Effect of H2S orientation on its dissociation on Fe(110) surface*

Over the years, there has been  interest in the design of efficient system that inhibits corrosion on metallic surfaces. This is because the deterioration of the metals, so-called metal dusting incurs great cost to the economy. This process involves the transfer of carbon into solid solution saturating the metal phase in the process. When this occurs, cementite forms at the surface and serves as barrier to the diffusion of the carbon into the metal surface. One way proposed to tackle this is the addition of Sulfur-based compound, for instance H2S to the environment where these reactions take place.The presence of H2S in this environment allows the adsorption of sulfur on the Fe surface.This leads to the retardation of the transfer of C as the adsorbed sulfur blocks the reaction sites. In order to effectively utilize this approach, it is important to understand the kinetics of the retarding procedure.We present density functional theory calculations on the role of orientation of H2S molecule on its adsorption and dissociation on Fe (110) surface.Our investigation considered different concentration of H2S: high (0.25ML) and low (0.0625ML)  respectively. We report the geometries and energetics for an exhaustive set of adsorption and decomposition states induced by H2S molecule on the considered coverages. We find that H2S can be either adsorbed as a molecule or as HS+H depending on the orientation of the molecule and the site of adsorption. Molecular H2S was found to adsorb weakly on either the long or short bridge sites which are potential reaction sites for the carburization.Our findings show that the orientation of H2S play significant role in determining the elementary pathways to its dissociation on Fe (110) surface.