DFT study of Se and SeO2 adsorbed on CaO (001) surface: Role of oxygen

The effect of pre-adsorbed O-2 on selenium removal by CaO was investigated by density functional theory (DFT) calculations. Adsorption configurations of Se and SeO2 on CaO (0 0 1) surface with pre-adsorbed O-2 were optimized. And the conversion of Se to SeO2 on CaO (0 0 1) surface has been studied as well. Results showed that O-2/CaO (0 0 1) surface had weaker adsorption ability than CaO (0 0 1) surface for both Se and SeO2, which indicated that pre-adsorbed O-2 was not beneficial to selenium capture. When Se atom adsorbed on O-2/CaO (0 0 1) surface, two kinds of stable adsorption configurations were formed: O-Se-O group and O-O-Se group on CaO (0 0 1) surface with chemical activities. When SeO2 molecule adsorbed on O-2/CaO (0 0 1) surface, some valence electrons in adsorption substrate transferred into the orbits of SeO2 molecule, forming Se-O covalent bond. Additionally, the reaction energy barrier of Se and O-2 conversing into SeO2 in heterogeneous was less than that in homogeneous, which indicated that CaO could not only act as an adsorbent, but also promote the conversion of Se to SeO2.