货币金属团簇的结构、稳定性与反应活性

Structures,stabilities and gas phase reactions of noble metal clusters

团簇与气体分子的气相反应质谱技术是研究团簇稳定性和反应活性的主要手段,对比反应前后的质谱图横纵坐标变化,可以获得产物、团簇反应活性等信息;结合第一性原理计算,可以深入挖掘团簇、反应中间体、最终产物的结构,探究反应热力学、动力学过程,揭示团簇结构、稳定性与反应活性的内在关联。本文综述了Cu^(-)_(n)、Ag^(-)_(n)团簇与NO和O_(2)、O_(2)的气相反应质谱和第一性原理计算研究进展,阐述了具有独特稳定性的新奇开壳层超原子Cu^(-)_(18)、双闭壳层超原子Ag^(-)_(17)的稳定性来源,揭示了NO在Cu^(-)_(n)团簇上吸附的反馈与负反馈作用机制,O_(2)分别在Cu^(-)_(2n+1)、Cu^(-)_(2n+1)(或Ag^(-)_(2n))团簇上遵循双电子、单电子转移机制。其中,O_(2)在Cu^(-)_(n)上的电子转移机制由自旋守恒规则调控,将团簇和O_(2)分别类比于碱、酸溶液,根据不同碱性团簇跨越不同程度的自旋激发或解离势垒并于最后放出近乎相同热量的现象,提出O_(2)吸附与解离新机制自旋协同的拉平效应。能量分解-化学价态自然轨道数据显示,金属Cu^(-)_(n)团簇对NO和O_(2)的活性以及Ag^(-)_(n)团簇对O_(2)的活性皆受团簇的几何构型、电子结构、能量学数据调控。

Gas-phase reactions are reliable strategies to explore the stability and activity of metal clusters,which can provide the information of products and the cluster activities by comparing the changes of the X,Y-axis of the mass spectrum before and after the reaction.Combined with ab initio calculation,we can deeply explore the structure of clusters,reaction intermediates and final products,explore the reaction thermodynamics and kinetic process,and reveal the essence and relationship between cluster structure,stability and reaction activity.In this paper,by investigating the gas-phase reaction mass spectra of Cu^(-)_(n)clusters with NO and O_(2),Ag^(-)_(n)clusters with O_(2),and further combined with the ab initio calculation,novel open shell superatoms Cu^(-)_(18),double closed shell superatoms Ag^(-)_(17)with unique stability are reported.Besides,we demonstrated the donation and back donation interactions between NO and Cu^(-)_(n).Chemisorption of O_(2)on Cu^(-)_(2n+1),Cu^(-)_(2n+1)(or Ag^(-)_(2n))clusters follows the double and single electron transfer mechanism,respectively.Among them,the behavior of O_(2)on Cu^(-)_(n)is enabled by the spin conservation rule.By analogizing the cluster and O_(2)as base and acid respectively,we found a phenomenon that clusters with different alkalis pass through different degrees of spin excitation or dissociation barriers,and finally release almost the same heat for O_(2)dissociation.Based on this,a fully new mechanism of O_(2)on metal clusters was proposed:leveling effect of spin accommodation.Calculations of energy decomposition analysis-natural orbitals for chemical valence show that the activities of Cu^(-)_(n)clusters towards NO and O_(2),Ag^(-)_(n)clusters toward O_(2)are closely related to cluster geometry,electronic shell arrangement and energetics data.