Dynamic Intermediate Coordination on Cerium Dual Sites in MOFs Boosts Selective Epoxidation of Alkenes

ABSTRACT CeO 2 is widely studied in catalysis but struggles with precise defect and microenvironment modulation. Here, we report modulating dynamic coordination and microenvironment of defective Ce pairs on Ce 6 ‐oxo clusters in cerium terephthalate UiO‐66 for selective oxidation. With one coordinative vacancy per Ce site in dual‐site pairs, cerium 2‐fluoroterephthalate UiO‐66 exhibits excellent styrene epoxidation with 87.7% styrene oxide selectivity at near‐complete conversion using O 2 and isobutyraldehyde at 50°C, while excess coordinative vacancies per Ce site reduce styrene oxide selectivity to 73.4%. Furthermore, F‐substituted UiO‐66 outperforms terephthalate (67.5%) and 2‐methylterephthalate (60.7%) analogs, and CeO 2 (54%). Mechanistic studies reveal that isobutyraldehyde initiates binding to defective Ce site, deprotonating and reacting with O 2 to generate peroxo radicals that favor styrene vinyl C═C bond adsorption. Concurrently, vinyl C═C bond and adjacent defective Ce site co‐interact with O 2 to form robust Ce─O bond, where activated O 2 undergoes configuration transition from linear to side‐on, inducing dynamic switching of carboxylate groups between bidentate and monodentate coordination; meanwhile, F‐substituted UiO‐66 facilitates peroxo O─O cleavage and vinyl π bond cleavage, enhancing styrene oxide selectivity over H/CH 3 counterparts. Substantially, F‐substituted UiO‐66 enables efficient epoxidation of diverse alkenes under mild condition.