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This dissertation delves into the exploration of the feasibility of a "Power-to-Fuel" system, aiming to leverage renewable energy for the direct electrochemical conversion of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF). Addressing the core research questions, the study investigates the efficient conversion of α-cellulose to HMF and its subsequent electrochemical reduction to DMF. The electrochemical conversion of HMF to DMF, a less explored domain in the existing literature, poses a significant obstacle. Issues related to the insolubility of DMF in water and accurate product analysis further complicate the research landscape.
Establishing a suitable electrolyte solution with 1 M H2SO4 and 50 wt% acetonitrile introduces challenges related to the instability of key components like 5-methylfurfuryl alcohol (MFA), 2,5-dihydroxymethylfuran (DHMF), and DMF; as well as large solution resistances in the electrochemical reactions. In this work, the main decomposition products of MFA, DHMF, and DMF are identified but not quantified. Exploring a reliable electrocatalyst becomes the focus after setting a proper compensation protocol for the uncompensated solution resistance.
A comprehensive screening of materials, classified into good hydrogen evolution reaction (HER) catalysts and average HER catalysts, highlights the preference for Ag foil as an efficient catalyst for HMF to DMF electrochemical reduction. Further cathode modification attempts with Hg-poisoned Pt foil and oxide-derived Ag foil, as well as the use of AgCu alloy and a tandem Cu and Ag working electrode, prove less effective and visibly unstable compared to conventional Ag foil.
Systematic evaluation of Ag foil is performed by investigating the direct conversion of intermediates (DHMF and MF), the optimal potential range for HMF to DMF reduction, and electrode reusability. Notably, DHMF demonstrates inert behavior during electrolysis, suggesting its status as a terminal product. Electrolysis with MF as a substrate yields up to 50% FE at -0.8 V vs. Ag/AgCl. The absence of MFA in the analyzed samples suggests a direct, one-step MF to DMF conversion. Optimal potential investigations at -0.75, -0.8, and -0.85 V vs. Ag/AgCl reveal nuanced results, showcasing the complexity of the electroreduction process.
Last but not least, this dissertation also explores the acid-catalyzed hydrolysis of water-soluble oligomers (WSO) to glucose and the subsequent isomerization to HMF. While initial attempts with autoclave reactions prove inefficient, microwave-assisted reactions achieve high HMF yields in a rapid and facile manner. The subsequent electrolysis is performed with the as-obtained WSO-derived rich HMF acetonitrile solution. However, the unselective HMF conversion observed in these samples renders the direct conversion of WSO-derived HMF to DMF unlikely in the highly acidic solutions employed in this work.
