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

Metallic rhodium is an active catalyst for CO oxidation while the bulk Rh(2)O(3) 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 (2x2)-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.