Examinando por Autor "Moreno, J."

Mostrando 1 - 5 de 5

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.
Direct synthesis of mesoporous M-SBA-15 (M = Al, Fe, B, Cr) and application to 1-hexene oligomerization
(ELSEVIER, 2009) van Grieken, R.; Escola, J. M.; Moreno, J.; Rodríguez, R.
M-SBA-15 materials (M = Al, B, Cr, Fe) were prepared by different direct synthesis methods, characterized and tested catalytically in the 1-hexene oligomerization reaction at 125ºC. Al-SBA-15 were synthesized within the range Si/Al=12-86 using aluminium isopropoxide as aluminium source. 27Al MAS NMR spectra point out that the three Al-SBA-15 samples contain more tetrahedral aluminium than octahedral and the ratio tetrahedral / octahedral diminished with increasing aluminium contents. B-SBA-15 was prepared with a Si/B=51-106 using two direct synthesis methods (sol-gel and hydrothermal) and three different boron sources (solid boric acid, aqueous boric acid and boron isopropoxide). The best results in terms of boron incorporation (Si/B = 51) were achieved with solid boric acid and the sol-gel method, although a lower degree of mesoscopic ordering was obtained compared to the hydrothermal procedure. 11B MAS NMR showed that trigonal boron is the principal coordination state obtained after calcination. Cr-SBA-15 was also achieved by direct synthesis method at different pH (1.5, 3, 5) but the incorporation degree was low, at best Si/Cr = 240 at pH = 5. UV-vis spectroscopy indicated that all Cr species were Cr6+ formed during the calcination step. Oligomerization of 1-hexene at 125ºC showed that the highest conversion (~ 30%) was attained over Al-SBA-15 (Si/Al=30) although Cr-SBA-15 material exhibited close conversion (21%) despite its low heteroatom content (Si/Cr = 240). Dimers were the major products over Al-SBA-15, Cr-SBA-15 and Fe-SBA-15 catalysts (selectivity ¿ 40%) while strikingly, sol gel B-SBA-15 lead mostly to heavy oligomers (> 60%), with less than 10 % of dimers.
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
Nitrogen and Sulphur Poisoning in Alkene Oligomerization over Mesostructured Aluminosilicates (Al-MTS, Al-MCM-41) and Nanocrystalline n-HZM-5
(ELSEVIER, 2008) Van Grieken, R.; Escola, J. M.; Moreno, J.; Rodriguez, R.
Oligomerization of 1-hexene in the presence of model poisons such as thiophene (700 - 7000 ppm of sulphur) and n-butylamine (25 - 250 ppm of nitrogen), either alone or in combination, were tested at 200ºC, 50 bar and using n-octane as solvent, over three catalysts: two uniformly mesostructured silica-alumina (Al-MTS, Al-MCM-41) and a nanocrystalline HZSM-5 zeolite. A content of 700 ppm of sulphur (adding thiophene) or/and 25 ppm of nitrogen (adding n-butylamine) after a TOS = 240 min. led towards roughly 10 -20% decrease in conversion over nanocrystalline HZSM-5, without significant changes in selectivity. On the contrary, a feeding of 1-hexene with 7000 ppm of sulphur and 250 ppm of nitrogen showed a drastic drop of conversion (from 90 to 27%) over n-ZSM-5 zeolite with a significant increase in the selectivity towards lighter oligomers (dimers, C7 - C8 isomers). This fact suggests that the strong acid sites of the zeolite are deactivated by poison adsorption and heavy oligomers/coke deposition both inside the micropores and over the external surface. In contrast, neither Al-MTS nor Al-MCM-41 catalysts were meaningfully affected by the poisons (especially Al-MTS), even for high concentration conditions, due to its high surface area and medium acid strength distribution. TG analyses of the mesoporous catalysts indicate weight losses of ~ 20-25%, with a contribution of 6 to 8% at 400 - 500ºC, assigned to the removal of deposited coke. Oligomerization of a FCC effluent under the same conditions over Al-MTS catalyst leads to a remarkable 58% conversion with a oligomer selectivity over 90% (32% of them C13 - C18).
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.