Modulation Of Defects In Zr/Ti-MOFs And Application In Oxidative Desulfurization Of Dibenzothiophene

The sulfur compounds in petroleum-based fuel result in the emission of harmful SO_x gases after combustion.The SO_x gases can react with the atmospheric water vapor to form acid rain which brings severe damage to the environment.Thus,the sulfur content limits in the fuels,especially in gasoline and diesel are becoming increasingly stringent worldwide.To clean sulfur compounds from fuel,hydrodesulfurization（HDS）has been commonly used due to its high efficiency.However,it presents less effective at the removal of refractory sulfur compounds such as dibenzothiophene and its derivatives.For this,the oxidative desulfurization（ODS）,as one of the most promising processes has received considerable attention to remove these refractory sulfur compounds owing to its efficiency,low cost and mild reaction conditions.Recently Metal-organic frameworks（MOFs）have been considered as very promising heterogeneous catalysts owing to their large surface areas and high density of active sites as well as having highly tunable properties.The MOFs is commonly used as a support in catalysis,while few studies explore their intrinsic catalytic properties.This is because that the pristine MOFs is lack of catalytic active sites.To enable the applications of MOFs,numerous procedures have been explored to functionalize the MOFs in recent years.Among the procedures,defect engineering has been reported to be a promising approach.Generally,the Zr and Ti are very active for the ODS,so UiO-66 and Mi L-125 were selected in this work.The defective porous metal-organic framework UiO-66 and MiL-125 were prepared by simply tuning the synthesis time and replacement of terephthalic acid with the ligand benzoic acid,respectively.（1）Tuning the reaction time of ZrCl₄,BDC and NH₃?H2O in DMF at 110℃afforded a series of defective porous metal-organic framework UiO-66-t.XRD,SEM,Raman,N2-sopriton and TGA analysis reveal that rapid synthesis produces abundant defects and large pores in UiO-66.In the oxidative desulfurization,the rapid synthesized UiO-66 exhibit excellent activity,which is attributed to the abundant defects and large pores.The defects promote the formation of Zr-peroxo intermediate between the Zr⁴⁺and H₂O₂.And the large pores advance the diffusion of reactants,increasing the contacts between reactants and active sites.This work provides a simple and fast method for creation of defects in UiO-66.（2）Creation of defects endows many specific properties in MOFs..Herein,we try to synthesize defective Mi L-125 by replacing part of terephthalic acid with benzoic acid.XRD,N₂-soprtion and TGA analysis reveal that the concentration of defects in Mi L-125 is increasing with the increase of benzoic acid usage.Furthermore,the introduction of benzoic also creates mesopores in Mi L-125..Compared to the Mi L-125 prepared without using benzoic acid,the as-synthesized defective Mi L-125catalysts show better activities for the oxidation desulfurization,and the Mi L-125-15%exhibits the highest activity for the ODS.The defects facilitate the formation of Ti-peroxo intermediate between the Ti⁴⁺and H₂O₂,and the large pores advance the diffusion of reactants,both of which are benefit for the ODS.This suggests that creation of defects provides a route to improve the catalytic activities of MOFs for the ODS.