Catalyst design for the transformation of CO2 into value-added products.

The mass-utilization of fossil resources has led to a dramatic increase in carbon dioxide (CO2) production, most of which is released directly into the Earth's atmosphere, resulting in global warming. Efforts to contain CO2 emissions and to capture, store and use this molecule are required to reduce the rate at which the concentration of CO2 increases in the atmosphere. Valorizing CO2 by chemical transformation is valuable as CO2 is abundant, cheap, and considered as a waste molecule. Unfortunately, CO2 is thermodynamically stable and chemically inert and therefore either high energy input or efficient catalysts are required to transform it. This thesis details the design of catalytic systems for the transformation of CO2 into value-added products. First, the consequences of high atmospheric CO2 levels will be presented. Then, the catalytic systems that have been developed for CO2 utilization are reviewed, with emphasis on fuel production and incorporation of CO2 into organic scaffolds. Next, our contributions to the ionic liquid (IL) catalyzed cycloaddition of CO2 into epoxides (CCE reaction) to afford organic cyclic carbonates are compiled. Recent advances in the field of IL catalysts for the CCE reaction are summarized as an introduction to this chapter, followed by a mechanistic investigation on the imidazolium salt catalyzed CCE reaction. Then, the preparation and characterization of polymeric ILs based on a vinylbenzyl functionalized imidazolium salt are described. The ability of the materials to catalyze the CCE reaction is reported. Based on the knowledge gained throughout these studies, a catalytic CO2 extraction reactor was developed containing a simple IL:epoxide mixture that is able to quantitatively extract CO2 from an array of gas streams. Subsequently, the utilization of carbene catalysts for the N-methylation and N-formylation of amines using CO2 as the C1 source and hydrosilanes as the reducing agent is compiled in the form of a protocol. Then, an approach to produce organic cyclic carbonates employing diols rather than epoxides as the starting material is highlighted. The methodology relies on a carbene catalyst that was employed in combination with Cs2CO3 and an alkyl halide that was required to capture the water that is formed during the reaction. Afterwards, the concept of CO2 and H2 activation using an ionic frustrated Lewis pair composed of an IL and B(C6F5)3 is presented. Finally, the knowledge obtained from the N-formylation reaction combined with the cyclic carbonate chemistry allowed us to develop a simple methodology relying on the cooperativity between hydrosilanes and fluoride salts to transform cyclic carbonates into their corresponding diol and methanol. Formally, this methodology allows for the metal-free indirect reduction of CO2 into methanol. Together, our results show that CO2 can effectively be used as a C1 source in an array of chemical reactions, some of which are of industrial importance. Utilizing CO2 as a benign C1 source can lead to the replacement of existing methods that employ toxic and harmful chemicals.

Dyson, Paul Joseph
Lausanne, EPFL

 Record created 2018-06-05, last modified 2019-06-18

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