Factors Affecting the Selective 5-Hydroxymethylfurfural Electrooxidation to 5-Formyl-2-furancarboxylic Acid over Amorphous CoO x Catalyst

High Resolution Image Download MS PowerPoint Slide The utilization of renewable energy and mild synthesis conditions has recently garnered increased interest for the electrochemical conversion of 5-hydroxymethylfurfural (HMF) into high-value chemicals. However, the deep oxidation of the alcohol group (−OH) while protecting the aldehyde group (−CHO) of HMF made the selective electrooxidation to 5-formyl-2-furancarboxylic acid (FFCA) challenging. Herein, three overall operating factors (applied potential, temperature, and HMF concentration) governing partial and deep oxidation of the alcohol group of HMF were investigated; thereby, the selective formation of FFCA in borate electrolyte (pH 9.5) over CoO x electrocatalyst was achieved. At room temperature, the applied potential could regulate the partial to deep oxidation ratio of the −OH group of HMF, thereby allowing high selectivity of FFCA but leading to a low total Faradaic efficiency (FE) at the high applied potential. The temperature was the most significant factor affecting product distribution, causing both cathodic shifts in onset potential and deep −OH group oxidation, resulting in higher FFCA selectivity at high temperature. The HMF concentration was found to have an insignificant influence on the −OH group oxidation process but caused HMF electrooxidation (HMFOR) to be more effective. Accordingly, HMFOR on CoO x in a pH 9.5 electrolyte at 50 °C achieved a total FE of 70% and yielded FFCA as the main product with a selectivity of 60%. Our study provides insight into the simple approach to control the oxidation process of the −OH group of HMF, hence facilitating future research in this domain, especially in refining reaction conditions for the selective large-scale synthesis of targeted products.