Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Susana Trasobares is active.

Publication


Featured researches published by Susana Trasobares.


Journal of the American Chemical Society | 2008

Comparative Structural and Chemical Studies of Ferritin Cores with Gradual Removal of their Iron Contents

Natividad Gálvez; Belén Fernández; Purificación Sánchez; Rafael Cuesta; Marcelo Ceolín; Miguel Clemente-León; Susana Trasobares; Miguel López-Haro; José J. Calvino; Odile Stéphan; José M. Domínguez-Vera

Transmission Electron Microscopy (TEM), X-ray Absorption Near Edge Spectroscopy (XANES), Electron Energy-Loss Spectroscopy (EELS), Small-Angle X-ray Scattering (SAXS), and SQUID magnetic studies were performed in a batch of horse spleen ferritins from which iron had been gradually removed, yielding samples containing 2200, 1200, 500, and 200 iron atoms. Taken together, findings obtained demonstrate that the ferritin iron core consists of a polyphasic structure (ferrihydrite, magnetite, hematite) and that the proportion of phases is modified by iron removal. Thus, the relative amount of magnetite in ferritin containing 2200 to 200 iron atoms rose steadily from approximately 20% to approximately 70% whereas the percentage of ferrihydrite fell from approximately 60% to approximately 20%. These results indicate a ferrihydrite-magnetite core-shell structure. It was also found that the magnetite in the ferritin iron core is not a source of free toxic ferrous iron, as previously believed. Therefore, the presence of magnetite in the ferritin cores of patients with Alzheimers disease is not a cause of their increased brain iron(II) concentration.


Angewandte Chemie | 2009

3 D Characterization of Gold Nanoparticles Supported on Heavy Metal Oxide Catalysts by HAADF‐STEM Electron Tomography

J. C. González; J. C. Hernández; Miguel López-Haro; E. del Río; Juan J. Delgado; Ana B. Hungría; Susana Trasobares; S. Bernal; Paul A. Midgley; José J. Calvino

Living on the edge: Three-dimensional reconstructions from electron tomography data recorded from Au/Ce(0.50)Tb(0.12)Zr(0.38)O(2-x) catalysts show that gold nanoparticles (see picture; yellow) are preferentially located on stepped facets and nanocrystal boundaries. An epitaxial relationship between the metal and support plays a key role in the structural stabilization of the gold nanoparticles.


Angewandte Chemie | 2010

Bridging the Gap between CO Adsorption Studies on Gold Model Surfaces and Supported Nanoparticles

Miguel López-Haro; Juan J. Delgado; José M. Cíes; Eloy del Río; S. Bernal; Robbie Burch; M.A. Cauqui; Susana Trasobares; J.A. Pérez-Omil; Pascale Bayle-Guillemaud; José J. Calvino

