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MO: Molekülphysik

MO 3: Reactive and Energy Transfer Processes

MO 3.6: Vortrag

Montag, 2. April 2001, 17:00–17:15, H1058

Reaction mechanism for the oxidation of free silver dimers — •Jan Hagen¹, Liana D. Socaciu¹, Ueli Heiz², Thorsten M. Bernhardt¹, Thomas Leisner¹, and Ludger Wöste¹ — ¹Freie Universität Berlin, Institut für Experimentalphysik, Arnimallee 14, D-14195 Berlin, Germany — ²Ecole Polytechnique Federale de Lausanne, Institut de Physique Experimentale, CH-1015 Lausanne, Switzerland

Small dispersed silver particles exhibit unique properties in the heterogeneous catalysis such as the epoxidation of ethylene to ethylene oxide and the partial oxidation of methanol to formaldehyde. Since it was shown that silver has the ability to activate O₂ in these reactions it is important to investigate the chemical properties of silver. We study the kinetics of the interaction of Ag₂⁺ with O₂ in the gas phase under multi-collision conditions at various temperatures. A new experimental scheme is employed, which consists of an octopole ion trap of variable temperature inserted into a tandem quadrupole mass spectrometer. From the time evolution of the reactant and product molecule concentrations at different temperatures the corresponding reaction mechanism is extracted. Surprisingly, the product Ag₂O⁺ is detected, which is formed after molecular adsorption and dissociation of O₂. We can clearly identify Ag₂O₂⁺ as an intermediate in this reaction. In addition, absolute rate coefficients and activation energies for the molecular adsorption of O₂ onto Ag₂⁺ are presented.