Biomimetic catalytic aerobic oxidative desulfurization of diesel with NHPI-based ternary deep eutectic solvents

Abstract

It is a challenging issue to achieve efficient aerobic oxidation desulfurization (AODS) under mild conditions. Inspired by respiratory chain system, a metal-free biomimetic system was developed in this paper with a functionalized ternary deep eutectic solvent (DES) containing N-hydroxyphthalimide (NHPI), p-toluene sulfonic acid (p-TsOH), and polyethylene glycol (PEG) for deep oxidative desulfurization. It was found that the NHPI/5PEG4000/p-TsOH system exhibited an outstanding desulfurization activity, and the removal of dibenzothiophene (DBT) reached 100% within 5 h at 80 οC. Significantly, it is the first attempt to use a DES as an extraction agent, reaction medium, catalyst, and electron transfer mediator (ETM) simultaneously. Mechanistic studies revealed that NHPI demonstrated a dual function: namely, producing the PINO radical to initiate the reaction, and acting as an ETM in biomimetic systems to promote the activation of oxygen molecules, thereby finely improving the AODS performance of the acidic DESs. These findings regarding the aforementioned biomimetic oxygen activation mechanism of the NHPI-based ternary DES for AODS provide a novel insight into the construction of biomimetic system in the future.