MnO_<i>x</i>/Graphene for the Catalytic Oxidation and Adsorption of Elemental Mercury

Abstract

MnO_<i>x</i>/graphene composites were prepared and employed to enhance the performance of manganese oxide (MnO_<i>x</i>) for the capture of elemental mercury (Hg⁰) in flue gas. The composites were characterized using FT-IR, XPS, XRD, and TEM, and the results showed that the highly dispersed MnO_<i>x</i> particles could be readily deposited on graphene nanosheets via hydrothermal process described here. Graphene appeared to be an ideal support for MnO_<i>x</i> particles and electron transfer channels in the catalytic oxidation of Hg⁰ at a high efficiency. Thus, MnO_<i>x</i>/graphene-30% sorbents exhibited an Hg⁰ removal efficiency of greater than 90% at 150 °C under 4% O₂, compared with the 50% removal efficiency of pure MnO_<i>x</i>. The mechanism of Hg⁰ capture is discussed, and the main Hg⁰ capture mechanisms of MnO_<i>x</i>/graphene were catalytic oxidation and adsorption. Mn is the main active site for Hg⁰ catalytic oxidation, during which high valence Mn (Mn⁴⁺ or Mn³⁺) is converted to low valence Mn (Mn³⁺ or Mn²⁺). Graphene enhanced the electrical conductivity of MnO_<i>x</i>, which is beneficial for catalytic oxidation. Furthermore, MnO_<i>x</i>/graphene exhibited an excellent regenerative ability, and is a promising sorbent for capturing Hg⁰