On the mechanism of reactive sorption of H₂S on CuO (111) and (1̄11) surfaces: a first-principles study

Hydrogen sulfide (H₂S) is a toxic and corrosive impurity present in industrial gas streams. An effective method for H₂S removal is through reactive sorption with metal oxides. This work investigates the reaction of H₂S on CuO surfaces to produce water and CuS. Using density functional theory (DFT), the elementary steps involved in H₂S adsorption and dissociation on the CuO (111) and (1̄11) surfaces are modelled. The three-coordinated oxygen atoms (O₃c) on CuO surfaces are highly reactive and facilitate H₂S dissociation at room temperature, whereas four-coordinated oxygen atoms (O₄c) are less reactive, requiring higher temperatures for effective H₂S dissociation. Partial sulfidation of the surface, however, stabilizes the substitution of O₄c by sulfur, making the dissociation of H₂S thermodynamically favorable but kinetically demanding at room temperature. Proton transfer steps, such as water formation, are generally favorable, while heavier atom migrations (e.g., hydroxyl migration and vacancy healing) are energetically costly. Near ambient temperature conditions promote the replacement of all O₃ and O₄ atoms at the surface, facilitating further sulfidation and H₂S adsorption. This computational understanding of the reaction mechanism provides insights into the reactive behavior of CuO surfaces in the purification of H₂S.