On the mechanism of reactive sorption of H ₂ S on CuO (111) and (111) 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 (<i>e.g.</i>, 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.