9,832 research outputs found
A theoretical insight into the catalytic effect of a mixed-metal oxide at the nanometer level: The case of the highly active metal/CeOx/TiO2(110) catalysts
The structural and electronic properties of CeOx species supported on the rutile TiO2 110 surface
have been examined by means of periodic density-functional calculations that use a generalized
gradient approximation functional including a Hubbard-like type correction. Deposition of Ce atoms
leads in a first step to Ce3+ ions bound to the surface through bridge and in-plane oxygen atoms, the
released electrons occupying the Ti 3d empty orbitals. Further addition of Ce and molecular oxygen
gives place to Ce2O3 dimers diagonally arranged on the surface, in agreement with the spots
observed in the scanning tunnel microscope images. The formation process of CeOx nanoparticles
NPs on the TiO2 surface is highly exothermic and our calculations show that the redox properties
of the Ce III-Ce IV couple are significantly altered when it is supported on TiO2. In particular the
reactivity against CO/O2 indicates that on the surface the presence of Ce III is favored over Ce IV
species. Our results also indicate that the CeOx /TiO2 interface should be seen like a real
mixed-metal oxide rather than a supported NP of ceria. Finally, in the context of the high catalytic
activity of the M /CeOx /TiO2 M =Au,Cu,Pt systems in the water-gas shift reaction, we
have examined the dissociation of water on the CeOx /TiO2 surface and estimated a barrier as
small as 0.04 eV, i.e. 8 times smaller than that computed for a TiO2 oxygen vacancy. This result
agrees with the experimental superior catalytic activity of the M /CeOx /TiO2 systems over
M /TiO2.Gobierno de España. Ministerio Ciencia e Innovación (MICINN) MAT2005-01872 y CSD2008-0023Junta de Andalucía FQM-132Departamento de Energía de EE. UU. División de Subvención de Ciencias Químicas DE-AC02-98CH1088
Personal aircraft: a more affordable luxury
Access to luxury products has been limited traditionally to the upper classes. Products and services related to the means of transport have usually been considered of luxury and industrialization has made accessible to much of the population in developed countries. An emerging market is personal aircraft which is currently restricted to certain layers of society but it is expected that their use will represent the next great advance in transport. This article has the object of presenting the results of ongoing research and it focuses on possible demand and the tendency to use this transport option in Spanish societ
Interaction of oxygen with TiN (001): N↔O exchange and oxidation process
This work presents a detailed experimental and theoretical study of the oxidation of TiN(001) using a combination of synchrotron-based photoemission and density functional theory (DFT). Experimentally, the adsorption of O2 on TiN(001) was investigated at temperatures between 250 and 450K. At the lowest temperature, there was chemisorption of oxygen (O2,gas→2Oads) without significant surface oxidation. In contrast, at 450K the amount of O2 adsorbed increased continuously, there was no evidence for an oxygen saturation coverage, a clear signal in the Ti 2p core level spectra denoted the presence of TiOx species, and desorption of both N2 and NO was detected. The DFT calculations show that the adsorption/dissociation of O2 is highly exothermic on a TiN(001) substrate and is carried out mainly by the Ti centers. A high oxygen coverage (larger than 0.5 ML) may induce some structural reconstructions of the surface. The exchange of a surface N atom by an O adatom is a highly endothermic process (ΔE=2.84eV). However, the overall oxidation of the surface layer is thermodynamically favored due to the energy released by the dissociative adsorption of O2 and the formation of N2 or NO. Both experimental and theoretical results lead to conclude that a TiN+mO2→TiOx+NO reaction is an important exit channel for nitrogen in the oxidation process.Ministerio de Educación y Ciencia de España, MEC. MAT2005-01872Junta de Andalucía. FQM-132División de Ciencias Químicas del Departamento de Energía de EE. UU. DE-AC02-98CH10086Fundación japonesa para la Ciencia de los Materiale
Modulación de la expresión de citoquinas por cambios metabólicos y estrés de retículo endoplasmático
El sistema inmunitario se ha desarrollado a lo largo del proceso evolutivo para
combatir las infecciones y proteger al organismo frente a elementos que suponen una
amenaza para su integridad mediante una respuesta que permita la supervivencia. Por
este motivo, el sistema inmune es el encargado de mantener la homeostasis celular
mediante la eliminación del patógeno y reparación del daño causado.
