A series of Lewis acidic ionic liquids (ILs) based on 1-n-butyl-3-methylimidazolium metal chloride, i.e., [C(4)min]Cl/MCl2 (M = Zn, Fe, Cu, Mg, Sn, Co), are synthesized and used to investigate the oxidative removal of sulfur compounds (S-compounds) from diesel fuels, with ILs serving as both extractant and catalyst and 30 wt% H2O2 solution as oxidant. It is observed that metal chloride species affect S-removal, as S-removal efficiency follows the order: [C(4)mim]Cl/ZnCl2 > [C(4)mim]Cl/FeCl2 > [C(4)mim]Cl/CoCl2 > [C(4)mim]Cl/MgCl2 > [C(4)mim]Cl/CuCl2 > [C(4)mim]Cl/SnCl2. The highly efficient [C(4)mim]Cl/SnCl2 is selected to investigate the effects of ZnCl2 content on desulfurization. It is interesting to find out that ZnCl2 content has a significant influence on desulfurization; specifically. 99.9% S-removal is observed for [C(4)mim]Cl/3ZnCl(2) after 3 h at 45 degrees C, O/S molar ratio of 8, IL/oil mass ratio of 1/2. [C(4)mim]Cl/3ZnCl(2) then undergoes series of parallel experiments to systematically investigate the influence of factors such as temperature, molar ratio of O/S, mass ratio of IL/oil, and ILs recycling. The incorporation of real diesel fuel into this study demonstrates the efficacy of this IL in desulfurization. This work shows that oxidative desulfurization using Lewis acidic ILs may be a new option for producing cleaner diesel fuels. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.