ABSTRACT
Vacancy defects are inherent point defects in materials. In this study, we investigate the role of Fe vacancy (VFe) and S vacancy (VS) in the interaction (adsorption, dissociation, and diffusion) between H2S and the FeS(001) surface using the dispersion-corrected density functional theory (DFT-D2) method. VFe promotes the dissociation of H2S but slightly hinders the dissociation of HS. Compared with the perfect surface (2.08 and 1.15 eV), the dissociation energy barrier of H2S is reduced to 1.56 eV, and HS is increased to 1.25 eV. Meanwhile, S vacancy (VS) significantly facilitates the adsorption and dissociation of H2S, which not only reduces the dissociation energy barriers of H2S and HS to 0.07 and 0.11 eV, respectively, but also changes the dissociation process of H2S from an endothermic process to a spontaneous exothermic one. Furthermore, VFe can promote the hydrogen (H) diffusion process from the surface into the matrix and reduce the energy barrier of the rate-limiting step from 1.12 to 0.26 eV. But it is very hard for H atoms gathered around VS to diffuse into the matrix, especially the energy barrier of the rate-limiting step increases to 1.89 eV. Finally, we propose that VS on the FeS(001) surface is intensely difficult to form and exist in the actual environment through the calculation results.
ABSTRACT
In the actual environment, impurity atoms significantly affect the adsorption/dissociation of gas molecules on the substrate surface and in turn promote or impede the formation of subsequent products. In this study, we investigate the effects of three kinds of impurity atoms (H, O, and S) on the adsorption/dissociation of hydrogen sulfide (H2S) and hydrogen (H) diffusion processes by using the density functional theory method. We found that impurity atoms can change the charge density distribution of the surface and thus affect the adsorption/dissociation process of H2S. The existence of a H atom reduces the dissociation barrier of H2S. The adsorption site of H2S near the O atom is transferred from the bridge site to the adjacent top site and the first-order dissociation barrier of H2S is 0.07 eV, which is prominently lower than that of the pristine surface (0.28 eV). The presence of a S atom transfers the adsorption site of H2S to a farther bridge site and effectively affects the dissociation process of H2S. Both O and S atoms hinder the dissociation process of HS. Moreover, the diffusion process of H atoms to the subsurface can be slightly impeded by the O atom. Our work theoretically explains the influence mechanism of impurity atoms on the adsorption/dissociation of H2S and H diffusion behavior on the Fe(100) surface.
