Development of Supported Catalysts for Valorization of Renewably-Sourced Chemicals
Open AccessThe rise in popularity of green chemistry has simulated new interest in catalytic process that can be used to upgrade renewably-sourced chemicals and generate value- added chemicals through the minimal use of fossil fuel sources. To this end, we strive to develop sustainable catalytic process, which can help facilitate a circular economy of chemicals by allowing for the conversion of renewable feedstocks and the re-use of chemicals to minimize energy input, waste production and consumption of precious metals.We report the protocols for the use of layered double hydroxides (LDHs), such as hydrotalcites, as supports for single-site heterogeneous catalysts (SSHCs) or atomically- dispersed supported metal catalysts by using a one-step reproducible synthetic method. The catalyst design is based on tuning the supported catalysts by changing the compositions of the LDH supports through doping with different transition metals, which modifies the surface acid-base properties significantly. We also study the electronic support effects on SSHCs and thermal stabilities of supported catalysts. The resulting palette of catalysts are characterized to establish the relationship among catalysts structure, properties and reaction reactivity/selectivity. The single-site catalyst consists of Ir organometallic precursors composed of N-heterocyclic carbene ligands.These SSHCs have been applied to transfer hydrogenation and acceptorless dehydrogenation of biomass-relevant substrates, including glycerol, levulinic acid, and most recently, glucose and cellulose. Glycerol is converted to lactic acid, with ability to transfer released hydrogen to CO2 or CO32- to form formic acid, or levulinic acid, to form γ-valerolactone (GVL). We demonstrate the methods for efficient catalytic processes by using microwave-accelerated system, hydrothermal reactors and a continuous flow system. We report the study of kinetics, mechanisms, and stability in order to inform further development of industrially-relevant catalysts for this process.Chapter 1 introduces green chemistry fundamentals, including concepts, history, challenge, and opportunities. Strategies of designing catalysts related to green chemistry and principles of designing catalytic processes for a circular economy are also addressed. Chapter 2 reviews precedent research on the valorization of a waste alcohol feedstock, glycerol, to value-added product, lactic acid, from a catalyst-design perspective and proposes a framework for the design of new processes that enable circular economy. Chapter 3 discusses the design of hydrotalcite-supported single-site heterogeneous catalysts and investigation of their structure-property-activity relationships. In Chapter 4 we describe the performance of these catalysts for batch reactions and continuous flow reactions. Finally, Chapters 5-7 show the application of these catalysts to the valorization of other biomass-derived substrates or waste chemicals to value-added products.
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