Synthesis Of Ti-MOF For Catalytic Oxidative Desulfurization

With the increasing demand for energy,the utilization of fuel oil is also increasing proportionally.The massive combustion of fuel oil leads to the emission of sulfur compounds into the atmosphere.These sulfur compounds become one of the biggest threats to the environment.Therefore,the deep desulfurization of fuel oil has become a hot spot of environmental protection research.MOFs is a kind of periodic crystalline porous material composed of metal ions and organic ligands.Among them,MIL-125(Ti)is a titanium based MOF material with titanium oxide octamer as the active center.Because of its high specific surface area,adjustable morphology and pore size,and highly dispersed Ti metal,its research in catalysis has been widely concerned.However,the research on controllable synthesis and catalytic oxidation desulfurization of MIL-125(Ti)has not been reported.In this paper,MIL-125(Ti)crystal was synthesized by hydrothermal method.Firstly,the influence of solvent ratio and other synthesis conditions on the growth of MIL-125(Ti)crystal was investigated.Then the effect of acid addition on the morphology of MIL-125(Ti)crystal was investigated and its catalytic performance was studied.On this basis,calcination of the catalyst at different temperatures can regulate the pore structure.The structure and properties of the prepared catalyst were analyzed by various characterization.It mainly includes two aspects:(1)MIL-125(Ti)catalyst was modified by acid.The particle size of MIL-125-n%(n=0,5,10,15)crystal modified by acid decreased first and then increased with the increase of HAc addition,and the specific surface area increased first and then decreased with the increase of HAc addition.Under the same reaction conditions,MIL-125-n%series catalysts showed a trend of increasing DBT removal efficiency and then decreasing DBT removal efficiency in the simulated oil.It was found that the oxidation desulfurization rate constant of the catalysts had a positive correlation with the specific surface area.The desulfurization activity of MIL-125-10%catalyst is the highest,and the oxidation desulfurization reaction conditions of MIL-125-10%catalyst are optimized.In this catalytic oxidation desulfurization system,the valence state of Ti remains the same as+4,the active oxygen radical·O2-forms an active intermediate with Ti(?)as the active center of the catalyst,oxidizes the DBT extracted to the methanol phase to the corresponding sulfone(DBTO2)material,and achieves the effect of deep desulfurization.(2)The MIL-125(Ti)catalyst was calcined at different temperatures.The pore structure of”quasi-MOF" MIL-125-X(X=200,300,350,400)material was transformed from micropore to mesopore by calcining MIL-125(Ti)catalyst at different temperatures.Compared with MIL-125(Ti)catalyst,MIL-125-300 has three times higher DBT removal rate under the same conditions,because the mesoporous structure of MIL-125-300 catalyst has mesopores with size of 22 A-30 A,which is enough to make DBT enter into the pores and contact more active centers.In addition,MIL-125-300 shows high efficiency in selective oxidation desulfurization,and the main reason for MIL-125-300's high efficiency in selective oxidation desulfurization is the formation of Ti-?1-OOH configuration.