The Study Of The Reactions Between Gold-containing Heteronuclear Metal Oxide Clusters And Small Molecules

Gold catalysts have been shown to exhibit exceptional catalytic activity in many important chemical reactions. Because of the complexity of catalyst surfaces, the detailed mechanisms for surface-catalyzed reactions are still far from clear. The study of reactions of gas phase clusters with small molecules by experiments combined with theoretical calculations can help people to understand the surface reaction mechanisms at the 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 C-H、O-O and C-O bonds by gold in clusters. The summary is as follows:（1） Thermal Conversion of Methane to Formaldehyde Promoted by Gold in Au NbO₃⁺ cluster cationsThe reactions of Au NbO₃⁺ cluster cations with CH₄ and CD₄ have been investigated. In addition to generation of methyl radicals, a new reaction channel generating the stable organic molecule formaldehyde has been identified. The gold atom is a spectator in CH₃ formation but a very important player during HCHO formation. The gold atom stores negative charge released during oxidation of CH₄ to HCHO, and the conversion of an Au-O bond to an Au-Nb bond promotes the reaction. The Au NbO₃⁺ cluster is the first example of a heteronuclear oxide cation that can oxidize CH₄ to HCHO. This study further emphasizes that the interchange of Au-O and Au-M bonds can be an important process for oxide-supported gold catalysts. The detailed results are given in the second chapter of this dissertation.（2） CO Oxidation Promoted by Gold Dimer in ClustersInvestigations on the reactivity of atomic clusters have permitted the identification of the elementary steps involved with catalytic CO oxidation, a prototypical reaction in heterogeneous catalysis. The atomic oxygen species O?- and O^2- bonded with early transition metal（ETM） oxide clusters have been shown to be oxidative to CO. This study reports that when an Au₂ dimer is incorporated within the cluster, the molecular oxygen species O22-bonded to vanadium can be activated to oxidize CO under thermal collision conditions. The gold dimer was doped in Au₂VO₄^- cluster anions which reacted with CO in an ion trap reactor to produce Au₂VO₃^- and then Au₂VO₂^-. The dynamic nature of gold in terms of electron storage and release promotes CO oxidation and the O-O bond reduction. The CO oxidation on atomic clusters of this study parallels similar behaviors of CO oxidation on supported gold catalysts. The detailed results are given in the third chapter of this dissertation.