Síntesi catalítica de nanofibres de carboni a baixa temperatura

La finalitat d'aquest projecte és l'adquisició d'un nou coneixement científic i tecnològic que permeti desenvolupar nous materials a partir de la producció de nanofibres de carboni, que responguin a necessitats de diferents sectors tecnològics i millorin les propietats mecàniques, elèctriques i tèrmiques dels materials existents. En tant això, l'objectiu d'aquest projecte és obtenir una sèrie de mostres de diferents nanofibres de carboni amb propietats controlades. Aquestes estaran generades a partir de diferents paràmetres, com són la temperatura, el temps, el tipus de catalitzador, el tipus de preparació d'aquest i l'aplicació d'un camp magnètic. Un altre dels objectius és realitzar una purificació de les mostres obtingudes. Com també crear diferents compòsits a partir d'una matriu polimèrica termoplàstica d'acrilonitril butadiè estirè (ABS) i nanofibres de carboni, tant purificades com sense purificar, per finalment estudiar les conductivitats elèctriques i tèrmiques dels compòsits elaborats. En aquest estudi s'han emprat materials accessibles comercialment, amb la finalitat d'agilitzar la fase experimental i aconseguir sistemes més fàcilment reproduïbles

FIB/FESEM experimental and analytical assessment of R-curve behavior of WC-Co cemented carbides

Exceptional fracture toughness levels exhibited by WC-Co cemented carbides (hardmetals) are due mainly to toughening derived from plastic stretching of crack-bridging ductile enclaves. This takes place due to the development of a multiligament zone at the wake of cracks growing in a stable manner. As a result, hardmetals exhibit crack growth resistance (R-curve) behavior. In this work, the toughening mechanics and mechanisms of these materials are investigated by combining experimental and analytical approaches. Focused Ion Beam technique (FIB) and Field-Emission Scanning Electron Microscopy ( FESEM) are implemented to obtain serial sectioning and imaging of crack-microstructure interaction in cracks arrested after stable extension under monotonic loading. The micrographs obtained provide experimental proof of the developing multiligament zone, including failure micromechanisms within individual bridging ligaments. Analytical assessment of the multiligament zone is then conducted on the basis of experimental information attained from FIB/FESEM images, and a model for the description of R-curve behavior of hardmetals is proposed. It was found that, due to the large stresses supported by the highly constrained and strongly bonded bridging ligaments, WC-Co cemented carbides exhibit quite steep but short R-curve behavior. Relevant strength and reliability attributes exhibited by hardmetals may then be rationalized on the basis of such toughening scenario.Ministerio de España de Economía y Competitividad (Grant MAT2012-34602)Industry-University program between Sandvik Hyperion and Universitat Politècnica de Cataluny

Enhanced photocatalytic degradation of methylene blue: Preparation of TiO2/reduced graphene oxide nanocomposites by direct sol-gel and hydrothermal methods

In this study, two different preparation methods of titanium dioxide nanoparticles/reduced graphene oxide nanocomposites were investigated using direct sol-gel method followed by hydrothermal treatment or simple hydrothermal route. A different amount of graphene (1- 20%) was mixed with TiO2 for both series of samples in order to improve the photocatalytic activity. The influence of the preparation method on the physico-chemical properties was established by different characterization methods and the photocatalytic degradation of methylene blue (MB) under UV light irradiation was used as test reaction. The highest photocatalytic activity was observed for the nanocomposites containing 10 wt% of graphene. The elimination of MB can reach 93% and 82% for the nanocomposites with 10 wt% graphene prepared by the sol-gel and hydrothermal methods, respectively. These photocatalysts are promising for practical application in nanotechnology.Postprint (author's final draft

The influence of nano-architectured CeOx supports in RhPd/CeO2 for the catalytic ethanol steam reforming reaction

