MOF engineering towards Lewis base heterogeneous catalysts David Villalgordo Hernández , Javier Narciso, E.V. Ramos-Fernández a Department of Inorganic Chemistry, Institute of Materials of the University of Alicante (IUMA) david.villalgordo@ua.es In the search for novel materials for a wide range of applications such as gas adsorption and separation, heterogeneous catalysis, electrocatalysis, photocatalysis or even acting as drug dealing agents; MOFs have been lately emerging as an appealing alternative to classic materials such as zeolites, metal-supported carbons or ceramic metallic-oxides. The rising interest in the MOFs field appear especially due to its immense variability thanks to the possibility of obtaining MOFs by coordination of a vast amount of metal cations and organic molecules. This allows for the strategic design of MOFs in order to make them suitable for a selected application. Some families of MOFs present an inherent property that makes them fit as heterogeneous catalyst in several reactions. That is having both Lewis acid and basic sites simultaneously. Since MOFs are formed by metal cations or metal oxide clusters, hence groups that act as Lewis acid sites, as well as some organic linkers (i.e.: imidazolates) can present basic groups. Zeolitic Imidazolate Frameworks (ZIFs) consist of metal cations tetrahedrally-coordinated to imidazolate (Imz) groups, generating an Imz-M-Imz unit with an angle similar to that of a Si-O-Si in zeolites. Several strategies have been developed in order to modify MOFs properties with the aim to improve a determined characteristic that makes them suitable for a selected application. Post-synthetic modification (PSM) appears as one of the most relevant strategies for this purpose. Once a MOF is obtained, it is furtherly modified by another process such as linker exchange. In this case, the original MOF’s linker is partially exchanged with another linker. Therefore, in this work ZIF-67 (Co(imz) 2 : imz = 2-Methylimidazole) is modified post-synthetically by linker exchange. In order to obtain an improved Lewis basicity effect on a ZIF-67, a post-synthetic approach has been utilized by exchange of 2-methylimidazole linkers with 1,2,4-triazole. Following this procedure, a series of partially exchanged ZIF-67 have been obtained. In this case, triazoles greatly enhance the amount on N uncoordinated sites, which can act as Lewis basic sites. Thereafter, this MOF could be tested in base-catalyzed reactions such as CO 2 cicloaddition, formose reaction or utilized as an adsorbent in the CO 2 /CH 4 separation.
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