The effect of step-edges on the dissociative adsorption of H2S has been studied on a Ni(111) surface using scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). Exposure of Ni(111) to H2S at room temperature results in the formation of S islands with the structures of p(2×2) and reconstructed c(5√3×9) rect in the vicinity of step-edges. Subsequently, H2S dissociates on the terrace of Ni(111), leading to the formation of unique S species with a string structure. The STM observation indicates that the dissociation of H2S takes place on both step-edges and terraces. The dissociative adsorption of CO as well as formation of carbide islands also take place preferentially at the step-edges. It is thus suggested that a small amount of sulfur located at step-edges effectively deactivate CO dissociation in the methanation reaction.
