%MnOx/Ti-PILC catalyst was demonstrated to a good Hg0 adsorbent and catalytic oxidant in the absence of HCl in the flue gas.