Las células del sistema inmunitario tienen la cualidad de poder diferenciar lo propio de lo
extraño, “self non-self model” (1) sugerido por Burnet en los años 60 cuando trataba de
explicar la tolerancia inmune. Posteriormente, Janeway precisó con más acierto esta
cualidad al enunciar como principio funcional del sistema inmune la propiedad de
distinguir lo “Propio no infeccioso de lo infeccioso no propio”. Este concepto ha permitido
reconocer el papel de los patrones moleculares como elementos fundamentales en el
reconocimiento de los patógenos. Como una continuación de esta teoría del
reconocimiento por el sistema inmune, Matzinger P. sugirió el modelo de peligro “Danger
model” (2) que añade a la capacidad del organismo para discriminar lo potencialmente
peligroso mediante el reconocimiento de patógenos, la identificación de señales de alarma
procedentes de tejidos dañados.Máster en Investigación Biomédic
Improving the activity of gold nanoparticles for the water-gas shift reaction using TiO2–Y2O3: an example of catalyst design
In the last ten years, there has been an acceleration in the pace at which new catalysts for the watergas
shift reaction are designed and synthesized. Pt-based catalysts remain the best solution when only
activity is considered. However, cost, operation temperature, and deactivation phenomena are important
variables when these catalysts are scaled in industry. Here, a new catalyst, Au/TiO2–Y2O3, is presented
as an alternative to the less selective Pt/oxide systems. Experimental and theoretical techniques are
combined to design, synthesize, characterize and analyze the performance of this system. The mixed
oxide demonstrates a synergistic effect, improving the activity of the catalyst not only at large-to-medium
temperatures but also at low temperatures. This effect is related to the homogeneous dispersion of the
vacancies that act both as nucleation centers for smaller and more active gold nanoparticles and as
dissociation sites for water molecules. The calculated reaction path points to carboxyl formation as the
rate-limiting step with an activation energy of 6.9 kcal mol 1, which is in quantitative agreement with
experimental measurements and, to the best of our knowledge, it is the lowest activation energy
reported for the water-gas shift reaction. This discovery demonstrates the importance of combining
experimental and theoretical techniques to model and understand catalytic processes and opens the
door to new improvements to reduce the operating temperature and the deactivation of the catalyst.Ministerio de Economía y Competitividad (CTQ2015-64669-P and ENE2015-66975- C3-2-R)Junta de Andalucía (FQM-132 and TEP-106)European Union (HT-PHOTO-DB No. 752608
Propuesta de un modelo y factores determinantes de la fragmentación internacional de la producción en el sector automóvil de España
Una de los rasgos más característicos de la presente globalización es el desarrollo de la fragmentación de la producción, siendo esta, la división del proceso productivo en diferentes localizaciones a lo largo de varios países. Debido a la globalización de los mercados, al surgimiento de nuevas zonas económicas (Zona Euro, Nafta, Mercosur, etc.), a los países emergentes (China, India, Rusia, Brasil), a la reducción de los costes del transporte internacional y al desarrollo de las comunicaciones, ha provocado el incremento del comercio internacional en bienes intermedios, así como el diseño, fabricación y ensamblaje de un producto en diferentes localizaciones a lo largo de varios países. El incremento de la fragmentación en el comercio internacional ha creado un interés por saber cuales son los factores determinantes de la misma en bienes intermedios. El indicador IITV es el utilizado para medir la fragmentación de la producción entre España y sus 19 principales socios comerciales y varios factores sugeridos por la literatura en fragmentación son utilizados en un rango de años desde el año 2004 al año 2008. Los resultados obtenidos muestran que la gran mayoría del comercio en bienes intermedios es IITV y los factores determinantes de la fragmentación de la producción en el sector del automóvil en España, son el tamaño del mercado, la pertenencia a UE, la distancia y el coeficiente de libre comercio
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