Unveiling structure-function relationships in deep eutectic solvents based biomimetic catalysis for aerobic oxidative desulfurization

Organic sulfides in fuel oil result in the formation of environmentally hazardous sulfur oxide through the combustion in vehicle engine. Oxidative desulfurization is considered to be an effective technique to eliminate sulfides in fuel oil, whose core is the construction of efficient catalytic systems under mild conditions. Herein, a biomimetic catalytic system was designed for aerobic oxidative desulfurization via coupling ammonium molybdate polyoxometalate with four different deep eutectic solvents (DESs), obeying multi-step electron transfer mechanism. It was found that the desulfurization efficiency was not directly associated with conductivity, viscosity and hydrogen-bonding strength. In combination with density functional theory (DFT) calculation, the difference in desulfurization efficiency was ascribed to the distinguished intrinsic oxidation ability of organic acid in DES. The optimal catalytic system not only could resist the adverse effect of naphthaline and indole within suitable concentration scope, but also did not show obvious decrease in desulfurization performance after ten runs. More importantly, deep desulfurization was still afforded for actual diesels using this catalytic system, indicating its enormously potential applications on an industrial level under mild conditions.