Sustainable CO2 valorization via solvent-free cycloaddition over Co(III)-substituted Keggin-type heteropolytungstate encapsulated in iron-based MIL-100

Abstract

The sustainable design of heterogeneous catalysts that simultaneously capture and convert CO2 remains a central challenge in green chemistry. Herein, we report a facile and eco-friendly strategy for the aqueous encapsulation of cobalt(III)-substituted Keggin-type heteropolytungstate (K5[CoW12O40], Co-HPW) into the mesoporous MIL-100(Fe) framework at 60 °C under ambient pressure, avoiding the need for autoclaves or high-temperature hydrothermal synthesis. The resulting hybrid, Co-HPW@MIL-100(Fe), was thoroughly characterized by PXRD, FTIR, BET, SEM, TEM, TGA, and ICP, confirming structural integrity and successful polyoxometalate (POM) incorporation. Benefiting from the synergistic interplay between the redox-active Co-HPW and the CO2-adsorptive MIL-100(Fe) matrix, the composite catalyst exhibited high catalytic activity for the solvent-free cycloaddition of CO2 with epoxides. Under optimized conditions, conversions of 86–92% and selectivities of up to 92% were achieved across a broad substrate scope, with a notable turnover frequency of 1380 h−1 for epichlorohydrin. Moreover, Co-HPW@MIL-100(Fe) retained over 83% of its catalytic efficiency after five consecutive runs with negligible Co-HPW leaching (<2%). This scalable, recyclable, and highly efficient POM@MOF platform offers a promising route for sustainable CO2 valorization via green catalytic processes. © 2025 Elsevier B.V.