PNNL

Abstract

Supported single atoms provide the best utilization of noble metals and provide an opportunity to design new heterogeneous catalysts. However, identification of the active single atoms structure is required for understanding the reaction mechanism and guiding catalyst design. We used in-situ infrared spectroscopy, in-operando x-ray adsorption spectroscopy and quantum chemical calculations to show that Ir(CO)/MgAl2O4 is the active single atom complex for low temperature CO oxidation and Ir(CO)(O) is the most stable intermediate. In contrast to poisoning of nanoparticles by CO, the formation of Ir(CO) on single atoms results in a different reaction mechanism and high activity for low temperature CO oxidation. This is due to the ability of single atoms to coordinate with multiple ligands, where CO, in Ir(CO)(O), acts as a facilitator by lowering the reaction barrier between gas phase CO and adsorbed O (Eley-Rideal mechanism).