Polyoxometalate-based Metal-Organic Frameworks And Their Catalytic Oxidative Desulfurization Performance

Nowadays,people are concerned about the environmental pollution caused by the combustion of sulfur compounds in crude oils.In order to reduce the concentration of sulfur componds,researchers have been developing solutions,such as hydrodesulfurization(HDS),adsorption desulfurization(ADS)and catalytic oxidation desulfurization(ODS).Among them,the ODS method is considered to be the most effective,low-cost and mild method.Polyoxometalates(POMs),which are classified into heteropolyacids and isopolyacids,are composed of a class of high valance states transition metal atoms(eg.molybdenum,tungsten,rhenium,ruthenium,etc.)which coordinated to oxygen atom.Because POMs have good solubility,redox and acidity,hence they can be widely used in the fields of catalysis,medical detection and biomass conversion.And the POMs are used as inorganic linkers together with organic ligand which coordinated with metal ions to form a multifunctional POM-based metal organic materials by hydrothermal synthesis.This paper is mainly based on POM-MOF,evaluating the catalytic activity of the 2D POM-MOF,POM-MOF nanosheets and 3D POM-MOF as heterogeneous catalysts in ODS.1 We selected a two-dimensional layered POM-MOF material{[Co2(H20)4(BTX)3][PMo12O40],BTX=1,4-Bis(1,2,4-triazol-l-ylmethyl)benzene}.Considering that the hydrogen bond between the layers of two-dimensional MOF material,we used wet-ball milling and liquid-phase ultrasonic assisted methods to destroy the hydrogen bonds.The TEM and AFM characterization results proved that the ultra-thin POM-MOF nanosheets were obtained successfully.The exfoiated nanosheets had more active sites and fewer mass transfer limits,which can greatly increase the reaction rate.By monitoring the desulfurization process,the desulfurization efficiency of the nanosheet catalyst were 14 times higher than that of the bulk POM-MOF(TON of nanosheets and bulk POM-MOF was about 400 and 29,respectively).2 A novel three-dimensional amphiphilic POM-based MOFs[Zn(BTX)(Mo8O26)][TBA]2(denoted as POM-Zn-MOF)crystals were synthesized by solvothermal method and its composition and structure were characterized by Single-Crystal X-ray diffraction(SCXRD),powder XRD,IR and TG.POM-Zn-MOF material was used as a heterogeneous catalyst in the catalytic oxidation desulfurization experiment.The conversion rate of the reactants quickly reached 100%within 30 min(TON was about 24),and the catalytic performance was not reduced after recycling experiment.Based on the experimental results above,the amphiphilic POM-Zn-MOF had the advantages of high catalytic efficiency,stability and recyclability as heterogeneous catalyst,which was of great significance for the practical application of catalytic oxidative desulfurization.