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Aromatisation du propane sur des catalyseurs bifonctionnels de type Ga-MFI : impact de la hiérarchisation de la zéolithe ZSM-5

Abstract : The mixing Ga2O3 with the H-ZSM-5 zeolite yields to the same catalytic performance in n-hexane cracking, cyclohexane dehydrogenation and propane aromatization than a bifunctional catalyst prepared by cationic exchange. The real catalyst appears upon hydrogen pretreatment in which gallium (Ga2O) suboxide that results from Ga2O3 reduction, reacts with the zeolite Brønsted sites to yield to gallium hydrides.The dehydrogenation reaction of alkanes involves a bifunctional catalytic site constituted of a Lewis site (Ga species) and basic site (an oxygen of the zeolite framework). The aluminosilicate catalysts loaded with Ga are more efficient than the gallosilicate catalysts, therefore extraframework gallium species is more active than the framework gallium species.The coke formed during the propane aromatization is very polyaromatic with more than fifteen benzenic rings, is very toxic. The creation of intracrystalline mesopores by alkaline treatment.preserves the acidic properties of the zeolite (number and strength of acidic sites). The mesopores allow limiting the hydrogen transfer reactions but is not very effective for impeding the growth of the coke, the presence of mesopores are even negative for the dehydrogenation reaction making inefficient the hierarchical bifunctional catalysts in propane aromatization; the kinetically limiting step for this reaction being dehydrogenation.
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Mira Raad. Aromatisation du propane sur des catalyseurs bifonctionnels de type Ga-MFI : impact de la hiérarchisation de la zéolithe ZSM-5. Matériaux. Université de Poitiers, 2017. Français. ⟨NNT : 2017POIT2298⟩. ⟨tel-01980882⟩

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