Designing Metal-Organic-Frameworks For Selective Biomass Catalysis
2020-03
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Designing Metal-Organic-Frameworks For Selective Biomass Catalysis
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2020-03
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Metal-organic frameworks (MOFs) are microporous materials with a wide range of pore sizes and functionalities, making them attractive for a variety of potential applications in catalysis, separations, sensing, and gas storage. Associated with the global demand for clean energy sources to find alternatives to fossil fuels, their use as catalysts for biomass conversion to chemicals finds potential application. The performance of MOFs in these applications is dependent on how stable they are upon modifications to their tunable frameworks. Such modifications include acid treatment, ligand, and cluster functionalization that can be performed by direct synthesis or post-synthesis modification, as desired for optimum performance. This dissertation focuses on using synthetic methods that may enable the tailoring the microstructure of MOFs towards their use for catalysis of biomass. We discuss the use of a method called acid modulation to introduce missing-ligands defects and open Lewis acid sites into the framework of UiO-66 to make it an active and selective catalyst for glucose isomerization to fructose in alcohol media. We demonstrate that upon the alcohol choice, the selectivity of the reaction to fructose can change drastically by favoring other reaction pathways. Furthermore, we investigate the reaction mechanism of glucose isomerization into UiO-66 and identify that glucose reacts via a 1,2-hydride transfer mechanism similar to what was reported for Sn-zeolites. We report the synthesis and installation of phosphonic acid moieties into the ligands of UiO-66 and UiO-67 as a way to introduce Brønsted acidity to these materials by a post-synthesis ligand exchange method. The active sites of P-UiO-66 are elucidated by a combination of solid-state NMR and DFT calculations. P-UiO66 is reported to be active and selective for several acid-catalyzed reactions such as alcohol dehydration and furans dehydra-decyclization with site-time yields approaching that of highly selective phosphoric acid zeolites, holding promise for its use in this and other reactions for the biomass conversion to chemicals. The tunability of MOFs combined with the PSM method and synthesis of phosphonic acids can provide accurate control of the density of active sites with a uniform distribution throughout the framework.
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University of Minnesota Ph.D. dissertation. March 2020. Major: Chemical Engineering. Advisor: Michael Tsapatsis. 1 computer file (PDF); xv, 121 pages.
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Dorneles de Mello, Matheus. (2020). Designing Metal-Organic-Frameworks For Selective Biomass Catalysis. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/215146.
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