Preparation And Oxidative Desulfurization Performance Of Zirconium And Titanium Based Metal Organic Porous Materials

Oxidative desulfurization(ODS)technique has been considered as one of the most promising non-hydrodesulfurization technologies because of no hydrogen consumption,and mild reaction condition.Therefore,the development of new efficient ODS heterogeneous catalysts has been a research hotspot in this field.Among them,the catalytic performance of Zr or Ti based metal organic framework(MOFs)materials such as UiO-66(Zr)and MIL-125(Ti)in ODS reactions has been widely studied.However,the results showed that such materials exhibited low activity in the ODS reactions.To address the problem,based on the research of UiO-66(Zr)and MIL-125(Ti),this dissertation was focused on the preparation of new metal organic porous materials with Zr or Ti as metal center,the evaluation of the ODS performance and the discussion of catalytic mechanism.To solvethe problem that the Zr sites in UiO-66(Zr)structure were not active in the ODS reactions,active titanium sites were introduced into the structure of UiO-66(Zr)by ion-exchange method.The results showed that the catalytic performance of UiO-66(Zr)was greatly enhanced by Ti ion-exchange in the ODS reaction of dibenzothiophene(DBT).This strategy is efficient not only for UiO-66(Zr)with rich defects(UiO-66(Zr)-D)but also for UiO-66(Zr)with high crystalline(Ti-UiO-66(Zr)-H).Accordingly,the ODS activities of the samples after Ti ion exchange(Ti-UiO-66(Zr)-H and Ti-UiO-66(Zr)-D)were 12 times and twice as their parent samples,respectively.At a reaction temperature of 60 ?,the removal content of DBT over Ti-UiO-66(Zr)-H and Ti-UiO-66(Zr)-D reached 91.3% and 98.2% after 120 min,respectively.Due to the lack of defect sites in the structure of UiO-66(Zr)prepared by solvothermal method,conventional UiO-66(Zr)exhibited low ODS activity.Here,UiO-66(Zr)with rich defect sites(UiO-66(Zr)-green)was successfully prepared without the addition of solvent.The number of missing linkers per Zr-O cluster in UiO-66(Zr)-green reached 2.16,which is nearly 40% higher than that in UiO-66(Zr)prepared by solvothermal method(UiO-66(Zr)-solvent).The catalytic results showed that UiO-66(Zr)-green exhibited enhanced catalytic activity in the ODS reaction of DBT compared with UiO-66(Zr)-solvent.At a reaction temperature of 60 ?,the removal of DBT in the model fuel completed over UiO-66(Zr)-green after 90 min.Further,under the same reaction temperaure and reaction time,the removal content of 4,6-dimethyldibenzthiophene(4,6-DMDBT)reached 99.2%.Considering that the functionalization of organic linkers in the structure of UiO-66(Zr)may change its ability to gain and loss electrons,and they may influence the catalytic performance of UiO-66(Zr).Herein,nitro-and amino-functionalized UiO-66(Zr)have successfully been prepared without the addition of solvent.Then,the effect of functional groups on the catalytic performance of UiO-66(Zr)was systematically investigated.It was found that nitro-functionalized UiO-66(Zr)(UiO-66(Zr)-NO2-green)exhibited much better catalytic performance than UiO-66(Zr)and amino-functionalized UiO-66(Zr)in ODS reaction of DBT.The removal content of DBT in model fuel over UiO-66(Zr)-NO2-green reached nearly 100% within 30 min at 60 ?.Under the same reaction temperature and time,the removal content 4,6-DMDBT was 99.8%.Such excellent catalytic performance are mainly attributed to the introduction of strong electron-withdrawing groups on the organic ligands in the structure of UiO-66(Zr)that reduce the electron density around Zr metal centers and thus improve its ODS performance.MOFs with Ti metal centers like MIL-125(Ti)was inactive in ODS reactions because most of Ti sites in their structure were coordination-saturated.Titanium terephthalate porous materials similar to amorphous structure were prepared by solvothermal method.Such materials displayed superior ODS performance mainly due to the existence of rich coordination-unsaturated Ti sites.The removal content of DBT in model fuel over the material reached nearly 100% within 20 min at 60 ?.Further,a new titanium terephthalate porous material(Ti-BDC-A)with nanometer particle size and more unsaturated Ti sites was prepared with the assistance of acetic acid.The catalytic results indicated that Ti-BDC-A exhibited extraordinary ODS activity for the removal of DBT at room temperature,moreover the strong ability of separating the sulfone product from the oil phase by adsorption has achieved with a total sulfur removal content of 117 mg S/g catalyst.