The effect of SO₂ on CaO capture selenium in the flue gas: Density functional theory and experimental study

In this work, the mechanism of SO2 on CaO capture selenium was deeply investigated combined density functional theory (DFT) with adsorption experiments. The fixed-bed experiments result showed that SO2 inhibited CaO capture selenium from 0 to 1000 while promoted in the range of 1000-2000 ppm, and CaSeO3 was the primary adsorption product at 850 C. Freundlich equation accurately predicted the adsorption capacity of CaSO4 for SeO2 with the concentration from 0 to 800 ppm, indicating weak adsorption activities for SeO2. Furthermore, the SO2 and selenium oxides adsorption mechanism was studied by DFT. It demonstrated that SO2 and SeO2 were adsorbed on CaO (001) surface involved chemical adsorption with oxygen atoms as adsorption sites, which led to the competition of SO2 and SeO2 for adsorption sites on the CaO surface. SO2 adsorbed on the CaO surface inhibited the activity of neighboring adsorption sites for SeO2. Moreover, compared with SeO2, SeO and Se-0 reduced by SO2 were more beneficial adsorbed by CaO, the conversion of SeO2 to selenium and SeO was firstly proposed in selenium adsorption. In detail, SO2 promoted CaO capture selenium through homogeneous selenium conversion. Finally, it was identified that the CaSO4 (001) surface was inert for selenium adsorption in the flue gas, indicating CaO transition to CaSO4 inhibited selenium adsorption.