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

Abstract LaMnO3-based catalysts with perovskite structure have gained increasing interest for Hg0 oxidation owing to their excellent catalytic activity, high thermal stability and unique redox behavior. Understanding the Hg0 oxidation behavior on LaMnO3 will broaden the application of LaMnO3-based perovskites in Hg0 removal field. Density functional theory (DFT) calculations were conducted to examine the catalytic mechanism of Hg0 oxidation by HCl on LaMnO3 surface. The results indicate that Mn-terminated LaMnO3(010) surface is more active and stable than La-terminated surface. Hg0 and HgCl2 are chemisorbed on LaMnO3(010) surface. HgCl can be molecularly chemisorbed on LaMnO3(010) and serve as an intermediate in Hg0 oxidation reaction. HCl dissociatively adsorbs on LaMnO3(010) and generates surface active chlorine complexes. Langmuir–Hinshelwood mechanism, where the chemisorbed Hg0 reacts with the dissociatively adsorbed HCl, is responsible for Hg0 oxidation by HCl on LaMnO3(010). Catalytic Hg0 oxidation over the surface contains four-steps: Hg0 → 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).