Examinando por Autor "Melero, J. A."

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Crystallization mechanism of Fe-MFI from wetness impregnated Fe2O3-SiO2
(ELSEVIER, 2004) Melero, J. A.; Calleja, G.; Martínez, F.; Molina, R.; Lázár, K.
The crystallization mechanism of Fe-MFI zeolite synthesized from amorphous Fe2O3- SiO2 xerogels wetness impregnated with aqueous TPAOH solutions has been studied. Samples with different degrees of crystallinity were prepared and characterized by means of conventional techniques. Activity and stability of these iron-containing samples has been tested in the catalytic wet peroxide oxidation (CWPO) of phenolic aqueous solutions. The crystallization mechanism involves a partial dissolution of the initial xerogel to yield an amorphous material. Nucleation and growth of the MFI phase is effected by reorganisation of the amorphous phase, although crystal growth also involves the incorporation of iron and silicon species during the last stage of the crystallization. A highly crystalline Fe-silicalite material is obtained after 3 hours of synthesis at 170 ºC. Spectroscopic studies reveal that iron species are in framework positions (isomorphously substituted) in this highly crystalline material. In addition, the environment of Fe atoms as well as textural properties of the samples is dramatically modified along the crystallization affecting significantly to their catalytic activity and stability in CWPO processes.
Iron species incorporated over different silica supports for the Phenol
(ELSEVIER, 2007) Martínez, F.; Calleja, G.; Melero, J. A.; Molina, R.
Iron-containing catalysts have been prepared following different synthesis routes and silica supports (amorphous, zeolitic and mesostructured materials). Activity and stability of these materials were assessed on the photo-Fenton degradation of phenolic aqueous solutions using near UV irradiation (higher than 313 nm) at room temperature and initial neutral pH. Their catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversions. Aromatic compounds and carboxylic acids as by-products coming from incomplete mineralization of phenol as well as the efficiency of each catalytic system in the use of the oxidant were also studied. Stability of the materials throughout the photo-Fenton reaction was evaluated in terms of metal leachibility. Activity and stability depend on the environment of iron species and features of silica support. The evolution of pH with the reaction time and their relationship with TOC degradation and leaching degree has been discussed. A nanocomposite material of crystalline iron oxides supported over mesostructured SBA- 15 material is shown the most successful catalyst for degradation of phenolic aqueous solutions by photo-Fenton processes, achieving an outstanding overall catalytic performance accompanied with a noteworthy stability.
Nanocomposite Fe203/SBA-15: An efficient and stable catalyst for the catalytic wet peroxidation of phenolic aqueous solutions
(ELSEVIER, 2007) Melero, J. A.; Calleja, G.; Martínez, F.; Molina, R.; Pariente, M. I.
In this work, the catalytic wet peroxide oxidation of phenolic aqueous solutions over a novel Fe2O3/SBA-15 nanocomposite material was deeply studied. The catalytic performance was monitored in terms of aromatics and total organic carbon (TOC) removals. In order to reduce the major operation cost, significant operating reactions parameters that affect remarkably the overall catalytic performance of these processes, such as temperature and hydrogen peroxide concentration, were studied by means of a design of experiments. High temperature is necessary to obtain a fast and complete degradation of aromatic compounds. At 100ºC, moderate catalyst loading and hydrogen peroxide concentration (0.6 g/L and 75 % of stoichiometric amount for phenol mineralization, respectively) were enough to achieve a total removal of aromatic compounds and remarkable TOC mineralization under non-controlled pH conditions. Resistance of iron species to be leached out into the aqueous solution has been also carefully examined with the purpose of elucidating the influence of different reaction parameters (temperature, oxidant concentration and pH). A schematic view of the heterogeneous catalytic peroxidation of phenol over this novel catalyst has been proposed. Finally, the stability of the catalyst has been established by recycling studies.