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

Abstract

CeO₂ 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 Ce₆-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 O₂ 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 CeO₂ (54%). Mechanistic studies reveal that isobutyraldehyde initiates binding to defective Ce site, deprotonating and reacting with O₂ 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 O₂ to form robust Ce─O bond, where activated O₂ 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/CH₃ counterparts. Substantially, F-substituted UiO-66 enables efficient epoxidation of diverse alkenes under mild condition.