For the first time, creation of oxygen defects in the crystalline structure of WO3/SBA-15 catalysts and its correlation with Lewis acidity and catalytic activity in the oxidation of 4,6-dimethyl­dibenzothiophene (4,6-DMDBT) in a model diesel were reported. All the WO3/SBA-15 catalysts predominantly contained Lewis acid sites and some oxygen defects in the crystalline structure of WO3. The oxygen defect concentration increased from 1.67% to 16.66% per lattice cell unit, and the number of Lewis acid sites varied from 92 to 458 μmol/g as the WO3 content increased from 5 to 25 wt %. The 4,6-DMDBT conversion was almost proportional to both the number of Lewis acid sites and oxygen defects. Formic acid addition led to formation of peroxyformic acid which coordinated with surface W6+ to generate reactive oxygen species like peroxometallic complex, improving oxidant stability and 4,6-DMDBT oxidation efficiency. More than 99% of 4,6-DMDBT was removed with the best 25 wt % WO3/SBA-15 catalyst within 15 min of reaction under the optimal condition. A reaction mechanism involving peroxometallic complexes formation, 4,6-DMDBT molecules adsorption, and surface oxidation reaction on structural defects and vanadia nanoparticles was proposed. This biphasic reaction system consisting of a catalyst bearing Lewis acid site, a green oxidant, an oxidant promoter, and a polar solvent would simultaneously perform the oxidation and separation of polyaromatic sulfur compounds in one operation which was very practical for ultralow sulfur diesel production.

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A sepiolite from Vallecas (Spain) was treated with solutions of HC1 (1.25, 2.5, 5.0, 10.0 and 20.0 wt%) at 25°C for 2, 6, 24 and 48 h, respectively. The resulting solids were characterized by XRD, FT-IR and thermal analyses, along with SEM, TEM and nitrogen adsorption isotherms at 77 K. The free silica was digested and determined in all samples. Several samples were seen to have specific surface areas up to 450 m2/g, with a maximum value of 549 m2/g in the sample treated with 1.25 wt% HCl for 48 h. A sudden decrease in specific surface areas was observed when free silica was digested.

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