Amphiphilic Catalysts Comprising Phosphomolybdic Acid Fastened on MIL-101(Cr): Enabling Efficient Oxidative Desulfurization under Solvent-Free and Moderate Reaction Conditions

Abstract

Constructing durable catalysts with high performance offers a novel approach for removing refractory sulfides, such as dibenzothiophene (DBT) and its derivatives, through a catalytic oxidation process. Judging by this strategy, the phosphomolybdic acid ionic liquid was fastened onto the surface pore of MIL-101, which features a large specific surface area and isolated metal sites. Systematic characterization techniques reveal that a good dispersion of the active center on the carrier could be realized, receiving promising catalysts. The as-designed catalyst could inherit the hydrophilicity from the carrier and the lipophilicity from the active center, obtaining a catalyst with an amphiphilic property. Furthermore, the efficient adsorption of sulfides from the oil phase by the carrier could ensure an elevated sulfide concentration on the surface of the amphiphilic catalyst. The two aforementioned distinctive features of the constructed catalyst indicate its promising catalytic oxidation ability for stubborn DBT and its derivatives without the addition of any additional extractant. With optimal reaction parameters, a 99.8% removal of DBT could be accomplished, resulting in oil with a sulfur concentration of less than 1 ppm. Meanwhile, this desulfurization system is also effective for different types of oils. The basically unchanged sulfur removal ability and structure of the catalyst indicate its outstanding durability. Additionally, both the hydroxyl radical and superoxide radical have been verified to play indispensable roles during the desulfurization process.