Doctor of Philosophy
Chemical and Biochemical Engineering
The catalytic upgrading process of ethanol to n-butanol can not only increase the economic value of bioethanol, but also address current sustainable fuel needs. The process involves a complex reaction network, encompassing undesired side reactions, making the design of the catalytic system extremely challenging. These problems must be addressed before the ethanol to butanol process can become industrially relevant. In this dissertation, we used hydrotalcite-derived mixed metal oxides (MgAlO) based catalysts to understand the issues associated with the ethanol upgrade to butanol process and adjusted the catalyst structure and active sites through changes in the Mg/Al ratio and introduction of additional redox metal oxides functionalities. By performing a series of reaction activity tests, kinetic experiments, in situ UV/Vis and FTIR characterization, TPR, TGA and in situ active center titration, qualitative and quantitative relationships between catalyst structure and catalytic performance are obtained. We found the MgAlO mixed metal oxide system can catalyze the ethanol to butanol process through a Guerbet reaction pathway, though the process is kinetically limited. By introducing suitable redox metal oxides to the catalyst formulation, such as MoO3 and V2O5, this problem can be eased out, but at a cost of losing a significant fraction of strong basic centers. More crucially, we identified that the number of these strong basic centers are the most catalytically relevant function in the MgAlO material, as they controlled enolate formation, which is the rate limiting step of the aldol condensation kinetic bottle neck in the Guerbet reaction.
Summary for Lay Audience
Ethanol is the most common biofuel, used widely in the transportation section, specifically as gasoline additives. The current transition to electric-based cars anticipates an oversupply of renewable bioethanol in the market. This thesis explores the possibility of directly converting ethanol to n-butanol, a more efficient energy carrier, and fine chemical precursor.
The transformation of ethanol to n-butanol is a chemically complex process, that requires a stringent tunning of reaction events, where C-H, C-C and C-O chemical bonds are breaking and forming in a tandem sequence that needs to be carefully regulated. On this dissertation a set of MgAlO (hydrotalcite) derived materials is selected to accelerate the chemical reactions leading to butanol formation of ethanol, and a carefully detailed study at the molecular level is carried out using spectroscopic and chemical kinetic tools. This with the aim to elucidate the critical functions on the material that are responsible for a successful (or unsuccessful) reaction even leading to the conversion of ethanol to butanol. The results indicate that functionalities in the hydrotalcite material, able to abstract H+ ion from ethanol regulate the conversion of ethanol to butanol over hydrotalcite derived materials.
Tian, Wei, "Catalytic Relevance of MgAlO Surface Functionalities in the Upgrade of Ethanol to Butanol" (2023). Electronic Thesis and Dissertation Repository. 9478.
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