Examinando por Autor "Iglesias, José"

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Direct synthesis of titanium substituted mesostructured materials using non-ionic surfactants and titanocene dichloride
(2005) Melero, Juan A.; Arsuaga, Jesús M.; Frutos, Pilar de; Iglesias, José; Sainz, Javier; Blázquez, Sandra
Titanium-substituted mesoporous molecular sieves have been successfully synthesized using non-ionic surfactants and titanocene dichloride under strong acidic conditions. Structure-textural parameters of the synthesized materials were characterized by using X-ray diffraction and nitrogen adsorption techniques. The increasing of the gel solution pH allows an enhancement of titanium within the mesostructure without damage of textural properties and presence of extra-framework species. The high accessibility and dispersion of titanium centres has been proved by means of NH3 adsorption and DR UV-Vis spectroscopy, being compared with TS-1 material. The synthesized materials show high activity and selectivity in the selective epoxidation of 1-octene with ethylbenzylhydroperoxide as oxidant. Moreover, silylated samples promoted an increase of epoxide selectivity.
Low-grade oils and fats: effect of several impurities on biodiesel production over sulfonic acid heterogeneous catalysts
(ELSEVIER, 2011) Morales, Gabriel; Bautista, L. Fernando; Melero, J.A.; Iglesias, José; Sánchez-Vázquez, Rebeca
Different lipidic wastes and low-grade oils and fats have been characterized and evaluated as feedstocks for the acid-catalyzed production of FAME. The characterization of these materials has revealed significant contents of free fatty acids, Na, K, Ca, Mg, P, unsaponifiable matter and humidity. Arenesulfonic acid-functionalized SBA-15 silica catalyst has provided yields to FAME close to 80% in the simultaneous esterification-transesterification of the different feedstocks, regardless of their nature and properties, using methanol under the following reaction conditions: 160ºC, 2 h, 30 methanol to oil molar ratio, 8 wt% catalyst loading, and 2000 rpm stirring rate. Nevertheless, reutilization of the catalyst is compromised by high levels of impurities, especially because of deactivation by strong interaction of unsaponifiable matter with the catalytic sites. The conditioning of these materials by aqueous washing in the presence of cationic-exchange resin Amberlyst-15, followed by a drying step, resulted in a lower deactivation of the catalyst.
Production of Methyl Lactate with Sn-USY and Sn-β: Insights into Real Hemicellulose Valorization
(American Chemical Society, 2024-02-19) Jiménez-Martin, José M.; El Tawil-Lucas, Miriam; Montaña, Maia; Linares, María; Osatiashtiani, Amin; Vila, Francisco; Martín Alonso, David; Moreno, Jovita; García, Alicia; Iglesias, José
Potassium exchanged Sn-β and Sn-USY zeolites have been tested for the transformation of various aldoses (hexoses and pentoses), exhibiting outstanding catalytic activity and selectivity toward methyl lactate. Insights into the transformation pathways using reaction intermediates─dihydroxyacetone and glycolaldehyde─as substrates revealed a very high catalytic proficiency of both zeolites in aldol and retro-aldol reactions, showcasing their ability to convert small sugars into large sugars, and vice versa. This feature makes the studied Sn-zeolites outstanding catalysts for the transformation of a wide variety of sugars into a limited range of commercially valuable alkyl lactates and derivatives. [K]Sn-β proved to be superior to [K]Sn-USY in terms of shape selectivity, exerting tight control on the distribution of produced α-hydroxy methyl esters. This shape selectivity was evident in the transformation of several complex sugar mixtures emulating different hemicelluloses─sugar cane bagasse, Scots pine, and white birch─that, despite showing very different sugar compositions, were almost exclusively converted into methyl lactate and methyl vinyl glycolate in very similar proportions. Moreover, the conversion of a real hemicellulose hydrolysate obtained from Scots pine through a simple GVL-based organosolv process confirmed the high activity and selectivity of [K]Sn-β in the studied transformation, opening new pathways for the chemical valorization of this plentiful, but underutilized, sugar feedstock.
Synthesis of Sn-silicalite from hydrothermal synthesis of SiO2-SnO2 xerogels
(Microporous Mesoporous Mater. 119 (2009) 176-185, 2009) van Grieken, Rafael; Martos, Carmen; Sánchez-Sánchez, Manuel; Serrano, David P.; Melero, Juan A.; Iglesias, José; Cubero, Alvar G.
For the first time, the synthesis of Sn-zeolites starting from SiO2-SnO2 xerogels is described. The influence of several synthesis parameters in the physical-chemical properties of the xerogels and the zeolites subsequently generated has been investigated. Two different tin sources were assayed in the synthesis of xerogels (anhydrous SnCl4 and SnCl4¿5H2O) as well as two gelation agents (NH3 and TPAOH). Though both bases led SiO2-SnO2 xerogels mainly showing tetrahedrally coordinated tin centres, regardless the tin source, only TPAOH derived materials were easily transformed into MFI-type zeolites showing tin incorporation. On the other hand, NH3 gelified xerogels were difficult to crystallize, being this fact attributed to the retention of NH3 species in the xerogels because of the tin Lewis acidity, avoiding its inclusion in the zeolite crystalline framework. Studies on the crystallization time and temperature allowed to optimize the transformation of TPAOH gelified SiO2-SnO2 xerogels into tin-containing MFI zeolites showing isomorphically incorporated tin centres. The so-obtained materials were compared with conventionally synthesized SnS-1 zeolite showing better quality in terms of tin incorporation.