Examinando por Autor "Calleja, G."

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Activity and resistance of iron-containing amorphous, zeolitic and mesoestructured materials for wet peroxide oxidation of phenol
(ELSEVIER, 2005) Calleja, G.; Melero, J.A.; Martínez, F.; Molina, R.
Iron containing materials have been prepared following several strategies of synthesis and using different silica supports (amorphous, zeolitic and mesostructured materials). Activity and stability of these materials was evaluated on heterogeneous Fenton-type processes for the removal of phenol under mild reaction conditions (T=100º, P=0.1 MPa). Their catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversions, by-products distribution (aromatics compounds and carboxylic acids) and degree of metal leached into the aqueous solution. The nature and local environment of iron species is strongly dependent on the synthetic route, which dramatically influences on their catalytic performance. Crystalline iron oxide species supported over mesostructured SBA-15 materials have demonstrated to be the most interesting catalysts for phenol degradation according to its high organic mineralization, low sensitive to be leached out and better oxidant efficiency for Fenton like reactions.
Chromium supported onto swelled Al-MCM-41 materials: a promising catalysts family for ethylene polymerization
(ELSEVIER, 2005) Calleja, G.; Aguado, José; Carrero, A.; Moreno, J.
Swelled MCM-41 and Al-MCM-41 materials with large pore size and pore volume were synthesized and used as supports to prepare novel chromium catalysts for ethylene polymerization. Aluminium incorporation favoured chromium anchorage onto MCM-41 surface. Attachment of Cr species resulted from H-bonding of cuasi ¿-electron system of the acetylacetonate ligands with hydroxyls groups or with electron acceptor centres like Al3+. Chromium supported onto swelled Al-MCM-41 showed higher ethylene polymerization activity than conventional Cr/SiO2 catalysts tested in the same conditions. Properties of both obtained polymers were similar, indicating the formation of linear high density polyethylene.
CO2 adsorption performance of aminofunctionalized SBA-15 under post-combustion conditions
(Elsevier, 2013) Sanz-Pérez, E.S.; Olivares-Marín, M.; Arencibia, A.; Sanz, R.; Calleja, G.; Maroto Valer, M.M.
Carbon dioxide adsorbents prepared from SBA-15 mesostructured silica functionalized with amino groups have been tested under a simulated gas mixture similar to that of a coal-fired thermal power plant. SBA-15 material was functionalized by grafting with aminopropyl-trimethoxysilane (AP (N)) and diethylene-triamine-trimethoxysilane (DT (NNN)), and by impregnation with polyethyleneimine (PEI) and tetraethylenepentamine (TEPA). CO2 adsorption performance was measured in both a thermobalance and in a fixed bed. A thorough study of the adsorption behaviour was carried out, including the influence of conditions found in real post-combustion operation processes, such as diluted CO2 concentration, presence of SO2 and moisture in the flue gas. The reutilization of the adsorbent by successive adsorption-desorption experiments has also been tested. Grafted materials and samples impregnated with around 50 % organic amount or higher, showed a small influence of the dilution of CO2 in the feed gas on their CO2 uptake. Adsorption capacity after 10 cycles remains almost unaltered for grafted and PEIimpregnated solids and moderately decreases for TEPA-impregnated adsorbent. CO2 adsorption capacity decreased significantly with the presence of 1,000 ppm SO2 for up to 5 cycles, finding a direct correlation with the nitrogen content of the sorbents. Humid conditions (5 % moisture) do not significantly affect adsorption capacity of grafted samples, but improve the CO2 uptake of impregnated adsorbents about 50-60 %, obtaining an adsorption capacity of 16.2 wt. % CO2 (3.7 mmol CO2/g) for sample SBA-TEPA (50) in a humid diluted CO2 stream (15 % CO2) at 45 ºC and 1 bar.
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.
Ethylene polymerization over chromium supported onto SBA-15 mesoporous materials
(ELSEVIER, 2005) Calleja, G.; Aguado, José; Carrero, A.; Moreno, J.
