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We combine velocity map imaging (VMI) with temperature-programmed desorption (TPD) experiments to record the angular-resolved velocity distributions of recombinatively-desorbing oxygen from Rh(111). We assign the velocity distributions to desorption from specific surface and sub-surface states by matching the recorded distributions to the desorption temperature. These results provide insight into the recombinative desorption mechanisms and the availability of oxygen for surface-catalyzed reactions.
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Heterogeneously catalyzed reactions over transition metal surfaces are pillars of chemical industry and account for a significant fraction of the global energy demand. CO oxidation provides insight into the relative reactivity of various oxygenaceous surface phases, and it is necessary to first understand where it binds to the surface and the nature of the local environment to develop robust mechanistic pictures of the reaction. Surface IR spectroscopy is a quantitative technique that also provides information about the binding sites and chemical environments of the adsorbed CO molecules. Here, we report results from a study of CO sticking to clean Rh(111) and (2 × 1)-O/Rh(111) that shows that the intensity of the IR absorption was not linear with coverage and is an important consideration for further studies of the catalytic surface.more » « less
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In heterogeneously catalyzed oxidation reactions on metal surfaces, advantageous oxygenaceous species proffer lower barrier reaction pathways. In order to utilize such reactions better, it is essential to understand what species are present, how they are formed, and under what conditions they are available for reaction. Oxides, adsorbed oxygen, and subsurface oxygen each form on Rh(111) surfaces and thus provide the opportunity to distinguish the contributions of each species to the overall reactivity. In an effort to elucidate relevant reaction sites on catalytically active rhodium surfaces, a combination of scanning tunneling microscopy (STM) and temperature-programmed desorption (TPD) showed that when subsurface oxygen is present, CO was readily oxidized at the interface between the metallic and oxidic phases at relatively modest temperatures.more » « less
