The oxidation of stepped Rh surfaces - a DFT study

Full text: Due to their relevance for catalytic reactions the investigation of Rh surfaces has been a major research field in surface science in the last years. Although most particles show no well-defined orientation under catalytic conditions, most studies have been restricted to low-indexed surface orientations. Stepped surfaces offer the means to investigate the catalytic properties approaching realistic conditions. Therefore the oxidation of a stepped Rh(553) surface has been studied using ab-initio local-density-functional calculations. The calculations were performed using the Vienna ab-initio simulation package (VASP) which is based on a plane wave basis set and PAW potentials. In the initial step the stable phases for the adsorption of O/Rh(553) at various oxygen coverages have been determined, thus allowing to establish a phase diagram. In the low-coverage limit the oxygen adsorption is dominated by the influence of the step, while for higher coverages a (10x1) reconstruction and finally the formation of a surface oxide are predicted. Yet, experimentally a reconstruction of stepped Rh surfaces has been observed for several surface orientations. Therefore the stability of the oxygen-covered Rh(553) surface versus faceting and step-bunching has been investigated in the second part of the study. In agreement with experimental data a driving force for the reconstruction of the surface towards Rh(331) and Rh(111) facets has been found for certain values of the chemical potential. A detailed explanation of the mechanisms of this driving force will be presented. (author)