The ethanol steam reforming (ESR) reaction has been tested over RhPd supported on polycrystalline ceria in comparison to structured supports composed of nanoshaped CeO2 cubes and CeO2 rods tailored toward the production of hydrogen. At 650-700 K the hydrogen yield follows the trend RhPd/CeO(2)cubes >RhPd/CeO2-rods >RhPd/CeO2-polycrystalline, whereas at temperatures higher than 800K the catalytic performance of all samples is similar and close to the thermodynamic equilibrium. The improved performance of RhPd/CeO2-cubes and RhPd/CeO2-rods for ESR at low temperature is mainly ascribed to higher water-gas shift activity and a strong interaction between the bimetallic-oxide support interaction. STEM analysis shows the existence of RhPd alloyed nanoparticles in all samples, with no apparent relationship between ESR performance and RhPd particle size. X-ray diffraction under operating conditions shows metal reorganization on {1 0 0} and {1 1 0} ceria crystallographic planes during catalyst activation and ESR, but not on {1 1 1} ceria crystallographic planes. The RhPd reconstructing and tuned activation over ceria nanocubes and nanorods is considered the main reason for better catalytic activity with respect to conventional catalysts based on polycrystalline ceria. (C) 2015 Elsevier B.V. All rights reserved.Postprint (author's final draft

Visible light-driven H2 production over highly dispersed Ruthenia on Rutile TiO2 nanorods

The immobilization of miniscule quantities of RuO2 (~0.1%) onto one-dimensional (1D) TiO2 nanorods (NRs) allows H2 evolution from water under visible light irradiation. Rod-like rutile TiO2 structures, exposing preferentially (110) surfaces, are shown to be critical for the deposition of RuO2 to enable photocatalytic activity in the visible region. The superior performance is rationalized on the basis of fundamental experimental studies and theoretical calculations, demonstrating that RuO2(110) grown as 1D nanowires on rutile TiO2(110), which occurs only at extremely low loads of RuO2, leads to the formation of a heterointerface that efficiently adsorbs visible light. The surface defects, band gap narrowing, visible photoresponse, and favorable upward band bending at the heterointerface drastically facilitate the transfer and separation of photogenerated charge carriers.Peer ReviewedPostprint (published version

Assessment of kinetic model for ceria oxidation for chemical-looping CO2 dissociation

Chemical looping technologies are identified as to have an excellent potential for CO2 capture and fuels synthesis. Oxygen carriers are the fundamental component of a chemical looping process, and the choice of stable and efficient carriers with fast redox kinetics is the key to the successful design of the process. Hence, understanding the reaction kinetics is of paramount importance for the selection of an appropriate oxygen carrier material. This work provides a method for kinetic model selection based on a statistical approach to identify the reaction mechanism. The study experimentally investigates the oxidation kinetics of CeO2-d by CO2 and applies a statistical method for the selection of the best-fitting kinetic model for the reaction. The kinetic study is performed in the temperature range of 700–1000¿°C with a CO2 concentration between 20 and 40¿vol% in the feed. The measured peak rates of CO production on ceria were influenced both by temperature and concentration of reactant. The total CO production was more influenced by the temperature than by CO2 concentration, with a maximum CO yield of 33.66¿ml/g at 1000¿°C and 40% CO2. The identification of the oxidation kinetic model is performed by fitting different reactions models to the measured reaction rates and statistically comparing them using the Residual sum of squares (RSS), Akaike information criterion (AICc) and the F-test for the selection of the best-fitting one. Models corresponding to the nucleation and grain growth reaction mechanism provided a good fit of the data, with the Sestak-Berggren (SB) model showing the best approximation of the measured rate of reaction with an evaluated activation energy of 79.1¿±¿6.5¿kJ/mol for the CO2 oxidation.Peer ReviewedPostprint (author's final draft

Preuves d’extensions flexurales dans l’avant-pays rifain : le bassin du Rharb-Mamora (Nord Maroc)

