Atomistic insight into the properties of nanoporous gold using single crystalline model surfaces

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The rational design of npAu catalysts requires an atomistic understanding of the reaction mechanisms as well as their dependence on different parameters characterizing the system such as the presence of low coordinated sites, the concentration of a second metal component or the presence of an oxygen phase on the surface of the catalyst during oxidation reactions. Within this project we aim at investigating model surfaces to gain insight into the impact of low coordinated sites, the second metal component or the presence of additional reactions partners such as water on the catalytic properties of the system by measuring the micro kinetics of the surface reactions (analyzing the gas phase using mass spectrometry) and the surface species present under reaction conditions (in-situ IR spectroscopy) as a function of these parameters. Through the tight cooperation with the theoretical subprojects SP7 (Klüner) and SP8 (Moskaleva) as well as the gas phase catalysis project SP1 (Bäumer) we aim at a comprehensive atomistic picture of the observed reactivity. Within this project the partial oxidation of methanol and propene will be elucidated as prototypical reactions to test for the impact of the abovementioned parameters. The formation of the ester (methanol) and propylene oxide (propene) proceed via complex mechanisms characterized by a variety of parallel reactions paths, which renders selectivity a major issue. In such a case it is of particular importance to investigate the reaction isothermally using a defined concentration of educts to address the question of selectivity. Therefore, we employ molecular beams capable to provide a controllable flux of educts to impinge on the sample of a given temperature. Au(111) and Au(332) surface will be used as models to elucidate the impact of low coordinated sites on the reactivity of the systems. In a second step these surfaces will be modified by Ag and Cu. A particular focus will be on the role of water, which was shown in previous experiments to be able to significantly alter the reactivity of Au surfaces.To enable the direct comparison between the reactivity of the model system with that of np-Au it is planned to set up a high pressure cell attached to the ultrahigh vacuum system, which will allow to characterize the reactivity of the system at atmospheric pressure. This extension of the UHV apparatus will also enable to study np-Au samples under UHV conditions, which will allow compare the reactivity of both systems directly.