First-principles study of the adsorption and reaction of Se and SeO₂ on O₂/CaO(001) surface

O₂/CaO(001) surface with the lowest energy was built by using the slab model and the first-principles method based on density functional theory. A series of possible adsorption configurations were optimized to get the adsorption geometries with the lowest energy for selenium (Se) and SeO₂ on the O₂/CaO(001) surface and the conversion of Se to SeO₂ on the CaO(001) surface was then investigated. The results indicate that there are two adsorption configurations for Se atom on the O₂/CaO(001) surface, viz., O-Se-O and O-O-Se groups; therein the Se terminal in O-O-Se group has a certain chemical activity. The reaction energy barrier for the heterogeneous conversion of Se and O₂ to SeO₂ is less than that for the homogeneous conversion, which means that CaO can not only act as an adsorbent, but also promote the conversion of Se to SeO₂ as a catalyst; certain valence electrons in adsorption substrate are transferred to the orbits of SeO₂ molecule when SeO₂ molecule was adsorbed on the O₂/CaO(001) surface.