Formation of metastable, heterolytic H-pairs on the RuO2(110) surface

The interaction of molecular hydrogen (H2) with the stoichiometric RuO2(110) surface was studied at various temperatures and coverages by high-resolution scanning tunneling microscopy (STM) and temperature-programmed reaction (TPR). Metastable, heterolytic H-pairs of dissociated H2 consisting of one H adsorbed on a surface Ru atom and the other H at an adjacent bridging O atom are identified. This H-pair configuration is consistent with accompanying density functional theory (DFT) calculations and spectroscopic data. We propose that such metastable, heterolytic H-pairs are a typical feature of late transition metal oxide surfaces. Furthermore, the adsorption temperature was found to be decisive for the configuration of the adsorbed hydrogen species and the sticking of H2.