DFT Study of SO ₂ Binding on Cu ₂ O during Chemical Looping with Oxygen Uncoupling: Effects of Flue Gas Components and Surface Oxygen Vacancy

In this study, binding of SO2 on the Cu2O(111) surface was investigated by employing DFT and ab initio thermodynamics to explore the possible interactions of SO2 with copper-based oxygen carriers in the chemical looping with oxygen uncoupling (CLOU) process. SO2 forms a sulfite-like species on the Cu2O(111) surface. The presence of the flue gas components, H2O and CO2, and SO2 adsorbed on the surface lowers the SO2 binding energy compared to that on the clean surface. In the presence of an oxygen vacancy, the SO2 molecule binds to the Cu2O(111) surface by occupying the vacant site with one of its oxygen atoms with a higher binding energy compared to the surface without any vacancy, indicating a positive effect of the oxygen vacancy on SO2 binding. Finally, ab initio thermodynamics calculations indicate that SO2 on the Cu2O(111) surface is thermodynamically unstable within the CLOU operating temperature range of 800–1000 °C.