An in-depth understanding of CO adsorption on highly dispersed gold nanoparticles (AuNPs) is critically important to fully interpret the catalytic behavior of supported gold systems in processes such as CO oxidation, PROX (selective oxidation of CO in presence of a large excess of H2), [5–7] or LT-WGS (low-temperature water gas-shift) reactions. Despite its relevance, the quantitative data and fundamental information presently available on the CO–Au interaction mainly comes from studies carried out on model single-crystal and thin-film surfaces under experimental conditions far from those at which catalytic assays on supported gold systems are typically run. Probably because of the very weak and singular nature of the CO–Au interaction, which on the basis of both theoretical and experimental studies is generally acknowledged to take place on low-coordination surface sites, and the additional contribution of the support, a few studies have been carried out that were aimed at estimating the amount of CO adsorbed at low temperature on powdered or model supported AuNPs. To our knowledge, however, none of these have arrived at a detailed quantitative description of this process under conditions close to those occurring in real catalytic reactions. To bridge this gap, we have developed an approach in which AuNP size distributions, as determined from HAADFSTEM (high-angle annular dark-field scanning transmission electron microscopy) and quantitative CO adsorption data, as determined from volumetric adsorption at 308 K, under CO partial pressures ranging from 6.65 10 Pa to 3.99 10 Pa, are jointly analyzed with the help of a nanostructural model for the gold particles. This model could be deduced from the analysis of images recorded in a parallel HRTEM (highresolution transmission electron microscopy) study. As discussed herein, this approach gives a substantial experimental support to the extension to supported gold catalysts of the chemical principles governing the CO adsorption on model surfaces. We investigated two catalyst samples, 2.5 wt% Au/ Ce0.62Zr0.38O2 (Au/CZ) and 1.5 wt% Au/Ce0.50Tb0.12Zr0.38O2 x (Au/CTZ), which have significantly different gold particle size distributions. Two consecutive CO volumetric adsorption isotherms were recorded on the gold catalysts and the corresponding supports. Prior to running the second isotherms, samples were evacuated (residual pressure Pres< 1.33 10 4 Pa) for 30 min at 308 K. By processing the volumetric data in a similar way to earlier studies (for details, see the Supporting Information), the amounts of CO adsorbed on the AuNPs, on the surface cations of the supports (weak adsorption), and on the surface anions of the supports, which mainly consist of strongly chemisorbed carbonate species, could be determined from the difference of the two isotherms. The amount of CO adsorbed on the AuNPs at PCO= 1.33 10 4 Pa (100 Torr) was used as a measurement of the saturation coverage. The corresponding data are reported in Table 1 and the Supporting Information, Figure S1. Gold particle size distributions were determined for each of the investigated catalysts from the analysis of series of experimental ultra-high-resolution HAADF-STEM images (Supporting Information, Figure S2). In accordance with the physical principles lying behind the mechanism of image formation, this technique is particularly suitable for obtaining reliable metal particle size distributions in oxide-supported metal catalysts. Moreover, as recently shown, this technique can be fruitfully applied to a very fine characterization of AuNPs dispersed on mixed oxides of heavy elements, as is the case of those investigated herein. (Size distributions for Au/CZ and Au/CTZ catalysts are shown in the Supporting Information, Figure S2). [*] M. L pez-Haro, Dr. J. J. Delgado, J. M. Cies, E. del Rio, S. Bernal, Dr. M. A. Cauqui, Dr. S. Trasobares, Dr. J. A. P rez-Omil, Dr. J. J. Calvino Departamento de Ciencia de los Materiales e Ingenier a Metalfflrgica y Qu mica Inorg nica Facultad de Ciencias, Universidad de C diz Campus Rio San Pedro, 11510-Puerto Real, C diz (Spain) Fax: (+34)956-016-288 E-mail: [email protected]


Angewandte Chemie | 2011

Chemical Imaging at Atomic Resolution as a Technique To Refine the Local Structure of Nanocrystals

Susana Trasobares; Miguel López-Haro; Mathieu Kociak; Katia March; Francisco de La Peña; J.A. Pérez-Omil; José J. Calvino; N.R. Lugg; A.J. D'Alfonso; L. J. Allen; C. Colliex

