Development of LnMnO3+σ perovskite on low temperature Hg0 removal.

LnMnO3+σ (Ln = La, Pr, Nd, Sm, Eu, Gd or Dy) perovskites synthesized by sol-gel method were employed for gaseous elemental mercury (Hg0) removal from coal-fired flue gas. Characterization results revealed the structure of the perovskites presented a phase transition process from rhombohedral system to O- and O'-orthorhombic structure with the change of A-site rare earth elements. The perovskites showed satisfactory Hg0 removal capacity in a narrow temperature range of 100-150°C. NdMnO3+σ with an O-O' orthorhombic structure presented the best Hg0 removal performance, which markedly depends on four factors: crystal structure, oxygen vacancy density, Mn4+/Mn3+ ratio and surface element segregation. The Hg0 removal mechanism was illustrated based on the mercury temperature programmed desorption experiment and X-ray photoelectron spectroscopy characterization. Both chemisorption and catalytic oxidation played a role in the Hg0 removal process. Chemisorption dominated the Hg0 removal, due to the slow catalytic oxidation rate at low temperature. This work preliminarily established the relation between the structure of rare earth manganese perovskite and Hg0 removal performance.