Metal–organic frameworks (MOFs) are known for their high crystallinity and high porosity. The well-defined structure makes it possible to study MOF materials on the atomic scale. However, the well-defined structures of MOFs also limit the pore sizes and pore architecture. For example, the pore sizes usually range from 1.0 nm to 10.0 nm, most of the reported MOFs are microporous. The architectures of MOF pores are also limited to channels (square, hexagonal, trigonal, etc.) and cages (tetrahedral, octahedral, cube, cuboctahedral, etc.). Though the combination of metal centers with organic ligands could potentially result in unlimited numbers of structures, the type of pores, pore sizes, and pore surfaces are very limited. It is vital to develop MOF materials that possess hierarchical pores. Hierarchically porous MOFs would contain assorted pore sizes, pore shapes, and pore surfaces, as the metal centers and the organic linkers are connected in a more random fashion.<br/>We have developed a facile synthesis method to prepare hierarchically porous MOFs (HP-MOFs) with low crystallinity. These materials formed through the interconnection of MOF nanocrystals to form larger nanoparticles. The nanoparticles contain pores ranging from several angstroms to several nanometers. Such materials could be realized using very simple organic linkers such as terephthalic acid. HP-MOFs are excellent catalysts themselves as the low crystallinity guarantees the missing linker or missing metal defect, which generates catalytic active centers. HP-MOFs are also ideal candidates as supports to prepare multifunctional catalysts. As there are missing linker sites, ligands with secondary metal centers, such as bipyridine-based and porphyrin-based linkers, could be incorporated into HP-MOFs through post-synthetic modifications, and metal salts could be directly introduced into HP-MOF pores as there are missing metal defects as well. We have prepared HP-MOFs containing active centers through both linker incorporation and secondary metal incorporation. These HP-MOF-supported catalysts have been studied for several emerging reactions, such as epoxidation reaction, CO<sub>2</sub> fixation reaction, hydrogenation reaction, and coupling reactions.

Hierarchically porous metal–organic framework supported catalysts, preparation, properties, and performance

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