Ethylene polymerization catalysts have been prepared by incorporation of chromium (III) acetylacetonate onto siliceous SBA-15 swelled mesoporous materials. Catalysts characterization includes DRX, FTIR, UV-vis spectroscopy, nitrogen physisorption, TGA and ICP analysis. Chromium anchorage through H-bonds was observed in Cr/SBA-15 catalyst prepared by incipient wetness impregnation. On the contrary, when catalysts were prepared by grafting, a ligand exchange reaction may occur. For similar chromium contents, catalyst prepared by grafting showed higher polymerization activity than catalyst prepared by incipient wetness impregnation. Regarding polymer properties, Cr/SBA-15 catalyst prepared by impregnation gave polyethylene with slightly higher molecular weight, polydispersity, bulk density and melting temperature than polyethylene obtained from grafted catalyst
Heterogeneous photo-Fenton degradation of phenolic aqueous solutions
(ELSEVIER, 2005) Martínez, F.; Calleja, G.; Melero, J.A.; Molina, R.
A novel iron-containing mesostructured material has been successfully tested for the heterogeneous photo-Fenton degradation of phenolic aqueous solutions using near UV-visible irradiation (higher than 313 nm) at room temperature and close to neutral pH. This catalyst is a composite material that contains crystalline hematite particles embedded into the mesostructured SBA-15 matrix in a wide distribution of size (30 ¿ 300 nm) and well dispersed ionic iron species within the siliceous framework. The outstanding physicochemical properties make this material a promising photocatalyst leading to better activity than other unsupported iron oxides. An experimental design model has been applied to assign the weight of catalyst and hydrogen peroxide concentrations in the photo-Fenton processes over this particular material. The catalytic performance has been monitored in terms of aromatics and total organic carbon (TOC) conversions, whereas the catalyst stability was evaluated according to the metal leached into the aqueous solution. Hydrogen peroxide concentration plays an important role in the stability of the iron species, preventing their leaching out into the solution, in contrast to the effect shown in typical dark Fenton reaction. The homogeneous leached iron species result in very little contribution to the overall photocatalysis process. Catalyst loadings of 0.5 g/L and concentration of hydrogen peroxide close to the stoichiometric amount have yielded a total abatement of phenol and a remarkable organic mineralization.
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.
Preparation of titanium molecular species supported on mesostructured silica by different grafting methods
(ELSEVIER, 2002) Calleja, G.; van Grieken, R.; García, R.; Melero, J.A.; Iglesias, J.
Titanium supported on SBA-15 mesoporous silica has been synthesised containing different titanium loadings prepared by chemical grafting using titanocene dichloride as precursor and over different treated silica surfaces. A comparative study using MCM-41 mesoporous silica as support is also reported. The type of silica support and its surface properties as well as the initial concentration of Ti precursor in the organic solution influences clearly the incorporation of Ti species. The materials after grafting treatment were characterized by different conventional techniques including XRD, FT-IR DR UV-Vis and nitrogen adsorption. The titanium containing SBA-15 silica shows hexagonal mesoscopic order and pore sizes up to 70 Å with surface areas up to 600 m2/g and titanium content ranging from 1 to 3 wt. %. DR UV-Vis of Ti containing SBA-15 silica after removal of the organic ligand shows the presence of Ti isolated species tetrahedrally coordinated and the absence of bulky TiO2 phases. Likewise, these materials upon calcination were catalytically active for the epoxidation of styrene with TBHP exhibiting a significant selectivity toward the epoxide.
Preparation, characterization and testing of Cr/AlSBA-15 ethylene polymerization catalysts
(ELSEVIER, 2007) Calleja, G.; Aguado, José; Carrero, A.; Moreno, J.
Ethylene polymerization catalysts have been prepared by grafting chromium (III) acetylacetonate onto SBA-15 (Si/Al = ¿, 156, 86 and 30) mesoporous materials. Aluminium incorporation favoured chromium anchorage onto SBA-15 surface as chromate and dichromate. The reduction temperature, determined by hydrogen TPR, decreased with the Si/Al ratio. Attachment of Cr species onto AlSBA-15 surface resulted from the interaction of hydroxyl groups with the acetylacetonate ligands through H-bonds, while a ligand exchange reaction may occur over siliceous SBA-15. The polymerization catalyst corresponding to AlSBA-15 (Si/Al = 30) support is almost four times more active than a conventional Cr/SiO2 Phillips catalyst. However, very poor polymerization activity was obtained with chromium supported on aluminium free SBA-15 material. Polymers obtained with all catalysts showed melting temperatures, bulk densities and high load melt indexes indicating the formation of linear high-density polyethylene.