Theoretical Studies On The Structures And Reaction Mechanisms Of Thorium Oxide Clusters With Water

Thorium oxides have important applications in refractory materials,ceramic materials,optical materials and industrial catalysts,and they are especially used as potential nuclear fuels due to the specific physicochemical properties of thorium oxides.In order to further explore the applications of thorium oxides,it is necessary to make a study on the geometrical configuration,electronic structure and reaction activity of thorium oxides clusters.In this dissertation,we report the theoretical studies on the structures and reaction mechanisms of thorium oxide clusters with water.A summary of the work is given as following:1.Density functional theory(DFT)calculations are employed to investigate the structural properties,electronic structures,chemical bonding and structural evolution of a series of thorium oxide clusters ThOn-/0(n=2-5).Generalized Koopmans'theorem is applied to predict the vertical detachment energies(VDEs)and simulate the photoelectron spectra(PES)of anionic ground states.The results show that oxygen radical,peroxide,and superoxide are found in the oxygen-rich clusters ThOn-/0(n = 3-5)which may be considered as the molecular models for O2 adsorption and CO oxidation,indicating that the oxygen-rich clusters have potential application prospects in catalysts.2.Theoretical calculations are performed to study the water splitting by thorium oxide clusters of varying size(ThO2)n(n = 1-3)and thorium oxide clusters with different charge ThO2-/+.According to the Energy profiles,there are similarities in the reaction mechanisms of thorium oxygen clusters with different sizes and different charge:The hydrogen transfer reactions to form the Th-H bond are followed by H-H recombination and H2 desorption from(ThO2)nO and ThO3-/+.Comparison the activation energies and driving forces for these reactions,the reactivity follow the order anionic>cationic>neutral thorium oxide clusters.3.Based on the theoretical study of thorium oxide clusters reacting with one water molecule,density functional theory calculations are carried out to investigate the reactions of thorium oxide clusters ThO2-/0/+ and ThMO4(M = Th,Ti)with several water molecules.Our calculated results show that the first two H2O molecules are dissociated on ThO2 forming Th(OH)4.From the third H2O molecule,the additional water molecules will be adsorbed on Th(OH)4 forming water clusters.All of the above reactions are barrierless and exothermic,and the released energies follow the order ThTiO4>ThO2,Th2O4,>ThO2+,ThO2-for thorium oxide clusters.This work can provide a theoretical reference for the design of water-splitting catalysts.