Thermal and Photon Stimulated Reactions on Metal Particles

University dissertation from Chalmers University of Technology

Abstract: The interaction between molecules and solid surfaces influence our daily lives in many ways. One important example is heterogeneous catalysis where surface reactions, for example, are used for production of chemicals and exhaust after-treatment. As surface reactions are complex, various different approaches are needed to explore the fundamental processes. One route is to study reactions at well-defined single crystal surfaces under ultra-high vacuum (UHV) conditions. However, as the reaction pathways may depend on pressure, ideally we would like to track how and if the interactions change with pressure. Furthermore, technical catalysts generally consist of nanometre-sized particles supported by an oxide material. This introduces the complexity of particle size-dependence, as well as effects arising from interactions between the reactants and the support material. The studies in this thesis range from fundamental studies in UHV to experiments under ambient conditions. Structure-wise, the studies encompass single crystal substrates and model catalysts. Furthermore, surface processes are stimulated by both thermal and photon energy. The fundamental aspects of thermally driven interactions of NO and water with sodium supported on a single crystal C(0001) surface were studied in UHV. Moreover, the influence of silver particle size (and to some extent shape) on the efficiency of photon driven desorption of NO from the Ag/C(0001) system was explored. Model catalysts were studied under ambient conditions by use of indirect nanoplasmonic sensing (INPS). In particular, INPS was used to determine the apparent activation energy for hydrogen oxidation as a function of platinum nanoparticle size, and to track the sintering of platinum clusters.

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