Activation Of Inert H-H And C-H Bonds By Dual Gold Atoms Doped In Metal Oxide Clusters

Gold catalysts have attracted much attention because of their excellent catalytic performance exhibited in many reactions.Owing to the complexity of the catalyst surface,the mechanistic details for the surface-catalyzed reaction are still far from clear.The study of the interactions between gas-phase clusters and small molecules by experiment combined with theoretical calculations can shed light on the understanding of the complicated mechanism of the catalytic processes on surfaces at molecular level,which is of great importance for the rational design of better performing catalysts.The studies in this dissertation are focused on the activation of inert H-H and C-H bonds by dual gold atoms in clusters.The summary is as follows:(1)Consecutive H2 Oxidation Mediated by Au2VO4+ ClustersThe reactions of mass-selected gold-vanadium heteronuclear oxide cluster cations Au2VO4+ and Au2VO3+ with H2 have been investigated by mass spectrometry in conjunction with density functional theory calculations.Consecutive H2 oxidation by Au2VO4+ to generate Au2VO3+ and subsequently Au2VO2+ is identified.With the regeneration of Au2VO4+ from Au2VO2+ + O2,a catalytic cycle for H2 oxidation by O2 mediated with Au2VO2?4+ is proposed.Theoretical calculation results indicate that the dissociation of molecular oxygen species into atomic oxygen species is crucial for consecutive H2 oxidation reactions.In the catalytic cycle,gold atoms not only act as an active site to split the H?H bond in collaboration with O2? ion,but also promote the reduction of the oxygen molecule by storing and releasing electrons.This study provides molecular-level insights into the elementary mechanism of the H2 catalytic oxidation on the surface.The detailed results are given in the third chapter of this dissertation.(2)Methane Activation Mediated by Dual Gold Atoms Doped in Aluminium Oxide Cluster Cation Au2Al2O3+The study of chemical reactions between gold-doped oxide clusters and methane can provide molecular level mechanisms to understand the activity of gold species supported on metal oxides.The role of single gold atom in methane activation has been identified,while the effect of two or more gold atoms is far from clear.By employing mass spectrometry and theoretical calculations,the reactivity of heteronuclear oxide clusters with dual gold atoms(Au2Al2O3+)toward methane was explored.Three major reaction products with the formation of CH3·,AuCH2,and Au were observed experimentally.Theoretical calculations indicate that Au2Al2O3+ contains two separate gold atoms and one oxygen?centered radical(O?·).Two types of mechanisms for methane activation are identified.The reaction initiated by the O?· site primarily generates the CH3· through hydrogen atom abstraction while the reaction starting from the gold site mainly contributes to the generation of AuCH2 and Au via the mechanism of Lewis acid-base pairs.It was revealed that the formation of gold dimer species driven by the aurophilic interaction plays an important role in the second C?H bond activation.The detailed results are given in the fourth chapter of this dissertation.