Heterogenous carboxyl-functionalized bilayer ionic liquids/polyoxometalate catalysts for extractant-free oxidative desulfurization

Abstract

Heterogenous carboxyl-functionalized bilayer ionic liquids/polyoxometalate catalysts were synthesized. The optimized catalyst SiO2(50 nm)-BiIL-PW(Keggin-type) was characterized via FT-IR, XRD, Raman, UV–vis-DRS, XPS, TG, SEM-EDX, TEM, contact angle and N2 adsorption/desorption. Characterization results illuminate that polyoxometalate anions are grafted successfully onto the surface of carrier. The catalyst exhibits good amphiphilicity for both sulphur-containing compounds and hydrogen peroxide. With optimized catalyst, 100% sulfur removal can all be achieved for four model fuels including less active BT using a 4:1 molar ratio of n(H2O2)/n(S) and a low temperature of 40 °C free of extractant, which could be attributed to the better quasi homogeneous microenvironment provided by bilayer ionic liquids. Reaction results demonstrate that polyoxometalate and carrier have significant effects on the catalytic activities. Keggin-type phosphotungstate and 50 nm silica are superior for the desulfurization. ICP-MS analysis and the characterizations of recovered catalyst show no significant leaching of catalytic active component. No decrease was observed in catalytic efficiency after the 8th cycle in scale-up experiments.