Manganese bridge of mercury and oxygen for elemental mercury capture from industrial flue gas in layered Mn/MCM-22 zeolite

Mn-based oxides have been confirmed to possess gaseous elemental mercury (Hg-0) uptake performances. One strategy for Mn-based oxides designing was taking full advantage of surface oxygen to bond surface oxidized mercury. In this study, Mn modified layered MCM-22 zeolite were prepared to get a high dispersion of Mn active sites. The composites were characterized and the results showed that the highly dispersed MnOx particles could be readily deposited on the surface and in the channel of layered MCM-22 zeolite. The results showed 5% Mn/MCM-22 zeolite had a Hg-0 removal efficiency of 92% and adsorption capacity of 0.32 mg/g at 300 degrees C under 5% O-2. The mechanism of Hg-0 removal is mainly associated catalytic oxidation and chemisorption. Mn4+ is the main active site for Hg-0 catalytic oxidation to Hg2+, and Mn4+ is only reduced to Mn3+, some of which is reoxidized to Mn4+ by active oxygen. The Hg2+ combines with oxygen and form HgO absorbed in the pores of Mn/MCM-22 zeolite. The distribution of Hg elemental was better coincident with Mn elemental which further verified the role of Hg-O-Mn, in which Mn played the role of bridge. Therefore, Mn/MCM-22 zeolite is a promising sorbent for Hg-0 removal from flue gas.

Automated summary

This study successfully prepared modified layered MCM-22 zeolite with highly dispersed Mn active sites for efficient removal of gaseous elemental mercury (Hg-0). The mechanism of Hg-0 removal mainly involves catalytic oxidation and chemisorption on Mn active sites, with Mn playing a bridging role between Hg and O in the pores of Mn/MCM-22 zeolite. The promising Mn/MCM-22 zeolite composite demonstrates high potential as a sorbent for Hg-0 removal from flue gas.