The structure of RuO2(110) and the mechanism for catalytic carbon monoxide oxidation on this surface were studied by Low-energy electron diffraction, scanning tunneling microscopy, and density-functional calculations. The RuO2(110) surface exposes bridging oxygen atoms and ruthenium atoms not capped by oxygen, The Latter act as coordinatively unsaturated sites-a hypothesis introduced Long ago to account for the catalytic activity of oxide surfaces-onto which carbon monoxide can chemisorb and from where it can react with neighboring Lattice-oxygen to carbon dioxide, Under steady-state conditions, the consumed Lattice-oxygen is continuously restored by oxygen uptake from the gas phase. The results provide atomic-scale verification of a general mechanism originally proposed by Mars and van Krevelen in 1954 and are likely to be of general relevance for the mechanism of catalytic reactions at oxide surfaces.
