Catalytic Relevance of MgAlO Surface Functionalities in the Upgrade of Ethanol to Butanol
Abstract
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.