Abstract
In this investigation, an ultrasound-assisted synthesis method was applied to synthesize the highly dispersed 12-molybdophosphoric acid on SBA-15 catalysts. Three SBA-15-supported catalysts were obtained with varying heteropolyacid content from 10 to 20 and 30wt%. The heteropolyacid exhibited high dispersion on SBA-15, with a particle size smaller than 4 nm, as confirmed by XRD analysis and TEM observation. All catalysts possessed both Lewis (L) and Brønsted (B) acid sites, and the number of acid sites showed an almost linear increase with the heteropolyacid content. In the oxidative removal of 4,6-dimethyldibenzothiopene (4,6-DMDBT) from a model diesel, these catalysts demonstrated high catalytic activity. The 4,6-DMDBT conversion was proportional to the surface acidity, reaching the highest conversion of 98.7% on the catalyst with 30wt% heteropolyacid after a 40 min reaction at 70°C. It was proposed that the 4,6-DMDBT molecule preferentially adsorbed on the L acid sites by donating its unshared electrons in sulphur atom to the L acid sites of the catalyst via the surface acid-base reaction pathway, followed by oxidation reaction with H2O2 oxidant. The resulting polar sulfone (4,6-DMDBTO2) was immediately extracted by the polar extracting agent (acetonitrile) and separated from the oil phase. This work has proven that adsorption, oxidation and separation of 4,6-DMDBT in a model diesel fuel can be simultaneously realized in one operation unit for ultralow sulphur diesel production.
