Mechanism Study Of Catalytic CO Oxidation By Noble Atom Doped In Neutral Heteronuclear Oxide Clusters

Noble metal catalysts have attracted extensive attention because of their excellent catalytic performance in CO oxidation.It is technically difficult to uncover the mechanistic details of the reaction process by traditional experiment methods due to the complexity of related catalytic surfaces.Gas-phase clusters can be considered as the intermediate matter to bridge isolated atoms and the bulk catalysts,and have been proposed as the ideal model to understand the reaction mechanism at strictly molecular level.The study of neutral clusters serves as an important model to simulate the structure and reactivity of uncharged active sites on catalytic surface,which may provide essential information to modify and design catalysts rationally.The work in this dissertation focuses on the CO oxidation by the noble metal atom doped in neutral heteronuclear oxide cluster.The main contents are as follows:?1?The experimental and theoretical study of CO oxidation catalyzed by neutral gold-vanadium oxide clustersOxidation of CO by gas-phase atomic clusters is being actively studied to understand the molecular-level mechanisms of heterogeneous CO oxidation over related catalytic surfaces.However,it is experimentally challenging to study CO oxidation by neutral heteronuclear metal oxide clusters because of the difficulty of cluster ionization and detection without fragmentation.Herein,the reactivity of the neutral Au VO_2-4 clusters with CO and O₂ was studied by time-of-flight mass spectrometry coupled with single photon ionization technique.The experimental results showed that CO adsorption is the dominant channel on the interactions of Au VO₄ and Au VO₃ with CO,and Au VO₂ can pick up an O₂molecule to generate Au VO₄.Theoretical studies indicated that the oxidation of the trapped CO in Au VO_3,4CO into CO₂ is exothermic while the reaction barriers have to be overcome at the elevated temperatures.A catalytic cycle for CO oxidation by Au VO_2-4 is proposed.?2?The experimental and theoretical study of CO oxidation catalyzed by the neutral cluster Ir Al₂O₈ with iridium in a high oxidation state of?Metals with high oxidation states?HOSs??e.g.,+??+??are of great interest to chemists,while it is challenging to trigger the reactivity of metals with HOSs because they are usually highly-coordinated by anionic ligands to block the approach of reactants.Herein,we reported that neutral iridium-aluminium oxide cluster Ir Al₂O₈ can catalytically oxidize four CO molecules.The reactivity of iridium with nearly+?OS in Ir Al₂O₈ was successfully identified.Note that the exposed metal site toward reactants with OS lower than+?in a heteronuclear metal oxide cluster was commonly observed to drive the catalytic oxidation.In this work,new insights into the unique reaction pattern of the embedded Ir^?+that is not accessible for CO for the initial oxidation were provided.The key to trigger the reactivity of Ir Al₂O₈ in catalytic CO oxidation lies in the presence of a highly reactive atomic oxygen radical(O^·-).Crucial roles of coordinated lattice oxygen atoms(O^2–)around Ir^?+to modify the steric and electronic structure of Ir during CO oxidation were highlighted.