A new family of dialkylpiperidinium tetrachloroferrate catalysts, such as [C(2)OHmpip]FeCl4, [C(4)mpip]FeCl4, [C(8)mpip]FeCl4, and [C(12)mPip]FeCl4, were synthesized and characterized by FT-IR, Raman, and ESI-MS. Their catalytic activities for oxidation of dibenzothiophene (DBT) in extraction and catalytic oxidative desulfurization system (ECODS) were evaluated using different ionic liquids. Results indicated that the 97.1% removal of DBT was obtained with [C(4)mpip]FeCl4 as catalyst in ionic liquid [C(8)mim]BF4 at 30 degrees C in 60 min. The optimal H2O2/sulfur molar ratio was only 3.5:1, which suggested that the catalyst was one of the most efficient catalysts reported so far. UV-Vis spectra provided an evidence that the lower desulfurization reactivity in PF6--containing ionic liquids was attributed to the strong interaction between ionic liquid and DBT. Through the gas chromatography-mass spectrometer (GC-MS) analysis, dibenzothiophene sulfone was proved to be the only product of oxidation of DBT. Furthermore, the process of ECODS system was confirmed by GC-MS. (C) 2014 Elsevier B.V. All rights reserved.