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Lopez F.A.,CSIC - National Center for Metallurgical Research | Rodriguez O.,CSIC - National Center for Metallurgical Research | Alguacil F.J.,CSIC - National Center for Metallurgical Research | Garcia-Diaz I.,CSIC - National Center for Metallurgical Research | And 3 more authors.
Journal of Analytical and Applied Pyrolysis

This paper examines the recovery of carbon fibres from a composite used in the aeronautical industry, via a combined process of thermolysis and gasification in an air atmosphere. The waste was thermolysed at 500 C, 600 C or 700 C in a pilot plant to determine the optimum thermolysis temperature. The solid residues produced - char covered carbon fibres - were characterized by SEM and XPS. The optimum time for the gasification of the char covering the fibres was determined in a combined thermolysis/gasification assay. After thermolysis at the optimum temperature (500 C), 12 l/h of pure air were injected into the reactor and char gasification performed at 500 C for 30-180 min. The optimum gasification time was 30 min. Longer gasification times led to the production of fibres of smaller diameter with oxidized surfaces and reduced tensile strength. The optimally recovered fibres showed about 70% of the tensile strength of virgin fibres and some 90-96% of their elasticity. © 2013 Elsevier B.V. All rights reserved. Source

Rojas A.,CSIC - Institute of Materials Science | Gomez-Hortiguela L.,Institute Catalisis y Petroleoquimica ICP CSIC | Camblor M.A.,CSIC - Institute of Materials Science
Journal of the American Chemical Society

A series of doubly charged structure-directing agents based on two methylimidazolium moieties linked by a linear bridge of n = 3,4,5, or 6 methylene groups has been used in the synthesis of pure silica zeolites in the presence of fluoride. All of them yielded zeolite TON while only the one with n = 4 was able to produce also zeolite MFI at highly concentrated conditions. In this MFI zeolite, two distinct 19F MAS NMR resonances with about equal intensity were observed, indicating two different chemical environments for occluded fluoride. With the singly charged 1-ethyl-3-methylimidazolium cation, which can be formally considered as the "monomer" of the bis-imidazolium cation with n = 4, TON and MFI were also obtained, and again two 19F MAS NMR resonances now with largely dissimilar intensities were observed in MFI. Molecular mechanics simulations support a commensurate structure-direction effect for n = 4 in MFI, with each imidazolium ring, in two different orientations, sitting close to the [4 15 26 2] cage. Periodic DFT calculations suggest that F in MFI resides always in the [4 15 26 2] cages, with the different 19F resonances observed being due to the different orientation of the closest imidazolium ring. © 2012 American Chemical Society. Source

Torres C.C.,University of Concepcion | Alderete J.B.,University of Concepcion | Pecchi G.,University of Concepcion | Campos C.H.,University of Concepcion | And 4 more authors.
Applied Catalysis A: General

A series of Ti-modified MCM-41 supports and their respective Au catalysts were prepared and characterized to study the effect of titanium into the support and on the characteristics of the Au surface species for heterogeneous hydrogenation of aromatic nitrocompounds. The systems were characterized by X-ray diffraction, Infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), diffuse reflectance UV-vis (DRUV-vis), N2 adsorption-desorption isotherms, ICP-MS and X-ray photoelectron spectroscopy (XPS). Additionally, these catalysts were tested for the hydrogenation of nitrobenzene in a batch-type reactor using ethanol as the solvent at 25 °C. Based on a combined FT-IR and DRUV-vis was possible to conclude that the Ti(IV) is incorporated into the framework of MCM-41 and Ti-containing MCM-41 catalysts were more active than an MCM-41 unmodified catalyst. The Ti(X)-MCM-41 supports prepared with Ti 2.0 wt% incorporation showed the best catalytic performance, which was attributed to an optimal number of isolated Ti sites that increased the Au stability on the support surface. For this system, the effect of the H2 pressure, solvent nature and recyclability of the catalyst was also studied. Finally, a quantitative structure property relationship (QSPR) model was obtained for the catalytic activities of para-substituted nitrobenzenes. The multilinear model considered two parametric descriptors: the sigma constant (σ) and the hydrophobic π-constant, which account for the electronic and hydrophobic effect of the substituents. © 2016 Elsevier B.V.All rights reserved. Source

Lustemberg P.G.,CONICET | Pan Y.,CAS Institute of Physics | Shaw B.-J.,University College London | Grinter D.,University College London | And 5 more authors.
Physical Review Letters

Surface defects are believed to govern the adsorption behavior of reducible oxides. We challenge this perception on the basis of a combined scanning-tunneling-microscopy and density-functional-theory study, addressing the Au adsorption on reduced CeO2-x(111). Despite a clear thermodynamic preference for oxygen vacancies, individual Au atoms were found to bind mostly to regular surface sites. Even at an elevated temperature, aggregation at step edges and not decoration of defects turned out to be the main consequence of adatom diffusion. Our findings are explained with the polaronic nature of the Au-ceria system, which imprints a strong diabatic character onto the diffusive motion of adatoms. Diabatic barriers are generally higher than those in the adiabatic regime, especially if the hopping step couples to an electron transfer into the ad-gold. As the population of O vacancies always requires a charge exchange, defect decoration by Au atoms becomes kinetically hindered. Our study demonstrates that polaronic effects determine not only electron transport in reducible oxides but also the adsorption characteristics and therewith the surface chemistry. © 2016 American Physical Society. Source

Torres C.,University of Concepcion | Campos C.,University of Concepcion | Fierro J.L.G.,Institute Catalisis y Petroleoquimica ICP CSIC | Oportus M.,University of Concepcion | Reyes P.,University of Concepcion
Catalysis Letters

Recently, gold has been proposed as an active phase for the hydrogenation of nitro-arenes. This metal has been rarely used in hydrogenation reactions because gold does not possess hydrogen chemisorption capacity. However, small gold particles behave differently and they may be able to chemisorb hydrogen to same extent, leading to possible activity in hydrogenation reactions. This may provide an advantage because the reactions catalyzed by highly dispersed gold particles may be better controlled. In this work, TiO2 and SiO 2 supported Au catalysts were prepared by the deposition- precipitation method using urea and NaOH to precipitate the metallic component at different temperatures and hydrogen pressures. The metal loading for all the catalysts was 1 wt%. The catalysts were characterized by X-ray diffraction, high resolution transmission electron microscopy among others. The catalysts were then evaluated in the hydrogenation of nitrobenzene in a batch type reactor at 25 C. All the catalysts were active in the hydrogenation reaction and the major obtained product was aniline. © 2013 Springer Science+Business Media New York. Source

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