Controllable Preparation Of Titanium-based Catalysts And Study On Catalytic Oxidative Desulfurization In Fuel

SOx produced by combustion of sulfide in fuel is one of the major pollutants in the atmosphere.The lower sulfur content will contribute to prevent the poisoning of the catalyst in tail gas treatment device and good for controlling vehicle emission pollutants.Therefore,the sulfur content in vehicle fuel is an important index which needs strict control.Since 2017,our country has fully supplied the gasoline and diesel according with the stage five national standards.The standards limited the sulfur content decreased from 50 ppm to 10 ppm,deep desulfurization has become an important task in the refining industry.At present,ODS is considered as one of the most promising methods because of its mild reaction conditions,low cost,simple to operate and high catalytic efficiency to aromatic sulfide that hard to remove by hydrodesulfurization technology.A high catalytic efficiency and low cost ODS system is working out to realize the aim of deep desulfurization.In this paper,the catalytic oxidative desulfurization system is consisted of a series of,anatase TiO₂ as active center,titanium based catalysts and 30 wt.%H₂O₂ as oxidant.Meanwhile,it has been used to investigate the desulfurization activity of the model oil with various of dibenzothiophenic sulfides.The primary researches in this paper include the following three parts:1.a series of TiO₂ nanoparticles catalysts with various dispersions were prepared via hydrothermal treatment combined with calcination.Compositions and structures of the as prepared samples were analyzed by means of wide-angle X-ray diffraction（XRD）,Raman,Transmission electron microscope（TEM）and X-ray photoelectron spectroscopies（XPS）.Meanwhile,the prepared TiO₂ catalysts were applied in the oxidative desulfurization system（ODS）.Results showed that TiO₂ nanoparticles calcined at 500^oC（500-TiO₂）showed the best catalytic activity and the oxidation of DBT reached 99.8%with 0.04 g catalyst in 60 min while the n（O/S）is 4 at 50^oC.The sulfur removal of three different sulfur-containing substrates decreased in the following order:DBT>4-MDBT>4,6-DMDBT.Combined with TEM and XRD characterization,it was found that the activities of TiO₂ nanoparticles in the catalytic oxidation of DBT were positively correlated with the dispersions.Gas chromatography–mass spectrometer（GC-MS）measurements were employed to investigate the reaction mechanism,DBT sulfone（DBTO₂）was proved to be the only oxidation product of DBT after the reaction.By the electron spin resonance spectra（ESR）,·O₂^-radicals were proved to be the main active species in the oxidation process and a mechanism is proposed.2.a series of mesoporous core-shell TiO₂@SiO₂ catalysts were prepared via hydrothermal treatment combined with calcination.The composition and morphology of catalysts were analyzed by means of Fourier transform infrared spectroscopy（FT-IR）,wide angle X-ray diffraction,small angle X-ray diffraction,N₂adsorption-desorption,Scanning electron microscopy（SEM）,Transmission electron microscope（TEM）and X-ray photoelectron spectroscopy（XPS）.Meanwhile,the prepared TiO₂@SiO₂ catalysts were applied in the oxidative desulfurization system.Results showed that mesoporous 500-TiO₂@SiO₂ catalysts showed the best catalytic activity and could reach deep desulfurization under mild conditions.The recycling performance of the catalyst was investigated and after recycling for 6 times,the oxidation of DBT could still achieve a high removal of 99%.The sulfur removal of three different sulfur-containing substrates decreased in the following order:DBT>4-MDBT>4,6-DMDBT.Combined with BET and small angle XRD characterization,it was found that the activities of TiO₂@SiO₂ in the catalytic oxidation of DBT were positively correlated with the mesoporous structure.By the electron spin resonance spectra（ESR）,·O₂^-radicals were proved to be the main active species in the oxidation process,and a mechanism is proposed.3.a series of uniform dispersed TiO₂/GC catalysts were prepared via hydrothermal loading combined with calcination.The composition and morphology of catalysts were analyzed by means of Raman,wide angle X-ray diffraction,TEM,SEM,EDS-Mapping,XPS and TG-DSC.Meanwhile,the prepared TiO₂/GC catalysts were applied in the oxidative desulfurization system（ODS）.Results showed that uniform dispersed 10%-TiO₂/GC catalysts showed the best catalytic activity and the removal of DBT could reach 100%with 0.1 g catalyst in 60 min while the n（O/S）is 4at 50°C.After been recycled for 5 times,the sulfur removal of the as-prepared catalysts could still reach up to 99%.Combined with Raman and TEM characterization,it was found that the activities of TiO₂/GC in the catalytic oxidation of DBT were positively correlated with the dispersion of TiO₂ nanoparticles loading on the surface of graphite carbon.With the increase of TiO₂ nanoparticles,the more active sites generated and the performance of ODS was raised,when the loading of TiO₂ nanoparticles was over capacity,the TiO₂ nanoparticles became aggregate and caused the decrease of ODS performance.GC-MS measurements were employed to investigate the reaction mechanism.By ESR and Raman（before and after reaction）,·O₂^-radicals were proved to be the main active species in the oxidation process,and a mechanism is proposed.