Identification of Surface Sites for Low-Temperature Heterogeneously Catalyzed CO Oxidation on Rh(111)

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.