Insights into the catalytic behavior of LaMnO3 perovskite for Hg0 oxidation by HCl

LaMnO3-based catalysts with perovskite structure have gained increasing interest for Hg-0 oxidation owing to their excellent catalytic activity, high thermal stability and unique redox behavior. Understanding the Hg-0 oxidation behavior on LaMnO3 will broaden the application of LaMnO3-based perovskites in Hg-0 removal field. Density functional theory (DFT) calculations were conducted to examine the catalytic mechanism of Hg-0 oxidation by HCl on LaMnO3 surface. The results indicate that Mn-terminated LaMnO3(010) surface is more active and stable than La-terminated surface. Hg-0 and HgCl2 are chemisorbed on LaMnO3(010) surface. HgCl can be molecularly chemisorbed on LaMnO3(010) and serve as an intermediate in Hg-0 oxidation reaction. HCl dis-sociatively adsorbs on LaMnO3(010) and generates surface active chlorine complexes. Langmuir-Hinshelwood mechanism, where the chemisorbed Hg-0 reacts with the dissociatively adsorbed HCl, is responsible for Hg-0 oxidation by HCl on LaMnO3(010). Catalytic Hg-0 oxidation over the surface contains four-steps: Hg-0 -> Hg(ads) -> HgCl(ads) -> HgCl2(ads) -> HgCl2, and the second step (Hg(ads) -> HgCl(ads)) is the rate-determining step because of its relatively larger energy barrier (0.74 eV).