Deep Eutectic Solvents with Excellent Catalytic Ability for Extractive and Oxidative Desulfurization under Room Temperature

Deep eutectic solvents (DESs) have been intensively investigated as promising green solvents for extraction combined with oxidative desulfurization (EODS) of fuel oil. However, it is still a challenge to explore the effect of hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) structure on the formation of DESs and the performance of desulfurization. In this study, exploratory density functional theory (DFT) calculation was first carried out to reveal the influence of the electron density of HBA on the preparation of DES. Then, the structures of DESs were optimized, and their interaction energy was calculated. The structure of HBA and HBD has an important effect on the formation of DES and the capacity of EODS. Under optimal conditions (30 °C, O/S = 2), the desulfurization efficiency of phenol/formic acid (Ph/FA) DES can reach as high as 99.8%. Further, the desulfurization mechanism was also investigated by experiments, characterizations, and verified DFT calculations. This study not only provides a new aspect for designing and understanding DESs but also provides a novel catalyst for efficient EODS.