Time filter

Source Type

Leon V.,University of Castilla - La Mancha | Gonzalez-Dominguez J.M.,University of Castilla - La Mancha | Fierro J.L.G.,Institute Catalisis y Petroleoquimica ICP CSIC | Prato M.,University of Trieste | And 3 more authors.
Nanoscale | Year: 2016

The preparation of graphene suspensions in water, without detergents or any other additives is achieved using freeze-dried graphene powders, produced by mechanochemical exfoliation of graphite. These powders of graphene can be safely stored or shipped, and promptly dissolved in aqueous media. The suspensions are relatively stable in terms of time, with a maximum loss of ∼25% of the initial concentration at 2 h. This work provides an easy and general access to aqueous graphene suspensions of chemically non-modified graphene samples, an otherwise (almost) impossible task to achieve by other means. A detailed study of the stability of the relative dispersions is also reported. © 2016 The Royal Society of Chemistry.

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 | Year: 2013

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.

Mateos-Gil P.,Autonomous University of Madrid | Marquez I.,Institute Catalisis y Petroleoquimica ICP CSIC | Lopez-Navajas P.,CSIC - Biological Research Center | Jimenez M.,CSIC - Biological Research Center | And 5 more authors.
Biochimica et Biophysica Acta - Biomembranes | Year: 2012

Bacteria divide by forming a contractile ring around their midcell region. FtsZ, a cytoskeletal soluble protein structurally related to tubulin, is the main component of this division machinery. It forms filaments that bundle at the inner side of the cytoplasmic membrane. These FtsZ bundles do not attach to bare lipid surfaces. In Escherichia coli they remain near the membrane surface by attaching to the membrane protein ZipA and FtsA. In order to study the structure and dynamics of the ZipA-FtsZ bundles formed on a lipid surface, we have oriented a soluble form of ZipA (sZipA), with its transmembrane domain substituted by a histidine tag, on supported lipid membranes. Atomic force microscopy has been used to visualize the polymers formed on top of this biomimetic surface. In the presence of GTP, when sZipA is present, FtsZ polymers restructure forming higher order structures. The lipid composition of the underlying membrane affects the aggregation kinetics and the shape of the structures formed. On the negatively charged E. coli lipid membranes, filaments condense from initially disperse material to form a network that is more dynamic and flexible than the one formed on phosphatidyl choline bilayers. These FtsZ-ZipA filament bundles are interconnected, retain their capacity to dynamically restructure, to fragment, to anneal and to condense laterally. © 2011 Elsevier B.V. All rights reserved.

Lustemberg P.G.,CONICET | Bosco M.V.,CONICET | Bonivardi A.,CONICET | Busnengo H.F.,CONICET | Ganduglia-Pirovano M.V.,Institute Catalisis y Petroleoquimica ICP CSIC
Journal of Physical Chemistry C | Year: 2015

Formation of formate species on oxide surfaces plays a role in reactions for hydrogen production such as the water-gas shift and the steam-reforming of alcohols. It has been suggested that bridge formates are the most common and stable configuration on metal oxides. Ceria-based catalysts are important for these reactions where ceria is a "non-innocent" support. In this work, the nature of the formate species that are formed during decomposition and reaction of methanol on ceria surfaces have been studied using a combination of infrared temperature-programmed surface reaction (TPSR-IR) on a real powder catalyst support and density functional theory (DFT) together with statistical thermodynamics for model CeO2(111) surfaces. The influence of surface oxygen vacancies, hydroxyl groups, and water has been considered. Three different formate species have been identified (450-550 K). Initially, formates are adsorbed on the oxidized surface that is gradually hydroxylated by the release of hydrogen from methoxy groups (>500 K), which leads to a partially reduced surface. On the former, one kind of species is observed, whereas on the latter, the other two kinds appeared. We provide computational evidence that the bonding is only initially of the bridge type but becomes of the monodentate type as the surface concentration of hydroxyl groups rises. The calculated frequencies of the O-C-O symmetric and asymmetric stretching modes for the three structures are in good agreement with those experimentally observed. The existence of monodentate species is discussed in terms of a stabilizing effect of hydrogen bonds. The combined experimental and theoretical results on real and model systems, respectively, thus provide important insights on the reaction of methanol on ceria surfaces. © 2015 American Chemical Society.

