Interaction of SO2 with MgO(100) and Cu/MgO(100): Decomposition Reactions and the Formation of SO3 and SO4

Abstract

Synchrotron-based high-resolution photoemission and first-principles density functional calculations (DFT-GGA) were used to study the interaction of SO2 with clean and modified (OH, Oδ-, O vacancies, or Cu adatoms present) MgO(100) surfaces. The reaction of the molecule with pure and hydroxylated powders of MgO was investigated using X-ray absorption near-edge spectroscopy (XANES). At 100 K, the main product of the adsorption of sulfur dioxide on MgO(100) is sulfite (SO2,gas + Olattice → SO3,ads). No evidence is found for bonding of SO2 to Mg sites of the surface or decomposition of the molecule. DFT calculations show that a η3-S,O,O adsorption configuration leads to a SO3-like species, and this is much more stable than configurations which involve bonding to only Mg sites or formation of SO4. On a flat MgO(100) substrate, the formation of SO4 is not energetically viable. A SO3 → SO4 transformation is observed at temperatures between 150 and 450 K with a substantial reconstruction of the oxide surface. Fr...