Styrolsynthese an Eisenoxid-Katalysatoren: Vom einkristallinen Modellsystem im Ultrahochvakuum zum Realkatalysator im technischen Reaktor

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The project aims at developing a methodology for the unravelling of reaction mechanisms over metal oxide catalysts and the transfer of these insights from fundamental surface science studies on model systems under UHV conditions to the polycrystalline catalysts under technical process conditions. The example system under investigation is the dehydrogenation of ethylbenzene to styrene over unpromoted or K-promoted iron oxide. After the insights gained during the first grant period, more specific aims can be formulated for the second period: - The rate limiting step was identified to be the hydrogen abstraction from the adsorbed ethylbenzene molecule and not - as initially thought - product desorption. Hence, elaborate functional and kinetic models are needed for a proper description of the surface reactions. - Monocrystalline model catalysts and polycrystalline powder catalysts of the same composition feature analogue properties regarding their catalytic behaviour. A "materials gap" exists in the sense that under reaction conditions the oxide surface is covered by a dense carbonaceous layer which is relevant for the surface reactions. Therefore, it is necessary to reproducibly synthesise the respective top layer, to characterise it by means of surface science techniques and to theoretically determine stability conditions for its existence. During the second grant period we will concentrate on the unpromoted FexOy system under oxidative and nonoxidative conditions. We will revise and refine the functional models developed during the first grant period and derive consistent kinetic models. The kinetic parameters will be determined either directly from measurements over monocrystalline samples or from theoretical considerations based on molecular and quantum-chemical models. The model will be verified through experiments under quasi-technical conditions and will be employed for exploratory studies concerning the optimisation of the technical process. At a later stage we will consider the K promoted system as a practically relevant test case for the developed systematics.