Enhancing the reactivity of clean, defect-free epitaxial graphene by the substrate-Experiment and theory

Experimental and theoretical evidence is presented that a sulfur compound dissociates on clean, defect-free epitaxial graphene (Gr) in ultrahigh vacuum (UHV). Together with density functional theory calculations (DFT), experimental kinetics and spectroscopic data suggest an auto-(/self)catalytic process. The results could open a pathway to a carbocatalyst. While adsorbing H2S in UHV at low temperatures on single-layer graphene/ruthenium (Gr/Ru), H-2 desorbs and sulfur remains on the surface. Vacancy and grain boundary defects, respectively, can be excluded as active sites. DFT results indicate the importance of the Ru(0001) support in facilitating a reaction pathway with small activation energy for H2S dissociation. Gr becomes reactive due to a complex interplay of structural and electronic effects, including the corrugation of the graphene layer and the hybridization of ruthenium's d orbital with antibonding states of H2S.