Metal–Organic Frameworks as Well-Defined Crystalline Heterogeneous Catalyst Supports

Goetjen, Timothy

doi:https://doi.org/10.21985/n2-061a-wk44

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Metal–Organic Frameworks as Well-Defined Crystalline Heterogeneous Catalyst Supports

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Industrial processes heavily rely on catalysts to control product selectivity and lower energy barriers required for chemical transformations. Catalysts are most commonly solid heterogeneous catalysts that facilitate separations from reaction mixtures and enhance recyclability. Heterogeneous catalysts used in industrial processes exhibit efficacious results, but in certain instances drawing structure-function relationships proves difficult. Without a clear picture of the catalytically active site structure, the exact mechanisms behind the observed catalytic results cannot be derived, which inhibits the development of next-generation catalysts. Metal–organic frameworks (MOFs) are highly crystalline, porous materials constructed by organic linkers connected to metal nodes that self-assemble into multi-dimensional networks. Given their uniform structures and modular nature, MOFs are ideal materials as structurally well-defined catalysts or catalyst supports. MOFs have a wide variety of catalyst siting strategies including but not limited to 1) installation of active metal species at the metal oxide node via reactive hydroxyl and aqua ligands, 2) installation of active metal species into an organic structural linker, and 3) encapsulation of molecular or nanoparticle catalysts within the pores of the framework. Single crystals of certain MOFs can be grown and therefore catalyst structures can be determined at an atomic level by experimental X-ray diffraction measurements. Even bulk spectroscopic measurements become relatively easier to analyze when dealing with more structurally well-defined materials. With the onset of increased availability of “wet” shale gas, hydrocarbon transformations combining small chain molecules rather than breaking down crude oil has received higher interest. Therefore, reactions involving carbon-carbon coupling have gained more interest, and the fundamental understanding of those reaction mechanisms is widely desired. In my research, I aimed to develop MOF-supported catalysts for different carbon-carbon coupling reactions and take advantage of the structural uniformity of MOFs to build platforms to derive structure-function relationships wherever possible, to provide that knowledge for those who are developing next-generation catalysts. Overall, this work advances the field of heterogeneous catalysis by providing structurally well-defined platforms for identifying trends in reactivity and selectivity in chemical transformations, including mechanistic studies. The knowledge gained and subsequent use of platform methodologies will funnel into the development of next-generation catalysts.

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