Oxidative desulfurization of model diesel via dual activation by a protic ionic liquid

•A protic ionic liquid, [Hnmp]HCOO, was used as in ODS.•The mechanism of ODS was involved in dual activation by the PIL.•The [Hnmp]HCOO exhibited high catalytic activity in ODS.•The amounts of PILs and oxidant dosage play vital roles in desulfurization system.•This system can be recycled five times with an unnoticeable decrease in activity. A novel and green carboxylate-anion-based protic ionic liquid (PIL), [Hnmp]HCOO, was prepared through a simple and atom economic neutralization reaction between N-methyl-2-pyrrolidonium (NMP) and formic acids. Both FT-IR spectra and 1H NMR confirmed its simple salt structure. [Hnmp]HCOO exhibited so high catalytic activity that the dibenzothiophene (DBT) removal reached 99% at 50°C in 3h under conditions of VPIL/Vmodel oil=1:10 and H2O2/DBT (O/S, molar ratio)=5. The catalytic oxidation reactivity of S-compounds was found to be in the order of DBT>4,6-dimethyldibenzothiophene (4,6-DMDBT)>benzothiophene (BT). The investigation on mechanism showed that oxidative desulfurization was realized through dual activation of PIL. Moreover, [Hnmp]HCOO can be recycled for five times with an unnoticeable decrease in desulfurization activity.