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

Zeolitic imidazolate frameworks (ZIFs) bearing rich accessible Lewis acidic/basic active sites and hierarchical pores are favorable to catalyze the cycloaddition of CO 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 CO 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 CO 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 CO conversion.