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

Identifying the rate-controlling steps and the evolution of the ligand environment throughout the catalytic cycle on supported single-atom catalysts is crucial to bridge the gap between heterogeneous and homogeneous catalysis. Here we identified the rate-controlling elementary steps for CO oxidation on TiO2-supported Ir single atoms and isolated the corresponding intermediate Ir complexes. Kinetic measurements, operando spectroscopy, and quantum-chemical calculations indicate that the reaction mechanism has two kinetically relevant steps, CO adsorption/oxidation and O2 dissociation. By varying the reaction conditions, three Ir1 complexes (states) along the reaction cycle were isolated and identified using in situ spectroscopy. Furthermore, we show that all the intermediate Ir1 states share a common CO ligand that does not turn over. This study provides atomic level details on the active, intermediate complexes and reaction cycle of supported single-metal-atom catalysts, thereby offering future possibilities to control the ligand environment and reactivity.