A mechanistic study of H_2S adsorption and dissociation on Cu_2O(111) surfaces: Thermochemistry, reaction barrier

摘要

The interaction mechanism of H_2S with different Cu_2O( 111) surfaces, including perfect, oxygen-vacancy and sulfur-containing surfaces, have been systematically studied using periodic density functional cal culations. Different kinds of possible modes of H_2S, as well as the resultant SH and S species adsorbed on these surfaces are identified. Two types of pathways via molecular and dissociative adsorption processes are mapped out. Our results show that sulfur species (H_2S, SH and S) interact with surface Cu centers; H_2S exists in the form of molecular adsorption on perfect and sulfur-containing surfaces; the dissociative adsorption of H_2S occurs predominantly on oxygen-vacancy surface, suggesting that oxygen-vacancy exhibits a strong catalytic activity toward the dissociation of H_2S. On the other hand, the dissociation processes of the molecular and dissociative adsorption H_2S, leading to final product S species on these Cu_2O(1 11) surfaces, show that the overall dissociation process is exothermic. Meanwhile, with respect to molecular adsorption H_2S, the activation barrier and reaction energy of the overall dissociation process on perfect and oxygen-vacancy surfaces indicate that H_2S can easily dissociate into S species. Impor tantly, in the case of dissociative adsorption of H_2S, the dissociation of H_2S into S species is a spontaneous process with respect to molecular adsorption H_2S. However, on sulfur-containing surface, the presence of surface S atom goes against the H-S bond-breaking process both thermodynamically and kinetically. Finally, the vibrational frequencies for the adsorbed H_2S, SH and S species on these surfaces have been obtained, which can be applied to guide surface vibrational spectroscopy in experiment.