| Summary: | This review deals with the notable results obtained by the synergy between ionic liquids (ILs) and WO<sub>3</sub> in the field of pollutant gas sensing and sulfur removal pretreatment of fuels. Starting from the known characteristics of tungsten trioxide as catalytic material, many authors have proposed the use of ionic liquids in order to both direct WO<sub>3</sub> production towards controllable nanostructures (nanorods, nanospheres, etc.) and to modify the metal oxide structure (incorporating ILs) in order to increase the gas adsorption ability and, thus, the catalytic efficiency. Moreover, ionic liquids are able to highly disperse WO<sub>3</sub> in composites, thus enhancing the contact surface and the catalytic ability of WO<sub>3</sub> in both hydrodesulfurization (HDS) and oxidative desulfurization (ODS) of liquid fuels. In particular, the use of ILs in composite synthesis can direct the hydrogenation process (HDS) towards sulfur compounds rather than towards olefins, thus preserving the octane number of the fuel while highly reducing the sulfur content and, thus, the possibility of air pollution with sulfur oxides. A similar performance enhancement was obtained in ODS, where the high dispersion of WO<sub>3</sub> (due to the use of ILs during the synthesis) allows for noteworthy results at very low temperatures (50 °C).
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