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No. of bitstreams: 1 DissILM.pdf: 5724691 bytes, checksum: 47011a82c00569e1418ba50a076d335c (MD5) Previous issue date: 2016-02-15 / Não recebi financiamento / Nanosized NaX zeolites (FAU) (crystallite size = 16 nm; Si/Al ratio = 1,5) were synthesized and modified through ion exchange with linear alkylammonium cations containing from one to six carbons, with the intent to activate basic sites. In this work, commercial microsized zeolites (Aldrich) were also ion exchanged for comparison matters and all samples were characterized. Scanning electron microscopy analysis showed that both micro- and nanosized zeolites containing sodium portray polycrystalline particles: the former presents octahedral habit and particle size of 2952 nm and the latter presents an indefinite habit and particle size of 426 nm. Among the ion exchanged samples, none presented complete exchange of the Na+ cations due to steric hindrance. Nanosized zeolites presented higher exchange degrees than the microsized ones, which is due to higher accessibility to the exchange sites. Such factors also explain the exchange degrees’ reduction with the cations’ chain length, which is less abrupt among the nanosized samples. This happens due to the nanosized samples’ higher interparticular porosity, which has also allowed their micropore volumes’ constant decrease, differently from the microsized samples, which faced a minimum value with butylammonium. When the cations’ length is increased, the unit cell expands in comparison to the zeolites containing sodium since bulkier cations cause variations in the length and angle of the of the O-Si-O and O-Al-O bonds. Through thermogravimetric analysis in oxidant atmosphere, it was observed that the longer the carbon chain length, the lower is the mass loss, which evidences the lower diffusional limitations. The same was observed in inert atmosphere, which indicates that the presence of O2 does not influence the thermal events. Nanosized zeolites illustrate smoother mass loss profiles, which marks smaller diffusional limitations. The zeolitic materials were catalytically evaluated along the Knoevenagel condensation between butyraldehyde and ethyl cyanoacetate (3% m/m catalyst) during 1 h. The nanometric zeolites presented higher conversions and higher reaction rates when t = 0 than the microcrystalline ones, confirming the advantages of nanosized materials. / Zeólitas NaX (FAU) de cristais nanométricos (diâmetro de cristalito de 16 nm; razão molar Si/Al de 1,5) foram sintetizadas e modificadas através de troca iônica com cátions alquilamônio lineares de um a seis carbonos para a ativação de sítios básicos. No trabalho, efetuou-se também a troca iônica com zeólitas de cristais micrométricos (Aldrich) para fins de comparação, caracterizando-se todas as amostras. Por MEV, observou-se que as zeólitas sódicas micro- e nanométricas possuem partículas policristalinas, apresentando as primeiras hábito octaédrico e diâmetro de partícula de 2952 nm e, as últimas, hábito indefinido e diâmetro de 426 nm. Dentre as zeólitas trocadas, nenhuma apresentou troca completa dos cátions Na+ devido a impedimentos estéricos. As zeólitas nanométricas apresentaram graus de troca superiores aos das micrométricas devido à maior acessibilidade aos sítios de troca. Tais fatores também justificam a redução do grau de troca com o aumento do comprimento do cátion de compensação, sendo essa redução muito mais suave entre as amostras nanométricas. Isto ocorre devido à maior porosidade interparticular das zeólitas nanométricas, a qual permitiu que os volumes de microporos dessas zeólitas fossem sempre decrescentes, diferentemente das amostras micrométricas que atingiram um valor mínimo com o cátion butilamônio. Aumentando-se o comprimento do cátion, observa-se a expansão da cela unitária em comparação às zeólitas com cátion sódio pois cátions mais volumosos provocam variações no comprimento e nos ângulos das ligações O-Si-O e O-Al-O. Por análise termogravimétrica em atmosfera oxidante, observou-se que as zeólitas nanométricas exibem perfis de decomposição muito mais suaves, evidenciando as menores limitações difusionais. O mesmo foi observado em atmosfera inerte, indicando que a presença do O2 não influencia os eventos térmicos. Os materiais zeolíticos foram avaliados cataliticamente através da reação de condensação de Knoevenagel entre butiraldeído e cianoacetato de etila (3% m/m de catalisador) por 1 h. As zeólitas nanométricas apresentaram maiores conversões e maiores velocidades de reação no tempo zero que as microcristalinas, confirmando-se as vantagens de materiais com dimensões nanométricas.

Différents phosphates ont été préparés et testés pour la déshydratation de l'acide lactique en phase gaz. La sélectivité en acide acrylique dépend fortement de la température de réaction mais peu du temps de contact. A 380°C, des valeurs de sélectivité allant de 19 à 50% ont été mesurées pour des phosphates alcalino-terreux qui sont stables sur au moins 24 h. Des mesures d'acido-basicité ont montré que ces phosphates contiennent une forte proportion de sites de même force faible. De plus, une corrélation entre la sélectivité en acide acrylique et le ratio molaire acide/base a été établie : elle atteint 50% pour un rapport proche de 1 et diminue lorsque ce ratio augmente. L'acide lactique étant thermiquement peu stable (fonction acide très réactive), nous nous sommes tournés vers la conversion du lactate d'éthyle pur. Les sélectivités en produits de déshydratation sont largement favorisées avec une sélectivité maximale de 87% à 15% de conversion. Cependant, les catalyseurs sont moins actifs et se désactivent fortement sur 24 h. La désactivation peut être inhibée par ajout d'eau dans la phase gaz. La caractérisation de surface a montré que les vitesses de réaction augmentent avec le rapport P/M et a révélé la présence d'une phase amorphe hydroxylée correspondant à des mono, dihydrogénophosphates ou des polyphosphates. Les groupements P-OH présents dans cette phase sont consommés ou modifiés en condition de réaction pour les deux réactifs suggérant qu'ils constituent des sites actifs. Enfin, le suivi DRIFT des TPD-NH3 a permis de proposer que des paires acide-base (M2+ et P-O-) sont dosées dans ce cas. Elles constitueraient le site d'adsorption de l'acide lactique conduisant ensuite à un mécanisme de déshydratation de type E2 / Various alkaline-earth phosphates were prepared and evaluated for gas phase dehydration of lactic acid. Selectivity to acrylic acid strongly depends on the reaction temperature but not on the contact time. At 380 °C, values ranging from 19 to 49% were measured for alkaline–earth phosphates catalysts that are stable for at least 24 h. Acid–base properties measurements revealed that such phosphates contain high proportion of acidic and basic sites with same weak strength. Furthermore, correlation between selectivity to acrylic acid and the acid–base balance was clearly established: it was 50% for balance close to 1 and decreased increasing this parameter. Because of poor thermal stability of lactic acid, we then focused on the ethyl lactate conversion. Selectivities in dehydration products were much higher with a maxima of 87% at 15% conversion. However, the catalysts were less active and stable. The deactivation can be inhibited adding water in the gas phase. Surface characterization of catalysts showed that catalytic activities are correlated with the P/M ratio and revealed the presence of an hydroxylated amorphous phase corresponding to mono / dihydrogenophosphates or polyphosphates. The P-OH species present in these phases are consumed or modified for both reactants suggesting that they are active sites. Finally, NH3-TPD measurements followed by DRIFT suggested that acid base pairs (M2+ and P-O-) are then probed. Such pairs would constitute the adsorption site of lactic acid which then dehydrate in acrylic acid by an E2 mechanism