Metal-based ionic liquids and solid-loaded catalysts in fuel oil desulfurization: A review

Metal-based ionic liquids (MILs) have the advantages of designability, efficiency, stability, and regenerative cycle and can efficiently convert thiophene and its derivatives, which are important for the production of "ultra-low sulfur" oils. This paper provides an overview of the research progress of MILs in the field of fuel desulfurization, focusing on the current status of MILs and solid-loaded MILs catalysts in extractive desulfurization, oxidative desulfurization, extraction-catalyzed oxidative desulfurization, and catalytic-adsorption desulfurization processes. For MILs, the anion and cation can be altered by design so as to impart specific functions. Loading is one of the effective ways to solidify MILs, and the combination of MILs with different carriers can not only reduce the usage while ensuring the catalytic activity but also improve the reusability of the catalyst. The combination of MILs with specially structured carriers also allows solution-free adsorption and removal of oxidation products. Compared with conventional MILs, polymetallic-based ionic liquids (PMILs) exhibit ultra-high catalytic activity and are one of the most promising materials available, but are still in their infancy in the field of fuel catalysis, and researchers are needed to enrich the gap in this field. Finally, some problems faced by various types of MILs are pointed out in order to design new functional MILs catalysts with better properties in the future and promote the further development of MILs in the field of fuel catalysis.