Defect-engineered MIL-101(Cr) via facile low-temperature calcination for efficient CO2 cycloaddition under mild conditions

Defective metal organic frameworks have emerged as promising catalysts for CO2 conversion owing to their tunable active sites and exceptional catalytic activities. Despite their potential, achieving high defect densities through simple and scalable methods remains a major challenge. To address this, we developed an innovative low-temperature calcination strategy (300 °C, 10 min) to introduce abundant ligand defects into MIL-101(Cr) while maintaining crystallinity, thereby exposing additional Cr3+ Lewis acid sites to participate in epoxide activation. The resulting defective MIL-101 demonstrates remarkable catalytic efficiency in CO2 cycloaddition, achieving a >99% yield under mild conditions (80 °C, 0.1 MPa) within 6 h, significantly surpassing that of pristine MIL-101 (52%). Furthermore, the catalyst exhibited outstanding recyclability, retaining full activity over multiple reaction cycles. In addition to synthetic simplicity, this work provides fundamental insights into the critical role of defects in promoting epoxide activation and ring opening, establishing a sustainable pathway for CO2 utilization under mild conditions and the energy-efficient production of cyclic carbonates.