Enhanced oxidation on stepped Rh surfaces

Understanding how surface structure influences oxidation processes is essential for advancing the design of metal-based catalysts. In this study, we investigated how oxygen adsorbed on a bifaceted Rh(111)/(322) single crystal using low-energy electron diffraction (LEED) and temperature programmed desorption (TPD). The (111) facet represented a flat, close-packed surface, while the (322) facet introduced a high density of well-defined, repeating stepped features with more undercoordinated atoms. Our results revealed pronounced structure sensitivity. Low temperature atomic oxygen exposures lead to enhanced O coverages on both facets; however, LEED revealed an ordered overlayer on Rh(111) and a faintless crystalline adlayer on Rh(322). Oxygen exposures at 600 K caused oxide formation on the (111) facet but not on the (322) facet, and oxide was not observed on either facet for lower temperature O2 exposures. Notably, the additional O uptake was observed. While TPD measurements show similar adsorption energies for the various oxygen species, LEED analysis reveals clear structural differences on the stepped surface. These findings highlight the critical role of facet-specific coordination environments in dictating oxidation behavior and having insight into oxygen mobility across catalytic surfaces.