Preparation Of Polyoxometalate Based Catalyst And Its Application In Extraction Oxidation Desulfurization Of Fuel

In recent years,with the rapid development of entity industrial and the improvement of modern living standard,the demand of fuel is picking up year by year.The extensive use of fuel not only brings convenience to people's production and life,but also causes a series of environmental problems,such as acid rain and haze.One of the main causes of environmental pollution is the release of a large number of acid gas(SO_X)and solid particles such as sulfate during the combustion of fuel.The emission of these harmful substances not only causes environment pollution,but also damages the respiratory tract and retina of organisms,especially human,and even threatens people's health.In order to control the pollution and damage caused by the combustion of sulfur-containing fuel,measures should be taken from the source of pollution.That is to say,deep desulfurization processing of fuel is very necessary.At the same time,different countries and regions in the world have also enacted strict restrictions on the content of sulfur in fuel(<10 ppm),which further makes the development of fuel desulfurization technology and balance the contradiction between environmental pollution and heavy use of fuel are imminent.Extraction-oxidation desulfurization technology is a new and efficient desulfurization method which combines extraction with oxidation technology.The extraction oxidation desulfurization technology overcomes the complicated operation of the traditional oxidation technology required oxidation first and then removal,and the poor effect of pure extraction desulfurization.One of the key points of this technology is the selection and preparation of high activity catalyst.Polyoxometalates(POMs)have been widely used in various catalytic oxidation reactions due to their unique acidity,strong oxidation property,"pseudo liquid phase"behavior,and easy design and regulation of structure and properties.POMS can be modified or loaded to improve its drawbacks,such as high dissolubility in polar solvent,low specific surface area and poor recyclability.Therefore,the preparation of high activity heterogeneous catalysts based on POMs is the focus of this thesis.The main contents of this paper are as follows:(1)The supported catalysts([C_nVP]MoV/CA)were obtained by loading the polyoxmetalate{[C_nVP]Mo V(n=2?4?6?8?10)}modified by pyridine cation substituents on the mesoporous carbon aerogel(CA)through one-pot method.The structure and morphology of catalysts were analyzed by various characterization methods,and the catalysts were applied to the removal of thiophene from simulated fuel.The experimental results show that the catalyst[C₆VP]Mo V/CA can remove 99.6%sulfide in the simulated fuel after 180 min under the optimal reaction conditions,with oxygen in the air as the oxidant.(2)Supported catalysts were prepared using poly imidazole-substituted polyoxometalates{P[Vim R]Mo V(R=Et?Pr?Bu?Am?He)}as active components and graphene oxide(GO)as support.The obtained materials were characterized,analyzed and applied in desulfurization test.With oxygen in the air as oxidant,the best catalyst P[Vim Am]Mo V/GO can remove 98.3%sulfide in the simulated fuel after 150 min reaction.(3)Monomer,dimer and polymeric cationic-substituted polyoxometalates were synthesized by ion exchange method.Then three kinds of catalysts([Vim]Mo V/GO,[DVim]Mo V/GO and P[Vim]Mo V/GO)were obtained by loading modified polyoxometalates on the surface of graphene oxide.The polyoxometalate(P[Vim]Mo V)modified by polymeric cationic has high catalytic activity,and the catalyst P[Vim]Mo V/GO can remove 99.7%sulfide from the fuel after 90 min with H₂O₂ as oxidant under the optimum reaction conditions.(4)Two kinds of peroxopolyoxometalates[(Bu₄N)₃PW₄ and(Bu₄N)₃PMo₄]were synthesized by ion exchange method using tetrabutylammonium chloride(Bu₄NCl)and phosphotungstic acid or phosphomolybdic acid as raw materials.The desulfurization efficiency can reach 99.7%within 40 min using(Bu₄N)₃PW₄ as catalyst and[Bmim]PF₆ as extractant.(5)The high activity supported catalyst PW₄@MIL-101 was prepared by encapsulating(Bu₄N)₃PW₄(PW₄)in the channel of MIL-101.Under the optimum conditions of(Bu₄N)₃PW₄,99.8%sulfide can be removed in 40 min catalyzed by PW₄@MIL-101.In addition,the catalytic system PW₄@MIL-101/[BMIM]PF₆ has better recyclability,and the catalyst has good reusability.(6)Three supported catalysts PMo₄@MIL-101,PMo₄@MOF-808 and PMo₄@ZIF-8 were prepared by encapsulating(Bu₄N)₃PMo₄(PMo₄)into the channel of MOF with different window sizes.The larger window size of MIL-101 is conducive to the reaction of sulfides with active components,which makes the catalyst PMo₄@MIL-101 have the best catalytic activity.The catalyst can remove 99.2%sulfur compounds in the multi-component simulated fuel,and the activity can still reach more than 99%after ten cycles.