The challenging problem of mapping the chemical composition of cation columns in individual nanocrystals at atomic resolution is addressed by using a method based on aberration-corrected electron microscopy, core-loss electron energyloss spectroscopy, and simulations. The potential of this novel approach to provide unique structural information, which is the key to rationalizing macroscopic behavior, is illustrated with the analysis of ceria–zirconia mixed oxides, which are nanomaterials with substantial technological impact. Metal nanoparticles supported on this family of oxides are currently materials of interest as catalysts in a variety of chemical transformations in the area of environmental protection, such as low-temperature water-gas shift, selective oxidation of CO in the presence of large amounts of hydrogen, or three-way catalysis. Strong variations in the chemistry of ceria–zirconia mixed oxide catalysts have been observed after they have undergone redox cycles involving reduction treatments at high temperatures ( 1173 K) then oxidation at mild temperatures ( 823 K). In particular their reducibility is significantly enhanced after such aging treatments. Scanning transmission electron microscopy (STEM) techniques have provided crucial information to account for these changes in the redox behavior. High-resolution electron microscopy (HREM) combined with high-angle annular dark-field (HAADF) imaging and tomography have revealed the occurrence of a disorder–order transformation in the cationic sublattice of these oxides, which tend to rearrange into a distribution characteristic of the so called pyrochlore phase. This phase is an archetype structure for A2B2O7 (A= + 3 cation, B=+ 4 cation) compounds and can be considered a fluorite superstructure. The structural transformation takes place during the reduction step of the cycle, in which the fully reduced mixed oxide with Ce/Zr molar ratio 1:1 adopts the Ce2Zr2O7 stoichiometry. Nevertheless, HAADF studies have clearly shown that, in the case of ceria–zirconia mixed oxides, this cation-ordered arrangement is preserved even after full reoxidation, that is, in the oxide with Ce2Zr2O8 stoichiometry, whenever the oxidation temperature does not exceed 823 K. Electron-microscopy studies have also revealed another remarkable feature of the ceria–zirconia aged oxides with the pyrochlore-type cation sublattice: the occurrence of compositional heterogeneities at the nanometer scale. Taking these observations into account and also considering that the disorder–order transition may not be completed in the time scale and under the temperature conditions used in the redox-cycling treatments, the important question arises whether these heterogeneities are in fact occurring on a finer scale, that is, at the atomic level. Such heterogeneities, compatible with the HREM and HAADF observations, will strongly influence the details of the counterpart oxygen sublattice and, consequently, the chemical and catalytic response of these oxides. To date, the atomic-column by atomic-column compositional analysis of the oxidized pyrochlore required to justify such a possibility has not been accomplished. Herein, using the capabilities of an aberration-corrected Nion UltraSTEM microscope (operated at 100 kV) we not only provide the first direct chemical evidence of the cationic order present in the Ce2Zr2O8 oxidized pyrochlore but we also show how atomicresolution electron energy-loss spectroscopy (EELS) mapping, based on core–shell ionization, can be combined with EELS image simulation to detect quite subtle local deviations in the cation sublattice from the completely ordered structure. This information provides a much more accurate structural description of the active catalyst nanocrystals, which must be considered to model both their oxygen-exchange capabilities and, eventually, their catalytic performance. [*] Dr. S. Trasobares, Dr. M. L pez-Haro, Dr. J. A. Perez-Omil, Dr. J. J. Calvino Departamento de Ciencia de los Materiales e Ingenier a Metalfflrgica y Qu mica Inorg nica Facultad de Ciencias, Universidad de C diz Campus Rio San Pedro, 11510-Puerto Real, C diz (Spain) Fax: (+34)956-016286 E-mail: [email protected] Homepage: http://www.uca.es/tem-uca


ACS Nano | 2012

Imaging nanostructural modifications induced by electronic metal-support interaction effects at Au||cerium-based oxide nanointerfaces.

Miguel López-Haro; José M. Cíes; Susana Trasobares; J.A. Pérez-Omil; Juan J. Delgado; S. Bernal; Pascale Bayle-Guillemaud; Odile Stéphan; Kenta Yoshida; Edward D. Boyes; Pratibha L. Gai; José J. Calvino

A variety of advanced (scanning) transmission electron microscopy experiments, carried out in aberration-corrected equipment, provide direct evidence about subtle structural changes taking place at nanometer-sized Au||ceria oxide interfaces, which agrees with the occurrence of charge transfer effects between the reduced support and supported gold nanoparticles suggested by macroscopic techniques. Tighter binding of the gold nanoparticles onto the ceria oxide support when this is reduced is revealed by the structural analysis. This structural modification is accompanied by parallel deactivation of the CO chemisorption capacity of the gold nanoparticles, which is interpreted in exact quantitative terms as due to deactivation of the gold atoms at the perimeter of the Au||cerium oxide interface.


