A number of phosphomolybdic acid dispersed on SBA-15 polyoxometalate catalysts with structural defects were synthesized and applied for the production of ultralow sulfur diesel. The oxygen defects in the catalysts were quantitatively determined by the Rietveld refinement method. These catalysts contained many surface acid sites including Brønsted (B) and Lewis (L) acid sites (648 to 1479 µmol/g), depending of the heteropolyacid content and the thermal treatment. The area under the IR absorption band at 980 cm-1 (the characteristic of the Mo=O bond) in the FTIR spectra of different catalysts was found to be inversely proportional to the variation of L acidity as a function of temperature, indicating that oxygen defects are the origin of the L acidity. In the oxidation reaction for removing dibenzothiophene, DBT, from a modal diesel, the DBT conversion correlated well with the oxygen defect concentration and total surface acidity, confirming that the surface acidity and oxygen defects played the key roles in DBT adsorption and oxidation. Almost 100% DBT conversion was achieved on the best 30wt%H3PMo12O40/SBA-15 catalyst under the optimal reaction condition (reaction time 60 min, reaction temperature 70°C, H2O2/DBT molar ratio 6-8, catalyst concentration 2-2.5 mg/mL, formic acid/H2O2 molar ratio 1.5). A novel mechanism of the DBT oxidative removal in a biphasic system involving the participation of the neighboring L and B acid sites, oxygen defect, and the formation of active polyoxometalates has been proposed.

You have access to this article

Please wait while we load your content... Something went wrong. Try again?