Adsorption of SO2 on Li atoms deposited on MgO (1 0 0) surface: DFT calculations

The adsorption of sulfur dioxide molecule (SO2) on Li atom deposited on the surfaces of metal oxide MgO (1 0 0) on both anionic and defect (Fs-center) sites located on various geometrical defects (terrace, edge and corner) has been studied using density functional theory (DFT) in combination with embedded cluster model. The adsorption energy (Eads) of SO2 molecule (S-atom down as well as O-atom down) in different positions on both of O−2 and Fs sites is considered. The spin density (SD) distribution due to the presence of Li atom is discussed. The geometrical optimizations have been done for the additive materials and MgO substrate surfaces (terrace, edge and corner). The oxygen vacancy formation energies have been evaluated for MgO substrate surfaces. The ionization potential (IP) for defect free and defect containing of the MgO surfaces has been calculated. The adsorption properties of SO2 are analyzed in terms of the Eads, the electron donation (basicity), the elongation of S-O bond length and the atomic charges on adsorbed materials. The presence of the Li atom increases the catalytic effect of the anionic O−2 site of MgO substrate surfaces (converted from physisorption to chemisorption). On the other hand, the presence of the Li atom decreases the catalytic effect of the Fs-site of MgO substrate surfaces. Generally, the SO2 molecule is strongly adsorbed (chemisorption) on the MgO substrate surfaces containing Fs-center.

Research highlights► The SO2 molecule in both cases (S-atom down) or (O-atom down) preferably adsorbed on MgO(Fs) than on regular MgO(O−2) sites for the MgO substrate surfaces. ► The strong adsorption (chemisorption) of SO2 molecule on Fs site may be referred to the high basicity of the MgO substrate surfaces containing Fs. ► The Fs-site substrate surfaces lead to form a stable surface sulfite. ► The SO2 molecule is strongly adsorbed when O-atom down toward Li/MgO(O−2) systems than S-atom down toward Li/MgO(O−2) systems. ► The Li atom supported by MgO(O−2) substrate surfaces convert the adsorption processes of SO2 on Li/MgO(O−2) systems from physisorption into chemisorption, therefore, the Li atom supported by MgO(O−2) substrate surfaces have a catalytic activity. ► The spin density (SD) distributions between Li atom and SO2 molecules in the SO2/Li/MgO(O−2) systems play a rule for the change of the adsorption processes from physisorption into chemisorption.