Theoretical Study On The Dynamic Catalytic Properties Of Metal Clusters

Metal clusters have been widely used in heterogeneous catalysis and their catalytic performance is closely related to their configurations and electronic properties.For catalytic reactions,the changes of the catalytic system during the catalysis process are relatively complicated,such as the interactions between small molecule adsorbates and the adsorption sites on the surface of the metal clusters,configuration changes of metal clusters and the effect of the charge of the charged clusters on the adsorbates.These are all aspects to be considered.At present,due to the limitation of the experimental technology,the catalytic behaviors and configuration changes of the clusters during the catalytic reactions cannot be directly observed through experiments.In this thesis,we used the method that combines density functional theory based molecular dynamics(DFTMD),free energy perturbation theory(FEP)and constrained molecular dynamics(Constrained MD)method to simulate the dynamic process of clusters during the catalytic reactions.This thesis simplified the model used in the theoretical simulation process,focusing on the effect of temperature on the electronic structure of the clusters and the dynamics changes of the cluster structures during the catalytic process.Firstly,this thesis mainly focused on the temperature dependence of the ionization potential and the electron affinity of gold clusters.The effect of temperature on electronic properties of gold clusters was analyzed by calculating the ionization potential and the electron affinity of the gold clusters at different temperatures.The reason for the temperature dependence of the redox potential was explained by relating to the caloric curves of the charged gold clusters and neutral gold clusters.Second,the model for studying the electronic properties of pure metal clusters was relatively simple,this thesis further built a more complex model system to study the catalytic behaviors of metal clusters during the catalytic reaction.The elementary reaction of nitrogen dissociation on ruthenium clusters was selected as the research object.Although understanding the nature of active sites on ruthenium cluster surface is crucial in catalyzing nitrogen dissociation,little is known about the relationship between cluster structure dynamics and elementary reactions.So the second work in this thesis focused on studying the relationship between the dynamic changes of cluster structures(i.e.the entropy changes of the catalytic system)and temperature during the reaction process,and explained temperature dependence of entropy changes by analyzing the melting behaviors of reactants,transition state and products.