CO Oxidation on Ir₁/TiO₂: Resolving Ligand Dynamics and Elementary Reaction Steps

Identifying the rate-controlling steps and the evolutionof theligand environment throughout the catalytic cycle on supported single-atomcatalysts is crucial to bridge the gap between heterogeneous and homogeneouscatalysis. Here we identified the rate-controlling elementary stepsfor CO oxidation on TiO2-supported Ir single atoms andisolated the corresponding intermediate Ir complexes. Kinetic measurements,operando spectroscopy, and quantum-chemical calculations indicatethat the reaction mechanism has two kinetically relevant steps, COadsorption/oxidation and O-2 dissociation. By varying thereaction conditions, three Ir-1 complexes (states) alongthe reaction cycle were isolated and identified using in situ spectroscopy.Furthermore, we show that all the intermediate Ir-1 statesshare a common CO ligand that does not turn over. This study providesatomic level details on the active, intermediate complexes and reactioncycle of supported single-metal-atom catalysts, thereby offering futurepossibilities to control the ligand environment and reactivity.