First-Principles Study on O2 Adsorption and Dissociation Processes over Rh(100) and Rh(111) Surfaces.

Through DFT calculations, a systematic description of O2 adsorption and dissociation processes over Rh(100) and Rh(111) surfaces has been provided. The dominance of parallel orientation in molecularly adsorbed states and during the impinging processes has been identified, along with the explicit adsorption configurations and preferred impinging trajectories on both surfaces. The dissociation of O2 is found to occur either by precursor-mediated adsorption or by direct dissociation. O2 in its initial precursor state dissociates facilely on Rh(100), but this is a little harder on Rh(111) by going through a two-step process. The latter can be described as a preliminary rotation and subsequent dissociation, with the final locations of two O atoms disturbed easily by coadsorbed O atoms surrounding the dissociating O2 molecule due to the existence of a relatively flat potential energy surface stage along the way. The present work may provide the basis for kinetic modeling to investigate the catalytic properties on a realistic scale.