Synthetic Origin-Dependent catalytic activity of Metal-Organic Frameworks: Unprecedented demonstration with ZIF-8 s on CO2 cycloaddition reaction

• Only ZIF-8 synthesized in an aqueous medium exhibited marked catalytic performance. • Water occluded in ZIF-8 led to Zn-N bond dissociation, creating active components. • Dissociated N species (pyrrolic or pyridinic) were inactive toward CO 2 cycloaddition. • In addition, Zn species bound with hydroxyl groups were formed. • The newly formed Zn species working as Lewis acid/base was key to CO 2 cycloaddition. In this study, the catalytic activities of three types of zeolitic imidazolate framework-8 (ZIF-8) (two types were synthesized in aqueous and methanolic media, while the other was commercially available) with respect to CO 2 cycloaddition to epichlorohydrin were evaluated. Surprisingly, only the ZIF-8 that was synthesized in an aqueous medium showed a marked catalytic performance, leading to the generation of the desired product, chloropropene carbonate. On the contrary, the other two types of ZIF-8 showed little to no catalytic activity. It is conjectured that the water molecules occluded inside the as-synthesized ZIF-8 triggered the dissociation of Zn-N bonds, resulting in a concomitant transformation to a new, dense phase. Accordingly, it is plausible that dissociated Zn or N species were formed during the reaction. In particular, we found that the dissociated N species arising from the dissociation of Zn-N bonds were pyrrolic and pyridinic, while the dissociated Zn species were bound to hydroxyl groups. Finally, complementary interpretation of CO 2 – and NH 3 -based temperature-programmed desorption and NH 3 -adsorbed Fourier transform infrared spectroscopy results revealed that the dissociated Zn species connected with hydroxyl groups, observed only in the ZIF-8 synthesized in an aqueous medium, served simultaneously as Lewis acids and bases and, thus, were crucial to the CO 2 cycloaddition reaction.