DFT Calculation Study Of Transition Metal Substituted Tungsten-polyoxometalate Activated Hydrogen Peroxide And Oxygen Molecules

Polyoxometalates(POMs)are a class of multinuclear complexes and It has been widely used in many fields.Because of its high catalytic activity and good selectivity,polyoxometalates have excellent application prospects on the reverse side of catalytic oxidation.With the effective combination and rapid development of quantum chemistry and modern computing technology,it has greatly promoted the application of quantum chemical theoretical calculation in the field of chemical science.In recent years,quantum chemical theoretical calculation has been widely used in the field of polyoxometalates chemistry as an advanced research method.In particular,it plays an important role in exploring the reactivity of polyoxometalates compounds and its catalytic oxidation reaction mechanism.In this paper,the density functional theory(DFT)method is used to calculate and study the reaction mechanism of H2O2 and O2 molecules activated by transition metal substituted Phosphotungstates.The research work mainly includes the following three aspects:(1)The DFT method was used to calculate the mechanism of activation of hydrogen peroxide(H2O2)by a divanadium-substituted polyoxometalate(POM)[?-PV2W10O38(?-OH)2]3-.The results show that coordination of H2O2 to[?-PV2W10O38(?-OH)2]3-occurs through a vanadium-center-assisted proton transfer pathway.The final species with catalytic activity produced by the reaction is[?-PV2W10O38(?-?2,?2-O2)]3-.Activation of H2O2 along the optimal reaction path involves two dehydration reactions.The first water molecule is removed during the reaction and the intermediate[?-PV2W10O38(?-OH)(?-OOH)]3-is formed.Subsequently,the second water molecule was removed through three successive water-assisted proton transfer pathways,eventually forming[?-PV2W10O38(?-?2,?2-O2)]3-.A detailed comparison of molecular geometry and electronic structure shows that the catalytic active species has very unique structural characteristics.(2)The DFT method was used to study the osmium tetroxide(OsO4)anchored on a silanol-functionalized polyoxometalate(POMs)to form an Os-POM catalyst,and O2 molecules were used as oxidants to catalyze the epoxidation of propylene.The results show that the rotation of the PO43-unit in the center of the POM causes the coordination environment of the transition metal Os center to change from a tetrahedron to a trigonal bipyramid.And this trigonal bipyramid structure has orbital energy levels that match the epoxidation of propylene,and the free energy profiles of the epoxidation of propylene is calculated.During the oxygen transfer process,the ?*anti-bond orbital of Os-POM accepts electrons from the ?-bonding orbital of propylene,thereby breaking the Os=O bond.The decomposition of O2 on the Os-POMcatalyst is a barrier free process.The ability of the POM platform to receive and stabilize excess electrons from the Os center effectively promotes the oxygen transfer process and facilitates the epoxidation of propylene by O2.(3)The DFT method was used to study the reaction of propylene epoxidation with Ferrate(FeO42-)anchored on POM to form Fe-POM catalyst,and H2O2 was used as oxidant.The results show that Fe-POM can be regarded as a high-valent Fe=O species,In chemical and biomimetic studies,it has proven to be a highly reactive intermediate for the oxidation of organic substrates by heme and non-heme enzymes and their model compounds.The combination of propylene with Fe-POM catalyst results in a cation radical species.Due to the high reactivity of radical,the activation energy barrier for propylene epoxidation is only 4.50 kcal/mol.Subsequently,H2O2 was decomposed into one H2O molecule and one surface O species on the Fe-POM catalyst,so that the Fe-POM catalyst was recovered.The Fe center acts as an electron acceptor in the first half of the reaction to accept electrons from the bound propylene molecules to form free radicals.