Paper HC-ThP6
Comparative Reactivity of Oxide and Metallic Phases on Rh(111)

Thursday, October 25, 2018, 6:00 pm, Room Hall B

Recently, the understanding of the role of surface oxides in catalytic activity has changed. Instead of being thought of as poisons, similar to bulk oxides, they are now believed to be effective promoters of selective catalysis. We have chosen to study oxidation on Rh(111) as a model system; Rh effectively promotes oxidation reactions and is a benchmark system for models of heterogeneously catalyzed chemistry. Using atomic oxygen (AO) as an oxidizing agent, high coverage oxygen adlayers and oxides can be formed under ultra-high vacuum (UHV) conditions. Careful control of the AO exposure parameters allowed for the selective growth of the RhO₂surface oxide, surface adsorbed oxygen, and subsurface oxygen. Furthermore, formation of the RhO₂surface oxide was shown to rely not only on the presence of defects, as evident by the selective growth along step edges (Figure 1), but also on high concentrations of oxygen absorbed below the surface of the metal.

Utilizing our surface preparation techniques to carefully prepare specific oxidized Rh(111) surfaces, we use carbon monoxide (CO) as a probe molecule to track surface structure specific reactivity via CO oxidation. Exposing RhO₂to CO, TPD and STM are employed to gather information on CO₂production, residual O₂population, and surface structure evolution during CO oxidation reactions. In order to determine the actual reaction mechanism of CO oxidation on oxidized Rh(111), STM is needed to provide atomic scale resolution of the active surface adsorbates during the reaction progression, as shown in Figure 1. By combining spatially resolved structural information with CO₂production and oxygen consumption, we will be able to identify which oxidic species and surface sites contribute to CO oxidation. This information will help in determining the exact reaction mechanism occurring during CO oxidation over an oxidized Rh surface.