Density functional theory studies on ortho-position adsorption of SO3 at step sites of a CaO surface with SO2 and CO2.

[Display omitted] • Steps with O and Ca at the edges are the best termination for SO 3 adsorption. • Adsorption energy has a remarkable increase at edge sites on step surface. • Coordination of O and Ca at edges affect SO 3 adsorption. • Pre-adsorption of SO 3 or SO 2 at neighboring sites increases SO 3 adsorption energy. • SO 3 adsorption is more stable than the adsorption of SO 2 and CO 2 at edge sites. With the application of high-sulfur coal and oxy-fuel combustion in power plants, the formation of SO 3 in flue gas has strongly enhanced. Hence, the removal of SO 3 has received growing attention. Within this context, SO 3 sorption using calcium-based sorbents is an interesting approach. In this study, we analyzed the steps on a CaO surface and examined their influence on the adsorption of SO 3 molecules using density function theory calculations. The results indicate that steps with O and Ca atoms at the edges are the most stable terminations and also the best terminations for SO 3 adsorption. SO 3 molecules bind to O CaO sites by S SO3 atoms and weak bonds between Ca and O SO3 are formed. At edge sites, the adsorption energy of SO 3 , SO 2 and CO 2 shows a remarkable increase compared to that on a flat surface, whereas it decreases at the top site nearby the edge. The adsorption energy of SO 3 is also affected by the O CaO that interacts with S SO3 and the Ca near the O CaO. Interestingly, the SO 3 adsorption energy can increase if an SO 3 , SO 2 or CO 2 molecule previously adsorbed at a neighboring site. SO 3 adsorption is more stable than SO 2 and CO 2 absorption on step surface and has an advantage in competitive adsorption with SO 2 or CO 2. The calculation results thus indicate that the formation of a step surface could be an effective method to enhance SO 3 sorption on calcium-based sorbents. [ABSTRACT FROM AUTHOR]