Le bassin du Rharb représente l’avant-pays de la Cordillère du Rif. La Mamora (nord du Maroc) correspond à la bordure méridionale de ce bassin entre les nappes pré-rifaines alpines au nord et la Meseta hercynienne au sud. La Mamora, largement couverte par des formations actuelles, l’analyse du potentiel des ressources naturelles, leur exploitation et leur gestion cohérente nécessitent une bonne connaissance des diverses formations et de leurs structures. L’analyse et l’interprétation de profils sismiques, de forages hydrogéologiques et pétroliers ont permis de préciser les structures majeures de la Mamora, largement recouvertes par des sédiments néogènes. La structure de cette région est contrôlée par des failles au moins hercyniennes, bien connues dans le substratum paléozoïque. Les deux grandes familles, NE-SW et NW-SE, ont contrôlé l’évolution paléogéographique (répartition des faciès et variations de la puissance des formations). La faille majeure dans cette région est la faille Kénitra – Sidi-Slimane (FK2S) [Zouhri et al., 2001]. Cette faille N110oE, à fort pendage N, est localisée au S du front de la nappe pré-rifaine dont l’amortissement est aveugle. Elle se traduit par un effondrement progressif vers le N. Il pourrait s’agir d’une réplique de la faille Rabat – Tiflet. La Mamora apparaît ainsi comme une charnière entre le Rharb subsident et la Meseta marocaine stable depuis le Mésozoïque

Magnetite-supported palladium single-atoms do not catalyse the hydrogenation of alkenes but small clusters do

The activity of supported noble metal catalysts strongly depends on the particle size. The ultimate small-size limit is the single-atom catalyst (SAC), which maximizes the catalytic efficiency in the majority of the examples. Here, we investigate the catalytic behavior of Pd SACs supported on magnetite nanoparticles and we unambiguously demonstrate that Pd SACs are absolutely inactive in the hydrogenation of various alkene substrates. Instead, Pd clusters of low atomicity exhibit outstanding catalytic performance.Postprint (author's final draft

Deep seafloor magnetic observations under GEOSTAR project

Performing good quality magnetic observations is not an easy task; making them in the extreme marine environment is even much more challenging. The European funded GEOSTAR project succeeded in reaching this difficult goal. After the shallow seawater test experiment performed in the Adriatic sea in 1998, the main aims of the GEOSTAR project were achieved two years later during the six-month deep seafloor mission in the Tyrrhenian sea at around 2 km depth. Details and results about the shallow seawater mission in the Adriatic sea were published in previous articles; this paper is concerned with the deep seafloor mission in the Tyrrhenian sea close to Ustica Island and presents some results related to the geomagnetic recordings

Identification of highly selective surface pathways for methane dry reforming using mechanochemical synthesis of Pd-CeO2

The methane dry reforming (DRM) reaction mechanism was explored via mechanochemically prepared Pd/CeO2 catalysts (PdAcCeO2M), which yield unique Pd–Ce interfaces, where PdAcCeO2M has a distinct reaction mechanism and higher reactivity for DRM relative to traditionally synthesized impregnated Pd/CeO2 (PdCeO2IW). In situ characterization and density functional theory calculations revealed that the enhanced chemistry of PdAcCeO2M can be attributed to the presence of a carbon-modified Pd0 and Ce4+/3+ surface arrangement, where distinct Pd–CO intermediate species and strong Pd–CeO2 interactions are activated and sustained exclusively under reaction conditions. This unique arrangement leads to highly selective and distinct surface reaction pathways that prefer the direct oxidation of CHx to CO, identified on PdAcCeO2M using isotope labeled diffuse reflectance infrared Fourier transform spectroscopy and highlighting linear Pd–CO species bound on metallic and C-modified Pd, leading to adsorbed HCOO [1595 cm–1] species as key DRM intermediates, stemming from associative CO2 reduction. The milled materials contrast strikingly with surface processes observed on IW samples (PdCeO2IW) where the competing reverse water gas shift reaction predominates.Peer ReviewedPostprint (published version