Enhancing the oxidation efficiency of elemental mercury in the presence of NO and SO2 by using Cu(II)O doped TiO2 photothermal catalysts: Kinetics and mechanisms

Abstract

This study aimed to apply sol–gel synthesized Cu(II)O doped TiO2 to enhance the oxidation of gaseous elemental mercury (Hg0) in the flue gases containing NO and SO2 at the temperatures of 120-180℃ under the irradiation of near-ultraviolet (near-UV). The influences of SO2 and NO on the oxidation efficiency of Hg0 were investigated by in-situ diffuse reflection infrared spectroscopy (DRIFT) and density functional theory (DFT). Experimental results showed that an optimal 5 %Cu(II)O/TiO2 had the oxidation efficiencies of Hg0 from 40 to 100 % at 120-180℃. The oxidation efficiencies of Hg0 were 85 and 70 % at 120℃, and 40 and 5 % at 180 °C, in the presence of solely SO2 and NO, respectively. Surface characterization showed that Cu(II)O was evenly dispersed over the surface of TiO2 catalysts. NO could inhibit the oxidation of Hg0 since it consumed the chemisorbed oxygen (Oα) and compete with Hg0 at the surface active sites. In contrast, SO2 could promote the oxidation efficiency of Hg0 due to the formation of HgSO4 on the surface of Cu(II)O/TiO2 catalysts. In the exposure of NO/SO2, NO and SO2 can be adsorbed on the catalyst surface reacting with ̇OH. The photothermal oxidation reactivity of Hg0 was inhibited due to the competitive adsorption between NO/SO2 and Hg0. The Langmuir-Hinshelwood (L-H) kinetic model successfully simulated the oxidation rate of Hg0. Moreover, DFT was further applied to estimate the binding energies of different gas molecules confirming the competence for active sites on the surface of Cu(II)O/TiO2 between NO/SO2 and Hg0.