Campos C.,University of Concepción | Torres C.,University of Concepción | Oportus M.,University of Concepción | Pena M.A.,Institute Catalisis y Petroleoquimica ICP CSIC | And 2 more authors.
Catalysis Today | Year: 2013

This study is based on 1%Ir/ZrO2 catalyst which was studied in the hydrogenation of aromatic meta-substituted nitrobenzene in liquid phase. The catalyst was prepared by traditional impregnation method using IrCl3 and it has been characterized in terms of temperature-programmed reduction (TPR), ICP-MS, BET area, X-ray diffraction, HR-TEM and XPS measurements. The hydrogenation was evaluated in a batch type reactor at 298 K using ethanol like a solvent. The catalyst showed the formation of zero valent and partially oxidized Iridium (Irδ+) is established post-TPR and XPS characterization. The metal particle size exhibited a wide distribution with mean size 1.8 nm. Ir/ZrO2 was active in all the hydrogenation reactions with elevated conversion and promoted exclusive NO2 group reduction, resulting in the sole formation of the corresponding amino-compound except for CHO and CHCH2 meta-substituted nitrobenzene. We associate this response to a reducible group competition between NO2 and CHO or CHCH2. Reactant activation on the catalyst generates a negatively charged intermediate, consistent with a nucleophilic mechanism. The presence of electron-donating substituents is shown to decrease NO2 reduction rate. This effect is quantified in terms of the Hammett relationship where a linear correlation between the substituent constant (σi) and rate is established and a reaction constant (ρ) 0.639. The data generated provide the first report of the catalytic action of supported Ir in the hydrogenation of meta-substituted nitroarenes and establish the nature of the hydrogenation en liquid phase. © 2013 Elsevier B.V. All rights reserved.

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 | Year: 2012

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.

Torres C.C.,University of Concepción | Alderete J.B.,University of Concepción | Mella C.,University of Concepción | Pawelec B.,Institute Catalisis y Petroleoquimica ICP CSIC
Journal of Molecular Catalysis A: Chemical | Year: 2016

Catalytic hydrogenation of maleic anhydride for the production of succinic anhydride can be a viable alternative to the higher energetic demand route based in the dehydration of succinic acid. In this sense, the metallic Ni catalysts supported on mesoporous TiO2 (anatase) substrate demonstrated to be very active and 100% selective in the liquid phase hydrogenation of maleic anhydride (MA) to succinic anhydride (SA). The catalysts, which were prepared via wet impregnation method with different Ni loading (5, 10 and 15 wt.%), were characterized by chemical analysis (ICP-AES), N2 physical adsorption-​desorption, H2-​temperature programmed reduction (H2-​TPR)​, X-ray diffraction (XRD)​, high resolution transmission electron spectroscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The Ni species interaction with support was investigated by TPR and by performing five catalyst recycling tests. After catalyst activation by reduction, the increase of Ni particle size with an increase of Ni loading was relatively small (from 6.9 to 8.9 nm) due to enhance of the metal-support interaction. After the first catalytic cycle, the optimized 5%Ni/TiO2 catalyst showed a small decrease in the Ni loading attributed to metal leaching during time course of reaction. Besides this, the 5%Ni/TiO2 catalyst exhibited a good stability during five continuous cycles with a very high yield of SA after 5 cycles. Finally, temperature experiments performed for the best system shown that the reaction temperature does not affect the SA selectivity in the temperature range studied (323 K–398 K). © 2016 Elsevier B.V.

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 | Year: 2016

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.

Torres C.,University of Concepción | Campos C.,University of Concepción | Fierro J.L.G.,Institute Catalisis y Petroleoquimica ICP CSIC | Oportus M.,University of Concepción | Reyes P.,University of Concepción
Catalysis Letters | Year: 2013

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.

PubMed | Institute Catalisis y Petroleoquimica ICP CSIC, University of Crete and Institute of Molecular Biology & Biotechnology
Type: Journal Article | Journal: Chemical communications (Cambridge, England) | Year: 2016

The sensitivity of QCM-D to molecular hydrodynamic properties is applied in this work to study conformational changes of the intrinsically disordered protein ZipA. Acoustic measurements can clearly follow ZipAs unstructured domain expansion and contraction with salt content and be correlated with changes in the hydrodynamic radius of 1.8 nm or less.

Loading Institute Catalisis y Petroleoquimica ICP CSIC collaborators
Loading Institute Catalisis y Petroleoquimica ICP CSIC collaborators