SeO₂ adsorption on CaO surface: DFT study on the adsorption of a single SeO₂ molecule

Selenium is a hazardous element in coal. During coal combustion, most of the selenium will convert to SeO₂ in the flue gas. Ca-based adsorbents, especially CaO, have been considered as a potential sorbent to adsorb SeO₂ due to its low cost. In this paper, the adsorption mechanisms of single SeO₂ on CaO surface were investigated by density functional theory (DFT) calculation. Both the physisorption and chemisorption structures were determined. It has been identified that the adsorption of SeO₂ on CaO surface is primarily chemisorption, while physisorption takes effects at the initial stage of the process. Under O₂ atmosphere, selenate is hard to form. Most of the adsorption products are selenite. Additionally, the electron density maps were obtained to reveal the surface active sites. The partial density of states (PDOS) was calculated for analyzing the electronic structural change of SeO₂ and CaO surface during adsorption. The results provide fundamental information of the adsorption process, which could be meaningful for the development of new absorbents.