Examinando por Autor "Garcia, R.A."

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Catalytic activity of the beta zeolite with enhanced textural properties in the Friedel-Crafts acylation of aromatic compounds
(ELSEVIER, 2008) Garcia, R.A.; Serrano, D.P.; Vicente, G.; Otero, D.; Linares, M.
Friedel-Crafts acylation is widely used for the production of aromatic ketones applied as intermediates in both fine chemicals and pharmaceutical industries. The reaction is carried out by using conventional homogenous catalysts, which represents significant technical and environmental problems. The present work reports the results obtained in the Friedel-Crafts acylation of aromatic substrates (anisole and 2-methoxynaphthalene) catalyzed by Beta zeolite obtained by crystallization of silanized seeds. This material exhibits hierarchical porosity and enhanced textural properties. For the anisole acylation, the catalytic activity over the conventional Beta zeolite is slightly higher than with the modified Beta material, probably due to the relatively small size of this substrate and the weaker acidity of the last sample. However, the opposite occurred in the acylation of a bulky substrate (2-methoxynaphthalene), with the modified Beta showing a higher conversion. This result is interpreted due to the presence of a hierarchical porosity in this material, which favors the accessibility to the active sites.
Catalytic cracking of HDPE over hybrid zeolitic-mesoporous materials
(ELSEVIER, 2005) Garcia, R.A.; Serrano, D.P.; Otero, D.
The potential application of hybrid ZSM-5/MCM-41 materials for the catalytic degradation of high density polyethylene (HDPE) has been investigated and compared with the behavior of a standard Al-MCM-41 sample. Hybrid zeolitic-mesoporous materials were prepared from zeolite seeds obtained in different stages of ZSM-5 crystallization by variation of the synthesis time. The seeds were assembled around cetyltrimethyl ammonium bromide (CTAB) micelles to obtain hybrid materials having a combination of both zeolitic and mesostructured features. The samples so obtained have exhibited remarkable catalytic activity in the HDPE cracking despite the low temperatures (380 ºC) and catalyst loadings used (plastic/catalyst mass ratio =100), leading to polyolefin conversions higher than Al-MCM-41. The product distribution observed with the hybrid materials is closer to that typically obtained in the HDPE cracking over HZSM-5 zeolite, with a high proportion of light hydrocarbons. Moreover, the products present a high content of C2-C5 olefins, which is an interesting result regarding its possible use as raw chemicals. Increasing the zeolitic crystallinity of the hybrid materials causes an enhancement in the production of heavier products with boiling points within the gasoline range.
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.