Inorganic Chemistry | 2010

A bioinspired approach to the synthesis of bimetallic CoNi nanoparticles.

Natividad Gálvez; Elsa Valero; Marcelo Ceolín; Susana Trasobares; Miguel López-Haro; José J. Calvino; José M. Domínguez-Vera

Bimetallic CoNi nanoparticles have been prepared within the apoferritin cavity. The protein shell controls size, prevents aggregation, and makes nanoparticles water-soluble. The CoNi series prepared in this way were structurally and magnetically characterized, the resulting magnetic properties varying accordingly with composition (Co(75)/Ni(25), Co(50)/Ni(50), Co(25)/Ni(75)). Co and Ni metals were associated in each nanoparticle, as demonstrated by high-angle annular dark field scanning electron microscopy and electron energy loss spectroscopy (EELS). After intentional oxidation, the CoNi nanoparticles were characterized by EELS, X-ray absorption near edge structure (XANES), and SQUID measurements to evaluate the importance of the oxidation on magnetic properties.


Chemistry: A European Journal | 2010

Contributions of Electron Microscopy to Understanding CO Adsorption on Powder Au/Ceria–Zirconia Catalysts

José M. Cíes; Juan J. Delgado; Miguel López-Haro; R. Pilasombat; J.A. Pérez-Omil; Susana Trasobares; S. Bernal; José J. Calvino

The influence of the highly dispersed gold phase on the CO-support interaction occurring in two 2.5 wt % Au/Ce(0.62)Zr(0.38)O(2) catalysts with medium (Au/CZ-MD) and high (Au/CZ-HD) metal dispersion is quantitatively assessed. For this purpose, we have followed an approach in which high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), computer modelling, volumetric adsorption and FTIR spectroscopy studies are combined. This approach has already been fruitfully applied to the investigation of the specific CO-metal adsorption in Au/ceria-zirconia catalysts. As deduced from the experimental studies reported herein, the presence of gold dramatically increases the amount of CO strongly chemisorbed on the support. Moreover, this amount is sensitive to the metal dispersion, thus suggesting the occurrence of a mechanism in which the CO molecules that are initially adsorbed on the gold nanoparticles are further transferred to the support by means of a spillover process. An annular model is proposed for the growth of the CO phase adsorbed on the ceria-zirconia mixed oxide in the presence of Au. By assuming this model, we have estimated the width of the annulus, Delta r, of the adsorbed CO grown around the Au nanoparticles in Au/CZ-MD and Au/CZ-HD catalysts. This value is found to be very close to Delta r approximately 2 nm in both cases, the coincidence lending some additional support to the model. To further confirm this proposal, we have investigated the influence of CO pre-adsorption on the D(2)-Au/CZ-MD interaction, at 298 K. As revealed by FTIR spectroscopy, the kinetics of the deuterium spillover is significantly disturbed by the pre-adsorbed CO, which is fully consistent with an annular model for the CO adsorption. We conclude from the global analysis of the results reported here and those already available on CO-Au adsorption that the appropriate combination of nanostructural, computer modelling and chemical techniques is a powerful tool allowing us to gain a comprehensive picture of the complex series of processes involved in the CO adsorption on this relevant family of gold catalysts.


