Ionic liquids  (ILs) as novel functional desulfurization materials have attracted increasing  attentions. Metal-based ionic liquids (MILs) are classified into three types of  metal chloride ILs, metal oxide ILs, and metal complex ILs based on the  definition and basic structure of MILs in this critical review. On the basis of  the properties of ILs such as structure designability, super dissolution  performance, good thermal and chemical stability, nonflammability, and wide  electrochemical window, MILs exhibit unique advantages on hydrophobicity,  oxidation performance, and Brönsted–Lewis acidity. Therefore, MILs possess both  the absorption and oxidation centers for the intramolecular adsorption and  oxidation to improve the oxidative desulfurization (ODS) process. During the  novel nonaqueous wet oxidative desulfurization process (Nasil), H2S  can be oxidized into elemental sulfur with hydrophobic MILs, which can be  regenerated by oxygen for recycle, to solve the problems of low sulfur capacity,  low sulfur quality, and severe secondary pollution in the aqueous Lo-Cat wet  oxidative desulfurization process. Another outstanding feature of MILs in ODS is  biomimetic catalysis, which has the function of activating molecular oxygen and  improving the oxidation performance. Metal oxide ILs and metal complex ILs are  used in combination with hydrogen peroxide or oxygen with the existing water to  generate a Fenton-like reaction to convert hydrophobic organic sulfur or SO2 into  hydrophilic sulfoxide/sulfone or sulfur acid, respectively. However, the  corrosion of Cl– to  the equipment and emulsification phenomenon in the extraction process of  sulfoxide/sulfone separation still need further study. Furthermore, the  promising strategies to construct highly efficient and green desulfurization  processes for large-scale applications are provided.

The  Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.0c05855.

• Table S1:  Characterization of properties and structure of metal chloride ILs. Table S2:  Characterization of properties and structure of metal oxide ILs. Table S3:  Characterization of properties and structure of metal complex ILs. Table S4:  Oxidative desulfurization of organic sulfide in metal chloride ILs over the past  decade. Table S5: Oxidative desulfurization of organic sulfide in metal oxide  ILs over the past decade. Table S6: Oxidative desulfurization of organic sulfide  in metal complex ILs over the past decade. Table S7: Oxidative desulfurization  of H2S  in MILs over the past decade. (PDF)