Leaching in Specific Facets of ZIF-67 and ZIF-L Zeolitic Imidazolate Frameworks During the CO Cycloaddition with Epichlorohydrin.

Zeolitic imidazolate frameworks (ZIFs) have been profusely used as catalysts for inserting CO into organic epoxides (i.e., epichlorohydrin) through cycloaddition. Here, we demonstrate that these materials suffer from irreversible degradation by leaching. To prove this, we performed the reactions and analyzed the final reaction mixtures by elemental analysis and the resulting materials by different microscopies. We found that the difference in catalytic activity between three ZIF-67 and one ZIF-L catalysts was related to the rate at which the materials degraded. Particularly, the {100} facet leaches faster than the others, regardless of the material used. The catalytic activity strongly depended on the amount of leached elements in the liquid phase since these species are extremely active. Our work points to the instability of these materials under relevant reaction conditions and the necessity of additional treatments to improve their stability.