Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 15: Heterogeneous catalysis I

O 15.5: Talk

Monday, March 26, 2012, 17:00–17:15, MA 042

Chemical Waves and Rate Oscillations in the H2 + O2 Reaction on a Bimetallic Rh(111)/Ni Catalyst — •Tim Smolinsky¹, Florian Lovis¹, Andrea Locatelli², Miguel Niño^2,3, and Ronald Imbihl¹ — ¹Institut für Physikalische Chemie und Elektrochemie, Leibniz-Universität Hannover, Callinstr. 3-3a, D-30167 Hannover, Germany — ²Sincrotrone Trieste, S.C.p.A., S.S. 14, km 163.5 in Area Science Park, 34012 Basovizza, Trieste, Italy — ³Instituto Madrileño de Esudios Avanzados IMDEA Nanociencia, Cantoblanco 28049, Madrid, Spain

The H2 + O2 reaction on a Rh(111) surface alloyed with Ni was studied in the 10-6 - 10-4 mbar range using photoemission electron microscopy (PEEM), low energy electron microscopy (LEEM) and its spectroscopic variant (SPELEEM) as main analytical methods. The Rh(111)/Ni surface was prepared by decomposing Ni(CO)4 on the Rh(111) surface resulting in an alloy with about 25% Ni in the topmost layers. The original bistable system Rh(111)/O2 + H2 is transformed into an excitable system through the addition of Ni. Chemical wave patterns involving target patterns, pulse trains and rotating spirals can be observed. These spatiotemporal patterns were accompanied by rate oscillations observed with mass-spectrometry. Under reaction conditions three-dimensional NiO particles form on the surface ranging from less than 1 μm up to 50 μm in size. The size of these particles depends on the total pressure. A preliminarily excitation/oscillation mechanism is proposed based on the reversible segregation of Ni to the surface thus modifying the catalytic properties of the Rh/Ni surface.