Study On Desulfurization Of Fuel Oil Catalyzed By Carbon Supported Polyoxometalates And Their Derivatives

Organic sulfur compounds in fuel oil are usually converted into sulfur oxides during combustion,resulting in various environmental and health problems.However,the production of ultra-low sulfur fuel is still a challenging problem.Oxidative desulfurization(ODS)is a feasible alternative method for deep desulfurization,and the development of new and efficient heterogeneous hybrid materials is the key to deep desulfurization.In this paper,POM was fixed on carbon coated silica gel material,and a variety of supported POMs hybrid materials were prepared by high-temperature calcination.The deep catalytic oxidation desulfurization was carried out in the system with H₂O₂as oxidant,and finally the possible catalytic oxidation desulfurization mechanism was explored.(1)A carbon coated silica gel hybrid material loaded with Keggin POMs was designed and prepared by multi-step method C@Si O₂-POM with micron silica gel as carrier?Firstly,N-vinyl imidazole(PVI)was grafted onto silica gel particles by graft polymerization.Then,POMs were combined with the carrier through electrostatic adsorption to obtain the composite PVI/Si O₂-POM.Finally,the composite was calcined at high temperature in air atmosphere to obtain the catalyst C@Si O₂-POM.The structure was characterized by SEM,FT-IR,XRD and XPS.Acetonitrile as extractant,H₂O₂as oxidant,the extraction oxidation desulfurization performance of fuel oil was studied with C@Si O₂-POM as catalyst.It is found that the desulfurization sequence of catalysts loaded with different POMs was as follows:C@Si O₂-Si W₁₂>C@Si O₂-PMo₁₂>C@Si O₂-PW₁₂.When the calcination temperature was400?,C@Si O₂-Si W₁₂-400 has the best desulfurization performance,which is mainly due to the formation of defective Si W₁₂in the catalyst,which is conducive to the activation of H₂O₂.Therefore,it shows good catalytic performance.(2)Crosslinked polyethylene imidazole(CPVI)modified silica gel loaded Si W₁₂precursor Si W₁₂-CPVI@Si O₂was prepared by one-step method,and then calcined at high temperature in air atmosphere to carbonize the CPVI,thus carbon coated silica gel particles loaded Si W₁₂were prepared.The structure was characterized by FT-IR,TEM,XPS and other characterization methods.Using H₂O₂as oxidant and acetonitrile as extractant,the desulfurization performance of Si W₁₂@C@Si O₂catalytic oxidation of simulated fuel containing DBT was studied,and the optimum process reaction conditions were explored.The results show that Si W₁₂on Si W₁₂-CPVI/Si O₂precursor exposed more active sites after calcination at 400?,so it has the best ODS efficiency.Acetonitrile as extractant,H₂O₂as oxidant Si W₁₂@C@Si O₂-400 as catalyst,DBT in simulated fuel can be completely removed within 20 min at 60?.There was no obvious loss of catalytic activity after 5 cycles of use.(3)Further,CPVI coated on silica gel was combined with metal pyridine porphyrin(MTPy P,M=Zn,Fe,Ni,Mn,Co,Cu)by axial coordination method.Then POMs were fixed on its surface by electrostatic adsorption to form POM-MTPy P-CPVI/Si O₂precursor loaded with POMs and metal pyridine porphyrin.The precursor material was annealed at high temperature in N₂atmosphere to obtain the final product Si O₂based carbon supported transition metal compound.The final product was characterized by XRD,SEM and XPS,and the catalytic oxidation desulfurization performance of the final product for model oil containing DBT was investigated.The results show that the type of POMs and the type of metal atom in the porphyrin center have a great influence on the oxidative desulfurization performance of the calcined products.The oxidation desulfurization effect of the final product annealed at 500?is the best,marked as Mo O₃-Zn@C@Si O₂-500.Its good catalytic activity was mainly due to the good catalytic oxidation of the active center Mo O₃and the adsorption of DBT by porous carbon on the surface of silica gel.When the amount of catalyst was 30 mg,the simulated fuel containing 500 ppm DBT at 60?can achieve complete desulfurization within 20 min.It can still maintain good catalytic oxidation desulfurization activity after being recycled for 7.