Synergy of photocatalysis and adsorption on TiO₂-CeO₂ for the removal of organosulfur compounds from diesel fuel

TiO₂-CeO₂ mixed oxides were prepared by urea gelation and co-precipitation method and then characterized by N₂ sorption and X-ray diffraction (XRD). The synergy of photocatalysis and adsorption on TiO₂-CeO₂ adsorbents for the removal of organosulfur compounds from diesel fuel was investigated. The results show that the UV irradiation can greatly enhance the adsorption of organosulfur in model fuel on TiO₂-CeO₂; the organosulfur compounds is first photocatalytically oxidized to polar sulfoxides and sulfones over TiO₂-CeO₂, which are then selectively adsorbed on the bifucntional TiO₂-CeO₂ material due to their much higher polarities than the original oranosulfur compounds and other organic compounds in the diesel fuel. The TiO₂-CeO₂ material with a Ti/Ce molar ratio of 9:1 and calcined at 500℃ exhibits the highest synergistic photocatalysis-adsorption desulfurization performance; over it the sulfur removal rate reaches 99.6% for a model fuel after reaction for 5 h under UV irradiation. The low desulfurization selctivity because of the strongly competitive adsorption of aromatics in the diesel fule could be greatly improved by employing the synergistic photocatalysis-adsorption desulfurization process; the sulfur removal rate is still higher than 96.6% for the model fuel containing 25% toluene after reaction for 7 h under UV irradiation. The desulfurization performance of TiO₂-CeO₂ for different organosulfur compounds in the diesel fuel follows the order of 4, 6-DMDBT > DBT > BT. Moreover, TiO₂-CeO₂ can be well regenrated by washing with acetonitrile followed by heat treatment in air; it still gives a high synergistic photocatalysis-adsorption desulfurization performance even after four regeneration cycles.