Examinando por Autor "Carrero, A."

Mostrando 1 - 6 de 6

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.
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
Ethylene polymerization over supported MAO/(nBuCp)2ZrCl2 catalysts:Influence of support properties.
(ELSEVIER, 2007) Van Grieken, R.; Carrero, A.; Suarez, I.; Paredes, B.
The catalytic system methylaluminoxane (MAO) and bis(n-butylcyclopentadienyl)zirconium dichloride ((nBuCp)2ZrCl2) was immobilized on commercial silica, silica-alumina and aluminophosphate calcined at different temperatures. The properties of the supports were determined by using N2 adsorption-desorption isotherms at 77 K, FT-IR spectroscopy and SEM. After aluminium and zirconium impregnation, the catalysts were analyzed by ICP-AES, FT-IR and UV-Vis spectroscopy. Ethylene polymerizations were carried out in a Schlenk tube at 70 ºC and 1.2 bar of ethylene pressure. The polyethylene obtained was characterized by GPC, DSC and SEM. Catalysts supported on silica-alumina exhibited higher polymerization activity than those supported on silica and aluminophosphate. Besides, the activity of MAO/(nBuCp)2ZrCl2 catalytic system supported on silica-alumina and aluminophosphate decreased strongly with support calcination temperature, while remained almost constant when silica was employed as support. All these experimental features suggest a role of the support acid properties and hydroxyl group population in the generation of active polymerization species.
Hybrid zeolitic-mesostructured materials as supports of metallocene polymerization catalysts
(ELSEVIER, 2012) Carrero, A.; Grieken, Rafael van; Paredes, B.
The potential application of hybrid ZSM-5/Al-MCM-41 zeolitic-mesostructured materials as supports of metallocene polymerization catalysts has been investigated and compared with the behaviour of standard mesoporous Al-MCM-41 and microporous ZSM-5 samples. Hybrid zeolitic-mesostructured solids were prepared from zeolite seeds obtained with different Si/Al molar ratios (15, 30 and 60), which were assembled around cetyltrimethylammonium bromide (CTAB) micelles to obtain hybrid materials having a combination of both zeolitic and mesostructured features. (nBuCp)2ZrCl2/MAO catalytic system was impregnated onto the above mentioned solid supports and tested in ethylene polymerization at 70 Cº and 5 bar of ethylene pressure. Supports and heterogeneous catalysts were characterized by X-ray powder diffraction, nitrogen adsorption-desorption isotherms at 77 K, transmission electron microscopy, 27Al-MAS-NMR, ICP-atomic emission spectroscopy and UV-vis spectroscopy. Catalysts supported over hybrid ZSM-5/Al-MCM-41 (Si/Al = 30-60) exhibited the best catalytic activity followed by those supported on Al-MCM-41 (Si/Al = 30-60). However, catalyst supported on ZSM-5 gave lower polymerization activity because of its microporous structure with narrower pores and lower textural properties than hybrid and mesoporous materials. Although higher acid site population shown by hybrid materials could contribute to the stabilization of the metallocene system on the support, in this case their better catalytic performance is mainly ascribed to the larger textural properties.
Life cycle assessment of H2-selective Pd membranes fabricated by electroless pore-plating
(Elsevier, 2021) Martinez-Diaz, D.; Leo, P.; Sanz, R.; Carrero, A.; Calles, J.A.; Alique, D.
Pd-based membranes are attracting great attention to reach ultra-pure hydrogen in independent separators or combined with catalysts in membrane reactors. Many advances have been proposed for their fabrication over the last few years, reaching relatively thin Pd-films onto porous substrates with high permeation capacities and mechanical stability, although their commercialization and penetration in the industry are still scarce. At this point, it is important to complete all these technological advances with data about related economic and environmental implications during their fabrication to detect possible bottlenecks and select the best strategy. In this context, the current study presents for the first time a life cycle assessment focused on the preparation of Pd-based composite-membranes by Electroless Pore-Plating (ELP-PP). Two different types of composite membranes supported onto porous stainless steel tubes are analyzed, including or not an additional CeO2 intermediate layer between the support and the Pd-film. Precise experimental data of the fabrication process at laboratory-scale were considered to account for both materials and energy requirements. Thereafter, the environmental impacts were estimated through ReCiPe methodology by using the software Simapro 8.5. The results evidence that climate change (CC), human toxicity (HT), acidification (AC), freshwater ecotoxicity (FWE), metal depletion (MD) and fossil fuel resources depletion (FD) are the most relevant environmental impacts generated during the manufacturing of the Pd-based membrane. Under this perspective, palladium deposition appears as the manufacturing step with the highest impacts. It can be explained by the metal consumption and the high-energy consumption required for deposition cycles. Thus, the electricity mix of the country where the factory is located is critical to minimize the environmental impacts. For this reason, European countries are expected to be the most favorable ones for membrane fabrication. Finally, comparing both membrane types (with or without a CeO2 intermediate layer), it can be stated that the incorporation of the ceramic layer noticeably reduces the necessary amount of Pd to reach a fully dense membrane and therefore the associated environmental impacts.
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.