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Processus élémentaires associés à la réaction d’oxydation de CO à basses températures sur des catalyseurs à base de Palladium et d’Or supportés sur Al2O3 et SiO2

Abstract : The aim of this thesis is to use an experimental microkinetic approach to characterize elementary steps involved in the oxidation of CO by O2 over Pd and Au catalysts supported on Al2O3 and SiO2 and to identify those controlling the rate of the reaction. On 1.4% Pd/Al2O3, the evolution of the production of CO2 (RCO2(t)) by oxidation of the adsorbed CO species (2 linear L and 2 bridged B) was followed during successive formationoxidation cycles. An induction period is observed leading to a CO2 peak characterized by tm and RCO2m. The study of the impacts of different experimental parameters on tm and RCO2m such as the duration of a desorption before oxidation, the partial pressure of O2, the temperature and thepretreatment of the catalyst allows us to characterize the different surface elementary steps of thereaction. A kinetic model is proposed which is based on the oxidation of the B CO species by a weaklyadsorbed O species formed on Pd sites liberated by the desorption and the oxidation of the L COspecies. This model allows us to interpret the differences in the catalytic activity of the catalyst for theCO/O2 reaction according to the pretreatment procedure after reduction with H2 at 713 K: cooling thesolid in hydrogen permits obtaining a CO conversion of ��100% in excess O2 whereas a desorption at713 K provides CO conversions < 4%. These differences are ascribed to the reconstruction of thesurface of the Pd particles during the hydrogen desorption at 713 K. On Au/Al2O3 and Au/SiO2, the study concerns the first step of CO oxidation: the adsorption of CO. For a set of experimental conditions (Temperature and partial pressures), the adsorption of CO at 300 K leads to a progressive reconstruction of the Au particles modifying significantly the propertiesof the adsorbed species. The kinetic of this reconstruction is studied.
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Emmanuel Rozé. Processus élémentaires associés à la réaction d’oxydation de CO à basses températures sur des catalyseurs à base de Palladium et d’Or supportés sur Al2O3 et SiO2. Autre. Université Claude Bernard - Lyon I, 2010. Français. ⟨NNT : 2010LYO10290⟩. ⟨tel-00807672⟩

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