Supported single atoms provide an opportunity to design new heterogeneous catalysts while optimizing the utilization of noble metals. However, identification of the active single-atom structure is required for understanding the reaction mechanism and guiding catalyst design. Here, we use in situ infrared spectroscopy, operando X-ray absorption spectroscopy and quantum chemical calculations to identify the active single-atom complex as well as the resting state of the Ir/MgAl2O4 catalysts during the low-temperature CO oxidation. In contrast to poisoning of iridium nanoparticles by CO, here we show that 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 Ir(CO) provides an interfacial site for facile O2 activation between Ir and Al and lowers the reaction barrier between gas-phase CO(g) and *O in Ir(CO)(O) through an Eley–Rideal mechanism.
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This research was primarily sponsored by the Army Research Office and was accomplished under grant number W911NF-16-1-0400. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Office or the US Government. The US Government holds copyright license rights specified under the aforementioned grant. Additional support by SABIC (Saudi Basic Industries Corporation) and by the US Department of Energy (DOE) Office of Basic Energy Sciences to the SUNCAT Center for Interface Science and Catalysis is acknowledged. Use of the Stanford Synchrotron Radiation Light Source (SSRL, beamlines 6-2, user proposal 4645), SLAC National Accelerator Laboratory is supported by the US Department of Energy, Office of Basic Energy Sciences under contract no. DE-AC02-76SF00515. STEM imaging was performed at the William R. Wiley Environmental Molecular Science Laboratory (EMSL) sponsored by the US Department of Energy, Office of Biological and Environmental Research located at Pacific Northwest National Laboratory (PNNL) under science theme proposal 49326. Computing time was awarded at EMSL under the same proposal. L.Y. and H.X. acknowledge the partial financial support from the American Chemical Society Petroleum Research Fund (ACS PRF 55581-DNI5) and computational support from the Advanced Research Computing group at Virginia Polytechnic Institute and State University.