Synthesis And Oxidative Desulfurization Performance Of Titanium And Vanadium Metal-organic Frameworks Based Materials

The sulfur-containing compounds in fuel oil would combust into SO_x and result in environmental pollution.To reduce pollution,the sulfur content in fuel oil must be reduced below 10 ppm in many countries according to the stringent demand of the environmental regulations.Oxidative desulfurization?ODS?has received much attention because it can be carried out under mild conditions and it is effective to remove the aromatic sulfur-containing compounds like dibenzothiophene?DBT?and4,6-dimethyldibenzothiophene?4,6-DMDBT?that are difficult to be desulfurized by industrial hydrodesulfurization?HDS?technique.Metal-organic frameworks?MOFs?as heterogeneous ODS catalysts have been studied due to the advantages of high surface area with tunable pore size and functionality.However,the research results indicate that generally they are not active because of the lack of active sites in their intrinsic structures.To solve the problem,the research interest of this thesis focused on developing MOFs catalysts with rich active sites for ODS reactions.The main contents are as follows:Firstly,the composite materials of amorphous TiO₂ and MIL-101?Cr?were prepared by impregnation method using tetrabutyl orthotitanate?TBOT?as Ti precursor.MIL-101?Cr?is helpful for improving the dispersion of amorphous titania and the number of exposed titanium active sites due to its high surface area and pore volume.As a result,MIL-101?Cr?/TiO₂ composites showed excellent reactivity in the ODS reaction of DBT.Moreover,by optimizing the addition amount of MIL-101?Cr?,a composite material with 10%MIL-101?Cr??10%MIL-101?Cr?/TiO₂?exhibited best catalytic activity.By using cumene hydroperoxide?CHP?as oxidant,99%DBT could be removed in 20 min at 60?.Meantime,the sulfur content in model oil decreased from 1000 ppm to less than 10 ppm.The reaction rate constant of 10%MIL-101?Cr?/TiO₂ was seven times as that of amouphous TiO₂.Secondly,to solve the problem that the catalytic activity per Ti site in MIL-101?Cr?/TiO₂ composite is relatively low,Ti-modified MIL-101?Cr?-NH₂-SF was prepared by Lewis acid-base interaction.Here,TBOT or TiCl₄ was chosen as Lewis acid and MIL-101?Cr?-NH₂-SF was used as Lewis base.At the beginning,an amino-functionalized MIL-101?Cr?with high surface area?MIL-101?Cr?-NH₂-SF?was successfully prepared by the amination of nitro-functionalized MIL-101?Cr?sythesized under solvent-free?SF?condition.Then,Ti-modified MIL-101?Cr?-NH₂-SF was obtained by the interaction between TBOT or TiCl₄ and MIL-101?Cr?-NH₂-SF.The results indicated that active Ti species could be grafted on the surface of MIL-101?Cr?-NH₂-SF and thus improve turnover number?TON?.The TON value of Ti-modified MIL-101?Cr?-NH₂-SF was twelve times as that of 10%MIL-101?Cr?/TiO₂.Finally,considering the feasibility and applicability of aerobic ODS system,catalytic acitivies of some representative MOFs under ambient air atmosphere were explored.It is shown that vanadium-containing catalysts were more active than titanium-containing catalysts when using air as oxidants.Thus,in this work,MFM-300?V?with V metal centers,was chosen as aerobic ODS catalyst.It was found that the DBT removal content over MFM-300?V?could reach 99.6%in 5 h at120?under ambient air atmosphere.Moreover,MFM-300?V?also showed good catalytic performance in the ODS reaction of 4,6-DMDBT.The removal content was98.1%in a reaction time of 6 h at 120?,suggesting that it had potential application in deep oxidative desulfurization.MFM-300?V?was active not only in hydrogen donating solvents but also in non-hydrogen donating solvents.Since non-hydrogen donating solvents were much close to the composition of real fuel oil,MFM-300?V?was promising in industrial application.In addition,MFM-300?V?can almost maintain the initial ODS performance after seven cycles,indicating that it had good structural stability and reusability during the ODS process.