Superior Hg0 capture performance and SO2 resistance of Co-Mn binary metal oxide-modified layered MCM-22 zeolite for SO2-containing flue gas.

A Co-Mn binary metal oxide-modified layered MCM-22 zeolite was designed to capture gaseous elemental mercury (Hg0) from SO2-containing flue gas. The physicochemical properties of the Co-Mn/MCM-22 zeolite were characterized by XRD, FESEM, TEM, and XPS, and the results showed that MnO2 was highly dispersed on the surface and in the channel of MCM-22 zeolite. Co3O4 was loaded onto the surface of the MCM-22 zeolite via the stepwise ion exchange method to prevent SO2 poisoning of the MnO2 active site. The Hg0 removal efficiency increased from 54 to 83% at 300 °C with 10% Co loading on the 5% Mn/MCM-22 zeolite when 200 ppm of SO2 was introduced to the flue gas. The mechanism of Hg0 removal was mainly associated with catalytic oxidation and chemisorption. Mn4+ was the main active site for catalytic oxidation of Hg0 to Hg2+, and the surface adsorbed oxygen re-oxidized Mn3+ and combined with Hg2+ to form Hg-O-Mn, in which Mn acted as a bridge. Co3+ preferentially reacted with SO2 to form CoSO4, thereby protecting the Mn active sites for Hg0 capture. Therefore, Co-Mn/MCM-22 zeolite is a promising sorbent for the removal of Hg0 and SO2 resistance from SO2-containing flue gas.