Ultrasmall Pd Clusters in FER Zeolite Alleviate CO Poisoning for Effective Low-Temperature Carbon Monoxide Oxidation

Ultrasmall Pd₄ clusters form in the micropores of FER zeolite during low-temperature treatment (100 °C) in the presence of humid CO gas. They effectively catalyze CO oxidation below 100 °C, whereas Pd nanoparticles are not active as they are poisoned by CO. Using catalytic measurements, infrared (IR) spectroscopy, X-ray absorption spectroscopy (EXAFS), microscopy, and density functional theory calculations, we provide the molecular-level insight into this previously unreported phenomenon. Pd nanoparticles get covered with CO at low temperatures, which effectively blocks O₂ activation until CO desorption occurs. Small Pd clusters in zeolites, in contrast, demonstrate fluxional behavior in the presence of CO, which significantly increases the affinity for binding O₂. Our study provides a pathway to achieve low-temperature CO oxidation activity on the basis of a well-defined Pd/zeolite system.