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Deposition and assembly of magnesium hydroxide nanostructures on zeolite 4A surfacesKoh, Pei Yoong 15 November 2010 (has links)
A deposition - precipitation method was developed to produce magnesium hydroxide / zeolite 4A (Mg(OH)₂ - Z4A) nanocomposites at mild conditions and the effect of processing variables such as precursor concentration, type of base added, and synthesis time on the composition, size, and morphology of the nanocomposite were studied. It was determined that the precursor concentration, basicity, and synthesis time had a significant effect on the composition, size, and morphology of the deposited magnesium hydroxide (Mg(OH)₂) nanostructures. The properties of the Mg(OH)₂ - Z4A such as surface area, pore volume and composition were characterized. Mg(OH)₂ - Z4A samples and bare zeolite 4A were dispersed in Ultem® polymer to form a mixed matrix membrane. The thermal and mechanical properties of the resulting films were investigated. It was found that the addition of rigid bare zeolites into the polymer decreased the mechanical properties of the polymer composite. However, some of these adverse effects were mitigated in the polymer composite loaded with Mg(OH)₂ - Z4A samples. Isotherms for the adsorption of Mg(OH)₂ petals on zeolite 4A were measured in order to determine the optimum conditions for the formation of magnesium hydroxide / zeolite 4A nanocomposites at ambient conditions. The loading of the Mg(OH)₂ can be determined from the adsorption isotherms and it was also found that the adsorption of Mg(OH)₂ on zeolite A occurs via 3 mechanisms: ion exchange, surface adsorption of Mg²⁺ ions, and surface precipitation of Mg(OH)₂. Without the addition of ammonium hydroxide, the predominant processes are ion exchange and surface adsorption of Mg²⁺ ions. In the presence of ammonium hydroxide, Mg(OH)₂ crystals are precipitated on the surface of zeolite 4A at moderate Mg²⁺ ions concentration and the loading of Mg(OH)₂ was found to increase with increasing Mg²⁺ ions concentration. A detailed examination of the interactions between Mg(OH)₂ and functional groups on the zeolite surface was conducted. Solid-state 29Si, 27Al, and 1H NMR spectra were coupled with FTIR measurements, pH and adsorption studies, and thermogravimetric analyses to determine the interactions of Mg(OH)₂ with surface functional groups and to characterize structural changes in the resulting zeolite after Mg(OH)₂ deposition. It was discovered that acid - base interactions between the weakly basic Mg(OH)₂ and the acidic bridging hydroxyl protons on zeolite surface represent the dominant mechanism for the growth of Mg(OH)₂ nanostructures on the zeolite surface.
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Synthèse et caractérisation de catalyseurs monométalliques et bimétalliques à base de métaux de transition pour les réactions d'hydrogénation chimiosélective / Synthesis and characterization of monometallic and bimetallic catalysts based on transition metals for chemoselective hydrogenation reactionsCiotonea, Carmen 01 July 2015 (has links)
La préparation de matériaux catalytiques, à base de métaux de transition (Ni, Co, Cu) supportés sur des supports à porosité organisée, performants pour la réaction d’hydrogénation chimiosélective du cinnamaldéhyde, a été étudiée. L’étude peut être divisée en deux parties distinctes, selon la nature du support, silicique ou aluminique. La première partie traite de la dispersion de métaux de transition sur des supports de type SBA-15.Dans le premier chapitre est présentée la préparation des catalyseurs par la méthode IWI-MD (Incipient Wetness Impregnation – Mild Drying). Plusieurs études, afin de valider l’efficacité de cette méthode, ont été menées : (i) influence de la texture du support, (ii) influence de la température et du temps de séchage; (iii) influence de la teneur en métal. Le deuxième chapitre rapporte l’étude de la préparation par la voie de déposition par précipitation. L’étude de la méthode d’infiltration des sels fondus, dite de Melt Infiltration (MI), optimisée afin d’assurer une infiltration complète du précurseur dans la porosité du support préalablement à la formation de la phase oxyde, est présentée dans le Chapitre 3. Finalement, le dernier chapitre du document traite de la dispersion sur des supports aluminiques mésoporeux ordonnés (AMO). Les matériaux catalytiques ont été préparés sur des supports AMO, obtenus par la voie d’auto-assemblage induit par évaporation (AAIE). Les paramètres étudiés sont : (i) l’effet de la texture du support, à partir d’alumines de différentes tailles de pores et (ii) l’effet du mode de déposition des métaux (par IWI-MD, MI ou TS). / The development of efficient transition metal based catalysts for the chemoselective hydrogenation reaction of cinnamaldehyde is studied. The active phases, studied in this work, are among the transition metals (Ni, Co and Cu), supported on porous ordered materials. This study can be divided in two different sections, according to the support nature. The first part concerns the dispersion of transition metals on SBA-15 type silica support. In the first chapter is presented the transition metal dispersion (Ni, Co and Cu) using IWI-MD (Incipient Wetness Impregnation –Mild Drying) method. Studies performed, to optimize active phase dispersion, are: (i) influence of support texture, (ii) influence of drying temperature, (iii) influence of drying time, (iv) influence of metal loading. In the second chapter, Ni, Co and Cu catalytic materials are prepared using deposition precipitation method. In the third chapter is described the transition metal dispersion using melt infiltration method (MI), optimized to ensure a complete infiltration of metallic precursors in the support porosity before oxide phase formation. The second section of the Ph.D. is related to the dispersion of transition metal over ordered mesoporous alumina (AMO) supports. Catalytic materials, based on Ni and Cu over AMO (obtained by EISA process - Evaporation Induced by Self-Assembly), are produced. Parameters studied are: effect of support texture, effect of preparation route (IWI-MD, MI and TS).
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