Elucidation of the Active Sites in Single-Atom Pd1/CeO2 Catalysts for Low-Temperature CO Oxidation

Supported precious metals with atomic dispersion are of great interest in catalysis due to their potentials in achieving maximum atom efficiency and unique reactivities. Herein, the active sites for low-temperature CO oxidation are elucidated over single-atom Pd1/CeO2 catalysts prepared via high-temperature atom trapping (AT). The increased oxygen vacancies on CeO2 surface induced by 800 °C air calcination result in decreased Pd–CeO2 coordinations, i.e., the coordination-unsaturated Pd2+ on CeO2. Light-off and light-out measurements coupled with CO-DRIFTS and X-ray absorption characterization confirm that these coordination-unsaturated Pd2+ on CeO2 are much more reactive than the fully coordinated counterpart, evidenced by a decrease of T 90 (temperature to achieve 90% conversion) by ∼100 °C in CO oxidation at a gas hourly space velocity of 300 L g–1 h–1.