Identification of Intermediates in the Reaction Pathway of SO2 on the CaO Surface: From Physisorption to Sulfite to Sulfate

Nils Schewe; Farahnaz Maleki; Giovanni Di Liberto; Andreas Gerdes; Hicham Idriss; Gianfranco Pacchioni; Christof Wöll

doi:10.1002/chem.202203956

Identification of Intermediates in the Reaction Pathway of SO₂ on the CaO Surface: From Physisorption to Sulfite to Sulfate

Chemistry. 2023 Apr 21;29(23):e202203956. doi: 10.1002/chem.202203956. Epub 2023 Mar 16.

Authors

Nils Schewe¹, Farahnaz Maleki², Giovanni Di Liberto², Andreas Gerdes¹, Hicham Idriss¹, Gianfranco Pacchioni², Christof Wöll¹

Affiliations

¹ Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), 76344, Eggenstein-Leopoldshafen, Germany.
² Department of Materials Science, University of Milano-Bicocca, 20125, Milano, Italy.

PMID: 36645202
DOI: 10.1002/chem.202203956

Abstract

The interaction of CaO and Ca(OH)₂ with solvated or gaseous SO₂ plays a crucial role in the corrosion of urban infrastructure by acid rain or in the removal of SO₂ from flue gas. We carried out a combined spectroscopic and theoretical investigation on the interaction of SO₂ with a CaO(001) single crystal. First, the surface chemistry of SO₂ was investigated at different temperatures using polarization-resolved IR reflection absorption spectroscopy. Three species were identified, and an in-depth density functional theory study was carried out, which allowed deriving a consistent picture. Unexpectedly, low temperature exposure to SO₂ solely yields a physisorbed species. Only above 100 K, the transformation of this weakly bound adsorbate first to a chemisorbed sulfite and then to a sulfate occurs, effectively passivatating the surface. Our results provide the basis for more efficient strategies in corrosion protection of urban infrastructure and in lime-based desulfurization of flue gas.

Keywords: Acid rain; CaO(001); IRRAS; SO2.