Investigation on synergistic oxidation behavior of NO and Hg0 during the newly designed fast SCR process

Abstract

In the present study, elemental mercury (Hg0) oxidation behavior in the NO oxidation step of fast SCR process was investigated. The Mn doped CeO2-ZrO2 (CZM0.3) was selected as the catalyst, due to its superior oxygen storage capacity. The results showed that NO could be oxidized efficiently over the catalyst at around 250 °C under the atmosphere of NO/O2/N2. In the Hg0/NO/O2/N2 reaction system, NO oxidation reaction remarkably improved Hg0 oxidation efficiency. Two domination reaction pathways were proposed to interpret the influence of NO oxidation reaction on Hg0 oxidation: one through a heterogeneous oxidation process, and the other through a homogeneous reaction. In the heterogeneous oxidation process, NO was adsorbed on the active sites and activated by the surface oxygen to form more active intermediates for Hg0 oxidation. Hg0 was probably oxidized in its gaseous state, since the affinity between NO and the catalyst was stronger than that between Hg0 and the catalyst. The other reaction pathway was a homogeneous route, during which the gaseous NO2 generated by NO oxidation could oxidize the gaseous Hg0 within the designed reaction conditions. According to the present research, synergistic oxidation of NO and Hg0 in the first step of fast SCR appears to be a promising way to remove Hg0 and NOx in coal-fired power plants.