Catalytic strategies for chemical synthesis and biomass valorization
Open AccessThe implementation of Green chemistry has seen a significant movement towards the design of safer chemicals and sustainable processes. Our efforts have taken to the development of catalysts that can be used in the synthesis of new chemicals, as well as conversion of renewable feedstocks. We report a one-step reproducible synthetic protocol for palladium (Pd) supported on hydrotalcite (HT) catalysts. The results show that the Pd-HT catalysts are electronically and physically tuned by changing the metal composition as well as the metal ratio. We discuss the structural-property-activity relationships of these materials considering the support influence on the electronic property, Pd speciation and catalyst stability. For comparison, Pd supported on non-tunable supports such as activated carbon, silica, magnesium oxide and aluminum oxides were also synthesized and studied. The differences observed for these catalysts result in interesting hypotheses for their catalytic activity in several chemical reactions such as acceptorless amine dehydrogenation, aldol condensation, decarbonylation and transfer hydrogenation – all of which are relevant in the conversion of biomass feedstocks. This work in the transformation of the biomass-derived substrates led to the screening of a series of homogeneous catalysts in the process of upgrading of glycerol into more value-added chemicals via transfer hydrogenation. Implications of this work and needed extensions thereof are discussed in the context of meeting needs for chemical processing for a circular economy.Chapter 1 introduces green chemistry, its history, challenges, and opportunities. The core of this new field is in the word ‘design’ and we address the efforts undertaken in applying the green chemistry principles. Heterogeneous catalysts are also discussed. Chapter 2 explores the development of tunable Pd heterogeneous catalysts using HT as a support. The catalysts are fully characterized and the effect of incorporation of different transition metals in the cationic sheets of the support matrix is addressed. We further attempt to study the effect of changing the aging temperature, model of heating and the cation ratio on the crystallinity, morphology, texture, and particle size on the materials.Chapter 3 studies the catalytic activity in the acceptorless dehydrogenation of secondary amines as well as dehydrogenative primary amine coupling towards catalytic imination. Detailed studies in effect of Pd weight percent on the catalyst is discussed. We demonstrate that by adjusting the conditions in this reaction, high product selectivity can be achieved using Pd-doped HT catalysts.Chapter 4 builds on the dehydrogenative primary amine coupling for catalytic amination. We demonstrate an approach in using Pd speciation and a hydrogen-donor solvent to drive the selectivity in this reaction. The catalyst recyclability is also further added in this chapter.Chapter 5 explores the cooperative workings of supported catalyst through their activity in deoxygenative olefination of aldehydes via a stepwise aldol condensation – decarbonylation reaction. The support properties are also discussed in this chapter. Chapter 6 builds on the dehydrogenative olefination strategy by expanding this reaction to alcohols which are biomass-derived feedstocks. This proceeds via dehydrogenation to produce aldehyde that undergoes aldol condensation then decarbonylation and eventually transfer hydrogenation. The versatility of these cooperative catalysts allows for a broad application in different chemical transformations. This chapter also addresses the challenges of these materials in a multi-step reaction that results in poor selectivity.Chapter 7 studies the expansion of the ‘design’ concept in Green chemistry by looking at a different catalyst design of organometallic complexes. The application of these ‘new’ catalysts are explored in the transfer hydrogenation of carbon dioxide and carbonate salts using glycerol to produce formic acid and lactic acid.Chapter 8 evaluates the major challenges and great opportunities associated with the work described in this thesis. These challenges and opportunities are linked with potential furthering of our current approaches and expanding their applications. With the rapid development of modern chemical techniques, computer science as well as data science, our careful stepwise approaches are showing great potential on their way of expansion.
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Ainembabazi_gwu_0075A_15270.pdf | 2020-09-08 | Open Access |
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