The Preparation Of Polyoxometalates Catalysts And Catalytic Oxidative Desulfurization

Along with the concept of green chemistry and the worse of environment,the environmental protection consciousness of people is more and more strong,the removal of sulfur in fuel has also caused the wide attention from society.Gasoline or diesel can be considered the most potential fuel for transportation,which is also the main contribution to sulfur pollution resulting in the smog,acid rain,corrosion,and eutrophication.In recent years,more than half cities in China witnessed the fog and haze,and many people suffered from the damage of pollutant air.In order to reduce the emission of sulfur oxides,more and more researchers focus on the desulfurization of sulfur-containing compounds.At present,the deep oxidative desulfurization with oxygen as oxidant is the most promising research method.Polyoxometalates（POMs）is a metal oxide cluster compounds combined byoxygen bridge,and containing transition elements（such as vanadium,molybdenum,tungsten and niobium,etc）with high valence.Because of their special solubility,acidity and redox property are widely used in catalysis,medicine,biomass and other fields of research.In the field of catalysis research,POMs is mostly applied in catalytic oxidation experiment as catalyst by O2 or H2O2,such as catalytic oxidation of starch and desulfurization.Therefore,in this thesis,we designed and synthesized POMs with strong redox oxidation,and applied in desulfurization with O2 as oxidant to explore the catalytic oxidation property.The main work is as follows:1.（NH₄）₅H₆PV₈Mo₄O₄₀（NPVMo）with catalytic redox property was synthesized and characterized by IR、XPS、SEM、31PNMR,and so on.NPVMo was evaluated in oxidation desulfurization of dibenzothiophene（DBT）,benzothiophene（BT）and 4,6-dimethyldibenzothiophene（4,6-DMDBT）in a model oil using O2 as an oxidant.By controlling the reaction conditions,sulfur contents in the model oil were decreased from 500 ppm to less than 1 ppm corresponding to DBT,BT and 4,6-DMDBT with almost 100% yield of sulfone,respectively.Meanwhile,thiophene（T）is one of the main sulfur species in gasoline,which is difficult to be oxidized in conventional oxidative processes and to be removed from fuels.Noteworthily,thiophene was oxidized efficiently at 97% conversion catalyzed by NPVMo and O2 as oxidant.Such high activity was attributed to the electron transfer（reaction mechanism）between NPVMo and DBT.Meanwhile,NPVMo acted as a heterogeneous and stable catalyst and could be recycled ten times with a slight decrease in activity in the model oil.More importance was that NPVMo was also available for deep desulfurization for FCC gasoline and diesel to obtain almost clear products with extremely lower sulfur content（2.29 and 9.43 ppm,respectively）without formation of by-products ofoxidation to loss their octane values.2.On the basis of POMs to form NPVMo/bi-CoPc with property of catalytic oxidation.The catalyst was characterized by IR、XRD、SEM and NMR to define the composition and structure and applied to the catalytic desulfurization.By controlling the reaction temperature,reaction time and amount of catalyst to ensure the best condition of reaction.The experimental results show that in aerobic oxidation desulfurization,using 12 mg catalyst can make 4,6-DMDBT and DBT to be oxidized completely with the conversion of 100% under100 oC,5 h.BT can be oxidized completely under the same conditions with 7 h.And thiophene can be oxidized with the conversion of 93.3% after 8 h oxidation treatment.Such high activity of NPVMo/bi-CoPc was attributed to the strong oxidizing property of V and the bond of π in bi-CoPc to accelerate the electron transfer between NPVMo and DBT,and shorten the reaction period.Meanwhile,NPVMo/bi-CoPc can be recycled to reuse without complicated treatment.