Polyoxometalate-based ionic liquid catalyst with unprecedented activity and selectivity for oxidative desulfurization of diesel in [Omim]BF4

Abstract

In this study, a novel Polyoxometalate (POM)-based ionic liquid (IL), [3-(pyridine-1-ium-1-yl)propane-1-sulfonate]3(NH4)3Mo7O24·4H2O, abbreviated [PyPS]3(NH4)3Mo7O24, was prepared and employed as a catalyst in the extraction and catalytic oxidative desulfurization (ECODS) of model and actual diesel. The catalyst was characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analyses (TG-DTA) and X-ray photoelectron spectroscopy (XPS). The [PyPS]3(NH4)3Mo7O24 catalyst demonstrates unprecedented activity in oxidative desulfurization system that the removal of dibenzothiophene (DBT) could reach 99% under quite mild conditions (T = 25 °C, n(catalyst) = 0.0056 mmol, t = 60 min, n(H2O2)/n(sulfur) = 3, VIL/VModel Oil = 1/10). Moreover, the catalytic oxidative desulfurization system can work under the extreme reaction condition, i.e., the DBT removal could reach 99% even at 0 °C. Some important parameters which affect the ODS process, such as temperature, hydrogen peroxide dosage reaction systems and different sulfur compounds, were systematically studied. In addition, the catalyst exhibits remarkable selectivity to the catalytic oxidation sulfides compared with monocyclic or di-aromatics. And this desulfurization system could be recycled for five times without significant reducing the desulfurization. Furthermore, the deep catalytic oxidative desulfurization of actual diesel could also be achieved with this oxidative desulfurization system.