Enhancing the Catalytic Activity of Zeolitic Imidazolate Frameworks (ZIFs) via an Etching and Regrowth Method for CO2 Cycloaddition Reaction

Zeolitic imidazolate frameworks (ZIFs) bearing rich accessible Lewis acidic/basic active sites and hierarchical pores are favorable to catalyze the cycloaddition of CO₂ and epoxides with high yields of the target product under mild conditions. In this context, a facile etching and regrowth method is developed here to convert unstable leaf-like zinc-based ZIF-L to one kind of bimetallic ZIF (namely, ZnFe-ZIF) with a rough surface, a porous and accessible three-dimensional structure, and abundant Lewis acidic sites. Owing to the high Fe-doping content functioning as rich Lewis acidic sites and the high CO₂ adsorbing capability together with the structural advantages to favor the mass diffusion, the yield of target cyclic carbonate can be up to >99% for the cycloaddition of CO₂ and epichlorohydrin by ZnFe-ZIF at 6 h under mild conditions (0.1 MPa and 80 °C) with the selectivity of 100%. More importantly, unlike ZIF-L, which is unstable in the reaction system, the synthesized ZnFe-ZIF displays a satisfactory chemical stability without a loss in catalytic activities after five recycling runs as well as good substrate tolerance, making ZnFe-ZIF a potential high-performance catalyst for CO₂ conversion.