Theoretical Studies On The Structure And Reactivity Of Yttrium Oxide Clusters

Yttrium oxides have important applications in the fields of fireproofing,fluorescent reagent,electrode materials,magnetic materials,catalysts and so forth due to the unique physical and chemical properties of yttrium.In order to explore the internal relations among the electronic structure,chemical bonding and the relevant catalytic mechanisms,the related effective information needs to be achieved at the micro level.In the first step,we are interested in systematically studying the electronic structures,chemical bonding and structural evolution of isolated yttrium oxide clusters,and then the potential active sites of yttrium oxide clusters(including the doped yttrium oxide clusters)will be researched.A summary of the work is given as following:1.Density functional theory(DFT)and coupled cluster theory CCSD(T)calculations are employed to investigate the structural properties,electronic structures,chemical bonding and structural evolution of a series of tri-yttrium oxide clusters Y3Ox-/0(x = 0-6).The molecular orbital analyses and the photoelectron spectra(PES)are performed to analyze the chemical bonding in the tri-yttrium oxide clusters and elucidate their electronic and structural evolution.?-and ?-aromaticity is found in Y3-by molecular orbital analysis and Adaptive Natural Density Partitioning(AdNDP)analysis.As for the oxygen-rich clusters(Y3O6-and Y3O6),O22-and O2-· units are found,which can be viewed as the products that Y3O4-and Y3O4 interact with dioxygen,respectively.2.Theoretical calculations at the BP86 level are carried out to search the global minimums for the aluminum-doped yttrium oxide clusters Y2AlOx-/0(x=0-6).Generalized Koopmans' theorem is applied to predict the vertical detachment energies(VDEs)and simulate the photoelectron spectra(PES)of anionic ground states.The trends of first VDEs and electron affinities(EAs)for Y3Ox-/0 and Y2AlOx-/0(x=0-6)are analyzed.The results show that the trends of VDEs and EAs for Y3Ox-/0 and Y2AlOx-/0(x = 0-6)are nearly consistent.Because of the contribution of 2s and 2p of Al,the values of VDEs and EAs for Y2AlOx-/0(x=0-6)except for Y2AlO3-/0 all slightly increase compared with Y3Ox-/O(x=0-6),and the intrinsic reasons are analyzed through the molecular orbital analysis.3.Based on the studies of Y3Ox-/0 and Y2AlOx-/0(x = 0-6)clusters,the catalytic reactivity for CO/N2O using Y3O5 or Y2AIO5 as catalysts are studied,respectively.The potential energy surfaces are calculated to clarify the reaction mechanisms and manifest the doping effects.The terminal oxygen radical(O1·)plays an important role in the oxidizing reaction of carbon monoxide.Comparing with the reaction of Y3O5 oxidating CO,the reaction of Y2AlO5 with CO is direct and has no need to form the"prepared state" as CO has shaped on the Y site of Y3O5.The differences are produced by doping effects which may control the spin distributions and local charges in the oxidation of CO and the reduction of N2O,respectively.We have analyzed the differences by molecular electrostatic potential analysis,spin density analysis and natural bond orbital analysis in the current study.