Minieri, Luciana (2016) Sol-gel synthesis of inorganic and hybrid transition metal oxides based materials. [Tesi di dottorato]

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Item Type: Tesi di dottorato
Resource language: English
Title: Sol-gel synthesis of inorganic and hybrid transition metal oxides based materials
Date: 27 March 2016
Number of Pages: 97
Institution: Università degli Studi di Napoli Federico II
Department: Fisica
Scuola di dottorato: Ingegneria industriale
Dottorato: Tecnologie innovative per materiali, sensori ed imaging
Ciclo di dottorato: 28
Coordinatore del Corso di dottorato:
Aronne, AntonioUNSPECIFIED
Date: 27 March 2016
Number of Pages: 97
Keywords: Sol-gel synthesis; ZrO2-based hybrid material; Ruthenium-based mixed oxides; TG-DTA; FTIR spectroscopy; UV-vis DR spectroscopy; X-ray diffraction
Settori scientifico-disciplinari del MIUR: Area 03 - Scienze chimiche > CHIM/07 - Fondamenti chimici delle tecnologie
Date Deposited: 08 Apr 2016 13:41
Last Modified: 09 Jan 2017 02:00

Collection description

The research activity of this PhD project was focused on the preparation by sol-gel synthesis of hybrid (ZrO2-acetylacetonate, HSGZ) and inorganic (Nb2O5∙SiO2 and Ru/RuO2@Nb2O5∙SiO2) mixed-oxide materials. HSGZ was prepared at room temperature by a sol-gel synthesis using suitable process conditions to produce a homogeneous chemical gel. The thermal stability of the material was investigated by thermogravimetry-differential thermal analysis, and Fourier transform infrared spectroscopy. In addition, HSGZ was tested in the oxidative degradation of four different phenoxy herbicides (2-methyl-4-chlorophenoxyacetic acid (MCPA), 4-(4-chloro-2-methylphenoxy)butanoic acid (MCPB), 4-chlorophenoxyacetic acid (4-CPA) and 2,4-dichlorophenoxyacetic acid (2,4 D)). For each herbicide, a virtually complete removal in about 3 days without light irradiation at room temperature was achieved. A long-term application of the HSGZ catalyst assessed by repeated-batch tests was achieved, as well. Finally, in order to clarify the mechanism of action of this catalyst, the physico-chemical properties were investigated by using suitable spectroscopic techniques, such as electron paramagnetic resonance. The promising results about the striking capability of this material to catalyze oxidative degradation reactions in absence of light and without any thermal pretreatment lead the path toward further development of HSGZ and related hybrid materials for ROS-based energy and environmental applications. Part of my research activity was devoted to investigate the influence of the preparation procedure on the structure and the properties of Nb2O5•SiO2 materials containing about the same Nb2O5 amount (19 % wt.) but obtained by different synthetic routes with special attention to their catalytic activity in the epoxidation of methyl oleate with hydrogen peroxide. The catalytic performance of the niobium oxide-based materials can be controlled by modulating the acidic properties, by regulating the structure and in turn, the preparation method. In detail, the catalytic activity of the catalyst prepared by impregnation do not differ substantially from that of commercial Nb2O5. The performances of Nb-supported catalysts prepared by sol-gel depend on the synthesis process parameters. The high dispersion of the active NbOx species obtained by this preparation method gives very higher selectivity than in the case of commercial Nb2O5. Morphological and structural characterization of the catalysts helped justifying the obtained catalytic results in terms of activity and selectivity. Ru-based mixed oxide (Ru/RuO2@Nb2O5-SiO2) was obtained by an innovative sol-gel synthesis wholly performed at room temperature and characterized by both easy handling of precursors and the lack of toxic or pollutant reactants. The surface area and the morphological characteristics of the material were controlled adding different amounts (0.04 and 0.16 wt. %) of a nonionic surfactant (polyethylene glycol hexadecyl ether, Brij-C10) directly in the starting solution of precursors. The influence of Brij-C10 incorporation on porous structure, size and dispersion of ruthenium nanoparticles were investigated in detail by structural, morphological and textural characterization. It was demonstrated that the differences in particle size of ruthenium oxide and their dispersion are likely due to the different grain growth rate during the synthesis caused by the addition of surfactant. These results indicate that Brij-C10 actually plays a role of complexing agent of the metallic species and not only as pore directing agent, as proven by textural analysis. The surfactant, indeed, contribute to increase the SSA and PSD and to obtain a high dispersion of metal species. These materials act as bifunctional catalysts thanks to their acidic and redox functionalities in the hydrogenation of levulinc acid to γ-valerolactone. All catalysts showed the same results in both LA conversion and GVL yield, indicating that the presence of surfactant did not influence the catalytic performance. Therefore, reusability tests clearly indicated that the catalyst without Brij-C10 is very stable under the adopted conditions and no activity loss was ascertained. On the contrary, the presence of surfactant induced a significant deactivation already at its second reuse due to the adsorption of organic species.


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