In situstructural imaging of CO oxidation catalysis on oxidized Rh(111)

Metallic rhodium is an active catalyst for CO oxidation while the bulk Rh₂O₃ oxide is inactive, but the detailed relation between oxidation stage and reactivity is not clear at present. Here, we study CO oxidation on oxidized Rh(111) surfaces using in situ intensity-voltage low-energy electron microscopy. By following the structural changes during the reaction we identify the range of catalytically active surface phases between the (2×2)-O structure and the O-Rh-O trilayer corresponding to oxygen coverages between 0.25 and 2.0 ML. Further surface oxidation results in the formation of a double trilayer structure, which induces the deactivation of the catalyst.