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Interactions entre morphologies, acidités et diffusion dans les zéolithes beta : éléments de réponse par spectroscopie infrarouge, réactions modèles et chromatographie à flux inversés

Abstract : In order to study the impact of the size and morphology of zeolite crystals on the textural, chemical and diffusion properties, a series of beta zeolites was studied.The logical increase of the porous surfaces and volumes with the decrease in crystal size is observed. In addition, this also implies a decrease in the overall acidity as well as strength of the adsorption sites. However, understanding the complex acidity of these materials requires advanced characterization techniques.The adsorption of probe molecules (pyridine, CO, ethylene) followed by infrared as well as ammonia thermodesorption were correlated to model reactions of ethanol conversion and n-hexane cracking. In this case, the morphology of the crystals has little influence and performance is mainly dictated by the Brønsted sites. The presence of extra-framework aluminums makes it possible to exalt the acid strength of the protonic sites. With the transformation of ethanol, better activities and stabilities are observed in the case of hierarchical zeolites.The study of diffusion by the reversed-flow gas chromatography (RF-IGC) showed that if the diffusion coefficients increase as opposed to crystal size, the secondary porosity reduces the diffusion path. Moreover, the weak sites predominantly present on the hierarchized materials facilitate the desorption of the molecules and are involved in the lateral interactions measured by RF-IGC.This work thus provides elements of response to the stability and the complex catalytic behaviors observed on the beta zeolite.
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Submitted on : Monday, January 14, 2019 - 4:49:37 PM
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Mohammed Amine Benghalem. Interactions entre morphologies, acidités et diffusion dans les zéolithes beta : éléments de réponse par spectroscopie infrarouge, réactions modèles et chromatographie à flux inversés. Cristallographie. Université de Poitiers, 2017. Français. ⟨NNT : 2017POIT2295⟩. ⟨tel-01980831⟩

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