Insights into selenium capture by Fe-modified MgO: Experimental and density functional theory study

Abstract

Fe-doped MgO sorbents were developed for gaseous selenium removal in the flue gas. Combined with the density functional theory (DFT), the molecular interaction was described. The experimental results showed that the synthesis of MgFe2O4 increased the number of lattice oxygen in the adsorbent. Moreover, the oxygen vacancy played as a pit in the filling of O atoms in SeO2. There were two desorption peaks of SeO2 on the surface of Fe-loaded MgO, 420 °C and 540 °C, respectively. Fe0.02MgO and Fe0.05MgO exhibited the best selenium capture capacity at 500 °C, which depended on the SeO2 desorption temperature of 540 °C. Fe0.1MgO had advantages in capturing selenium at 400 and 700 °C. DFT results indicated that the exposed Fe atoms on the surface of MgFe2O4 provided abundant adsorption sites for selenium. The adsorption energy of SeO2 on MgFe2O4 was 2.4 times that of pure MgO. SeO2 decomposed on MgFe2O4 surface to form Se0 with a conversion energy barrier of 52.4 kJ/mol. Thermodynamic calculations showed that the selenium capture capacity of MgFe2O4 gradually decreased with the increase of temperature, while the conversion of selenium on the MgFe2O4 surface was promoted.