Catalytic oxidation of thiophene and its derivatives via dual activation for ultra-deep desulfurization of fuels

A catalyst system composed of tungstate and Brønsted acidic ionic liquids (BAILs) was found to be highly active for the oxidative desulfurization (ODS) removal of thiophene, benzothiophene (BT), and their derivatives from model oil using 30 wt.% H2O2 as the oxidant. Five BAILs, [Hnmp]BF4, [Hmim]BF4, [Hnmp]HSO4, [Hmim]HSO4, and [Hnmp][CH3SO3] (nmp = N-methyl-pyrrolidonium, mim = N-methylimidazolium), and various commercial tungstate compounds were investigated. High activity was obtained for the combination of ammonium tungstate and BAILs [Hnmp]BF4. In this catalytic reaction, sulfur content of model oil containing BT could be decreased from 700 ng μL−1 to less than 1 ng μL−1. Turnover frequency (TOF) for BT oxidation is higher than 194 × 10−3 s−1 and that of in non-BAILs [Bmim]BF4 is less than 11 × 10−3 s−1. Noteworthily, the ODS of thiophene, which has been regarded as difficult task, can be also achieved up to 99% conversion with a TOF of 7 × 10−3 s−1. The FT-IR, 1H NMR and electrochemical measurements evidences indicate that the strong hydrogen bonding between the sulfur-containing compounds and [Hnmp]BF4 and the oxidative function of the tungstate synergistically activate the reactants and result in the excellent catalytic performance.