Gaseous selenium removal by metal oxide sorbent: Experimental and density functional theory study

Abstract

The characteristic of metal oxides capture SeO2 was investigated, and the adsorption sites, adsorption energy, and surface transformation were clarified via density functional theory (DFT). The adsorption experiments confirmed the adsorption sequence followed: fine particle Al2O3 > MgO > CaO > Fe2O3, where CaSeO3, MgSeO3, Al2(SeO3)3 and Se2-/Se0/Se4+/Fe as the adsorption product. Based on the instability of adsorption products, the adsorption effect of CaO and MgO became better within the range of 400–550 °C, while the adsorption capacity of Fe2O3 and Al2O3 decreased if exceeding 400 °C. Due to the effect of CO2 in the flue gas and the dense pore structure, the retention of SeO2 on CaO surface was inhibited. From the XPS results, Se2- was the stable selenium species on Fe2O3 surface at high temperature. Furthermore, according to the density functional theory calculation, all metal oxides captured SeO2 involved chemical adsorption, where the adsorption sites correspond to the adsorbents: O top sites (CaO and MgO), Al and O top sites (Al2O3), and Fe top sites (Fe2O3). Finally, it was identified Fe top sites were the active adsorption sites for Se0, and the transformation of selenium on Fe2O3 surface was also intensively explored as a three-step process: SeO2 adsorption, Se4+→Se0, and Se0 → Se2-.