The Construction Of Atomic Molecular Cluster In-situ Reactor And Reactivity Study Of Transition Metal Nitrogen/Oxide Clusters

Cluster plays an important role in bridging the atoms/molecules and condensed phase materials.The physical and chemical properties of condensed phase materials are constantly changing as the size increases.Compared to condensed phase materials,gas phase clusters,which have well defined composition and structure,can be treated by mass spectrum and quantum chemistry calculations to get accurate information.about the physics-chemical reactions.Gas phase clusters is an ideal model to probing intrinsic reaction mechanism.This dissertation focuses on the construction and application of instruments for cluster chemistry and the structures of transition metal oxide/nitride clusters and their reactivity.Chapter one is about the clusters of science,the introduction of experimental methods for cluster preparation,structural characterization,the reactions of clusters with small molecules,and quantum chemistry calculations.Chapter two introduces the set up work of atomic molecule cluster in situ reaction device.A reflectron time-of-flight mass spectrometer equipped with a laser ablation ion source,a quadrupole mass filter and a linear ion-trap reactor were used to achieve the quality of ion selection,trap reaction and abundance detection.Instrument principle,simulation design and application of building made a detailed introduction in this chapter.Third chapter introduces the reactivity of Fe_xO_y⁺(x=1-4,y=1-6)with linear alkanes n-C_nH_2n+2(n=3,5,7).In the reaction of Fe₂O⁺with C₃H₈,H₂ is liberated via C-H bond activation,with the formation of Fe₂OC₃H₆⁺.Furthermore,Fe₂O⁺cations can activate both C–H and C–C bonds of larger alkanes(n-C₅H₁₂ and n-C₇H₁₆),resulting in the generation of alkenes and lighter alkanes.Interestingly,when a mixture of C₃H₈/O₂was introduced into the reactor,an intense signal corresponding to Fe₂O₂⁺was present;the experiments indicate that the O–O bond in O₂ is efficiently activated over Fe₂O⁺and the newly formed C₃H₆ moiety is further oxidized to be C₃H₆O.This system includes the process by which iron oxide activates oxygen and hydrocarbons simultaneously and DFT calculations were also performed and the computational results are in good agreement with the experiments.Chapter four introduces the activation of alkane as mediated by the triatomic anion HMo N^-.HMo N^-can activate C-H bond of ethane,producing ethene and hydrogen molecules,and Zr NH^-is inert or reacts very slowly with C₂H₆.Compared to the previously reported HNb N^-,which is reactive toward CH₄.The molecular orbital analysis indicates the sd hybrid orbital of the metal atom in transition metal nitride is a pivotal factor for alkane activation by transition metal nitride ions,and the reactivity of ions can be changed efficiently by adjusting compositions of active orbitals.Compared another transition metal nitride system,the Ta₃N₂C₂^-cluster can activate one ethene molecule efficiently,the full dehydrogenation of the C₂H₄ molecule was observed,with the formation of two dihydrogen molecules.Interestingly,the two carbon atoms originating from the first C₂H₄ molecule are used to construct another cluster Ta₃N₂C₂^-,which can activate one more C₂H₄ releasing one H₂ molecule and all Ta atoms coordinate to Ta₃N₂C₄H₂^-.This may point the way to find approaches in tailoring the design of catalysts with controllable reactivity.