Examinando por Autor "Iglesias, J."

Mostrando 1 - 7 de 7

Direct synthesis and post-oxidation of SBA-15 and MCM-41 functionalized with butenyl groups.
(ELSEVIER, 2005) Garcia, R.A.; van Grieken, R.; Iglesias, J.; Morales, V.; Martin, J.
Olefins and derivatives are interesting compounds to anchor onto the surface of silica supports since their reactivity allow to form a large variety of organic functionalities. In this work, the synthesis of mesostructured silicas (MCM 41 and SBA 15 type materials) functionalized with butenyl groups is studied through the use of post synthetic grafting or direct synthesis procedures. Results confirm the higher functionalization degree achieved in the final mesostructured materials when using direct synthesis procedures. Unlike MCM 41 materials, which become microporous when high organic content are attached on, SBA 15 type butenyl functionalized silicas keep the features of a mesoporous solid. Post synthetic and in-situ oxidations of butenyl groups during the preparation of the mesostructured silicas have been carried out using H2O2 as oxidant, leading to materials functionalized with glycol species attached to inorganic mesoporous materials, which are attractive to be used as supports for anchoring different catalytic species.
Efficient conversion of levulinic acid into alkyl levulinates catalyzed by sulfonic mesostructured silicas
(ELSEVIER, 2013) Melero, J.A.; Morales, G.; Iglesias, J.; Paniagua, M.; Hernández, B.; Penedo, S.
Sulfonic mesoporous silicas have demonstrated an outstanding catalytic performance in the esterification of levulinic acid with different alcohols to produce alkyl levulinates, a family of chemicals considered to be excellent oxygenated fuel extenders for gasoline, diesel and biodiesel. Catalyst screening indicated that propylsulfonic acid-modified SBA-15 material was the most active one, among tested materials, due to a combination of moderately strong sulfonic acid sites with relative high surface hydrophobicity. Under optimized reaction conditions (T = 117 ºC, ethanol/levulinic acid molar ratio = 4.86/1 and catalyst/levulinic acid = 7 wt.% ) almost 100% of levulinic acid conversion was achieved after 2 h of reaction, being negligible the presence of levulinic acid by-products or ethers coming from intermolecular dehydration of alcohols. The catalyst has been reused, without any regeneration treatment, up to three times keeping almost the high initial activity. Interestingly, a close catalytic performance to that achieved using ethanol has been obtained with bulkier alcohols.
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.
Synthesis and characterization of SBA-15 materials functionalized with olefinic groups and subsequent modification through oxidation procedures
(ELSEVIER, 2010) van Grieken, R.; Iglesias, J.; Morales, V.; García, R.A.
The synthesis of alkenyl-SBA-15 materials has been carried out through different methodologies. The direct-synthesis method used for the functionalization of SBA-15 involving the co-condensation of the alkenyl-silicon precursor together with silicon alkoxides is clearly superior than any other post-synthetic pathway, even if acid catalysts are used to drive the post-synthetic grafting of olefin groups. The direct-synthesis methodology has been deeply studied within this work, involving the influence of the silica precursor prehydrolysis time, and the loading of different olefin-silanes on the quality of the mesostructure. Small olefinic functionalities, like vinyl groups, can be incorporated in a very efficient manner up to achieve organic loadings as high as 50% mole of the olefin precursor to TEOS. The modification of these alkenyl groups through oxidation can be accomplished through post-synthetic oxidation of the olefinic group or even through an in-situ methodology where the oxidant ¿ hydrogen peroxide ¿ is added together with the rest of the precursor into the synthesis gel to lead complete oxidation of the double bonds towards glycolic functionalities. The resultant materials show potential as hydrophilic adsorbents and catalytic supports.
Synthesis of titanium containing periodic mesoporous organosilica
(ELSEVIER, 2007) Melero, J.A.; Iglesias, J.; Sáinz-Pardo, J.; Arsuaga, J.M.
Organic-inorganic mesostructured materials were functionalized with titanium by direct synthesis under strong acidic conditions using non-ionic surfactants as structure directing agent and titanocene dichloride as titanium precursor. Materials with different organic content were synthesized with a high mesoscopic order and with incorporation of titanium species in isolated framework positions. The physicochemical properties of the synthesized samples were assessed by different characterization techniques including XRD, 29Si MAS-NMR, nitrogen adsorption/desorption experiments and DR UV-VIS spectroscopy.
Synthesis, characterization and catalytic activity of highly dispersed Mo-SBA-15
(ELSEVIER, 2007) Melero, J.A.; Iglesias, J.; Arsuaga, J.M.; Sainz-Pardo, J.; Frutos, Pilar de; Blázquez, Sandra
Molybdenum-containing SBA-15 materials have been prepared using a co-condensation method with a wide range of metal loadings under acidic conditions and using non-ionic surfactants. These materials display good catalytic activity in the epoxidation of olefins with alkyl hydroperoxides, being the catalytic activity correlated with the nature of supported molybdenum species. The immobilized metal species show different stabilities against leaching depending on their nature. Reutilization catalytic tests indicate that some fraction of the molybdenum show a high stability and it seems to be responsible for the major part of the catalytic activity of these materials. Stable molybdenum species use in a very efficient manner the alkyl hydroperoxide in the epoxidation of olefins whereas leached species leads to non-oxidative consumption of the oxidant and promote secondary reactions.
Zr-SBA-15 Acid Catalyst: Optimization of the Synthesis and Reaction Conditions for Biodiesel Production from Low-grade Oils and Fats
(Elsevier, 2012-11) Melero, J.A.; Bautista, L.F.; Iglesias, J.; Morales, G.; Sánchez-Vázquez, R.
The production of biodiesel by methanolysis of highly acidic crude palm oil has been optimized for the Zr-SBA-15 heterogeneous acid catalyst. A dual optimization procedure has been carried out using surface response methodology and selecting the yield towards fatty acid methyl esters (FAMEs) as main response factor. Selected target variables for the optimization were: acidity of the synthesis media, zirconium loading, ageing temperature (all three for the synthesis of the catalyst); and temperature, methanol to oil molar ratio, catalyst loading (for the reaction tests). Quadratic equations were obtained for both models and their statistical analysis led to the optimal conditions for Zr-SBA-15 synthesis (0.67 N HCl media concentration, 130ºC ageing temperature, 10 Si/Zr molar ratio), and for the transesterification reaction conditions (209ºC, 12.45 wt% catalyst loading, 45.8 methanol to oil molar ratio). Under these optimized conditions FAME yield reached 92 mol% after 6 h. Additionally, reusability tests revealed that the optimized Zr-SBA-15 catalyst displays an excellent reaction stability, being fully regenerated after calcination at 450ºC. Moreover, the high catalytic activity and stability achieved with crude palm oil is retained when using waste cooking oil (WCO) or low-grade fats such as category-1 fat, waste lard and mixed fats, leading to FAME yields over 90% after 6 hours, for each raw material, and with acidities in the final product lower than 2.5 mg KOH per gram.