Chemcatchem | 2011

Advanced Electron Microscopy Investigation of Ceria–Zirconia-Based Catalysts

Miguel López-Haro; J.A. Pérez-Omil; Juan C. Hernández-Garrido; Susana Trasobares; Ana B. Hungría; José M. Cíes; Paul A. Midgley; P. Bayle‐Guillemaud; A. Martínez‐Arias; S. Bernal; Juan J. Delgado; José J. Calvino

The potentials of advanced transmission and scanning transmission electron microscopy in nanostructural studies of ceria–zirconia mixed oxides are overviewed. The crystallographic criteria that allow us to discriminate the different CeO2–ZrO2 polymorphs and the nanocrystal size range within which they can be applied are discussed. The combined use of high resolution electron microscopy (HREM) and high‐angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) to detect disorder–order transitions in the cation sublattice of this family of oxides and the size limit down to which each of them can be used for that purpose are also analyzed. Criteria to discriminate, on the basis of HREM images, the oxygen arrangement of the so called κ‐Ce2Zr2O8 phase from that of an oxidized pyrochlore Ce2Zr2O8 phase are presented and applied to the interpretation of experimental HREM images. HAADF‐STEM tomography studies and detailed analysis of HAADF‐STEM images establish both the crystallographic and compositional features of the surfaces of the mixed oxides that give enhanced redox activity. These findings allow deeper understanding of the influence of different thermal ageing pretreatments on the redox behavior of this family of mixed oxides. Novel characterization data do evidence that this model does not only fruitfully apply to binary ceria–zirconia oxides but also to more complex ternary oxides containing terbium.


Microscopy and Microanalysis | 2012

Microstructural and Chemical Characterization of Nanostructured TiAlSiN Coatings with Nanoscale Resolution

V. Godinho; T.C. Rojas; Susana Trasobares; F. J. Ferrer; Marie-Paule Delplancke-Ogletree; A. Fernández

Nanoscale resolution electron microscopy analysis combined with ion beam assisted techniques are presented here, to give answers to full characterization of morphology, growth mode, phase formation, and compositional distribution in nanocomposite TiAlSiN coatings deposited under different energetic conditions. Samples were prepared by magnetron sputtering, and the effects of substrate temperature and bias were investigated. The nanocomposite microstructure was demonstrated by the formation of a face-centered cubic (Ti,Al)N phase, obtained by substitution of Al in the cubic titanium nitride (c-TiN) phase, and an amorphous matrix at the column boundary regions mainly composed of Si, N (and O for the samples with higher oxygen contents). Oxygen impurities, predicted as the principal responsible for the degradation of properties, were identified, particularly in nonbiased samples and confirmed to occupy preferentially nitrogen positions at the column boundaries, being mainly associated to silicon forming oxynitride phases. It has been found that the columnar growth mode is not the most adequate to improve mechanical properties. Only the combination of moderate bias and additional substrate heating was able to reduce the oxygen content and eliminate the columnar microstructure leading to the nanocomposite structure with higher hardness (>30 GPa).


Chemcatchem | 2015

Low‐Lanthanide‐Content CeO2/MgO Catalysts with Outstandingly Stable Oxygen Storage Capacities: An In‐Depth Structural Characterization by Advanced STEM Techniques

Miguel Tinoco; Juan J. Sanchez; M.P. Yeste; Miguel López-Haro; Susana Trasobares; Ana B. Hungría; Pascale Bayle-Guillemaud; Ginesa Blanco; José M. Pintado; José J. Calvino

A novel CeO2/MgO catalyst with low ceria loading has been synthesized. This catalyst showed unique redox properties compared with conventional high and low surface area CeO2. Advanced (scanning) transmission electron microscopy techniques revealed the presence of a variety of highly dispersed ceria nanostructures: isolated CeOx entities, CeO2 clusters, as well as fairly small (<5 nm) CeO2 nanoparticles. More interestingly, this CeO2/MgO catalyst showed outstanding stability in its redox response against high temperature aging treatments. Thus, after reduction in hydrogen at 950 °C and further oxidation at 500 °C, CeO2 reduction effects took still place at low temperatures, and no significant loss of oxygen storage capacity (OSC) was detected. Unique ceria‐bilayer nanostructures were found and characterized in the aged catalyst. Their peculiar structural and chemical properties seem to be responsible for the large improvement observed in the stability of the redox response.

Collaboration


Dive into the Susana Trasobares's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Researchain Logo
Decentralizing Knowledge