Synthesis of Graphitic Carbon Nanostructures from Sawdust and Their Application as Electrocatalyst Supports

We present a novel and facile synthetic method for fabricating graphitic carbon nanostructures (GCNs) from sawdust. This method is based on the use of catalysts (Fe or Ni) that allows the direct conversion of sawdust into highly graphitized carbon material. The following procedure was used to obtain these graphitic nanoparticles:  (a) impregnation of the sawdust particles with iron or nickel salts, (b) carbonization of the impregnated material at a temperature of 900 or 1000 °C, and (c) selective removal of the non-graphitized carbon (amorphous carbon) by an oxidant (KMnO4). The resulting carbon is made up of nanosized graphitic structures (i.e., nanocapsules, nanocoils, nanoribbons), which have a high crystallinity, as evidenced by TEM/SAED, XRD and Raman analysis. These GCNs were used as supports for platinum nanoparticles. Such prepared electrocatalysts show an electrocatalytical surface area close to 90 m2.g-1 Pt, and they present a similar or higher electrocatalytic activity toward methanol electrooxidation than the Pt/Vulcan electrocatalyst prepared in the same conditions.The financial support for this research work provided by the Spanish MCyT (MAT2005-00262, MAT2004-01479 and FEDER) is gratefully acknowledged.Peer reviewe

Consejos a un joven científico: conferencia de Pedro Miguel Echenique

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Una nueva ruta de detoxificación de estrés oxidativo neuronal confiere neuroprotección

Trabajo presentado al Ciclo de Charlas en Biomedicina del Centro de Investigaciones Biológicas (CIB-CSIC) celebrada el lunes 8 de octubre de 2018 en el salon de actos del centro.Peer Reviewe

Monolitos celulares cerámico-carbono como soportes de catalizadores de desnitrificación y adsorbentes

Tesis presentada en el Departamento de Ingeniería Química y Tecnología del Medio Ambiente de la Universidad de Oviedo. Julio de 2003[EN] A procedure to prepare carbon-ceramic cellular monoliths has been developed in this work. Optimisation of preparation conditions has been carried out so that materials with a homogeneous carbon distribution and a high pore volume in the micropore range have been obtained. The composite monoliths have been analysed as catalyst supports and adsorbents in diluted gaseous streams. First of all, these carbon-ceramic monoliths have been used as catalysts support for manganese oxides and vanadium oxides in order to study their performance in the selective catalytic reduction (SCR) of nitrogen oxides with ammonia at low temperature (T<200ºC). The catalyst preparation procedure was optimised via tailoring the superficial properties of the carbonaceous support. The effect of different variables on catalytic activity and selectivity of the previously developed catalyst has been analysed. The catalysts developed here show a high catalytic activity, higher than that of other catalysts reported in literature. Vanadium-based catalysts are more resistant to SO2 deactivation than manganese-based catalysts. The presence of water vapour in the gas stream produces a decrease in catalytic activity for both types of catalysts. The initial value of catalytic activity is recovered after removing water from the inlet stream. Vanadium-based catalysts have been kept in the exit duct of a power plant in order to analyse their long-term stability. An important deactivation is observed after ~200 days in the power plant, mainly provoked by arsenic poisoning. An exhaustive analysis of the species involved in the low temperature SCR (125ºC) has been performed over manganese-based catalysts. A reaction mechanism has been developed from this analysis based on ammonia reaction from an adsorbed state with nitrogen dioxide from the gas phase (Eley Rideal type mechanism). Strong though partial deactivation of the catalyst is associated to formation of stable surface nitrates. Carbon-ceramic monoliths have also been proposed in this work as adsorbents of n-butane in diluted streams. In these conditions, the adsorption capacity of the monoliths developed here is higher than that of granular active carbon packed beds. Moreover, monoliths are easier to handle with and produce a lower pressure drop in the system than packed beds of active carbon granules. A model to predict the behaviour of carbon-ceramic monoliths in dynamic adsorption processes has also been developed. This model permits to obtain an excellent fitting of the experimental data by considering the existence of a gas velocity profile in the adsorption chamber.[ES] En este trabajo se ha desarrollado un procedimiento para la preparación de materiales celulares cerámico-carbono. Se han optimizado las condiciones de preparación de forma que se han obtenido materiales con una distribución homogénea de carbono y un desarrollo textural con un elevado volumen de poros en el rango de los microporos. Los monolitos compuestos preparados han sido analizados como soportes de catalizadores y adsorbentes en corrientes gaseosas diluidas. En primer lugar, los monolitos cerámicocarbono han sido utilizados como soporte de óxidos de manganeso y óxidos de vanadio con el objeto de analizar su comportamiento en el proceso de reducción catalítica selectiva (SCR) de óxidos de nitrógeno con amoniaco a baja temperatura (T<200ºC). Se han analizado los parámetros de preparación de los catalizadores, para lo cual se ha estudiado el efecto de diversos tratamientos que modifican las propiedades de la superficie carbonosa. Una vez optimizado el procedimiento de preparación de los catalizadores de óxidos de manganeso y óxidos de vanadio se analizó el efecto de distintas variables sobre la actividad catalítica y la selectividad de los catalizadores. Los catalizadores desarrollados en este trabajo muestran una elevada actividad catalítica, superior a la que presentan otros catalizadores propuestos en la literatura. Los catalizadores de óxidos de vanadio son más resistentes a la desactivación por SO2 que los catalizadores de óxidos de manganeso. La presencia de vapor de agua produce una disminución de la actividad catalítica de ambos catalizadores, aunque se recupera el valor inicial al retirar el agua de la corriente de entrada. Para analizar la estabilidad de los catalizadores en condiciones reales de utilización se han introducido catalizadores de óxidos de vanadio en el conducto de salida de gases de la Central Térmica de Aboño. Estos catalizadores sufren una importante desactivación producida principalmente por envenenamiento con arsénico. Se han analizado exhaustivamente las especies involucradas en la reacción SCR a baja temperatura (125ºC) sobre catalizadores de óxidos de manganeso. De este análisis ha sido posible obtener un mecanismo de reacción a baja temperatura basado en un mecanismo de tipo Eley-Rideal en el que el amoniaco reacciona desde el estado adsorbido con dióxido de nitrógeno desde la fase gas. También se ha encontrado que el catalizador sufre una fuerte desactivación, aunque no total, como consecuencia de la formación de nitratos superficiales estables. Finalmente se propone en este trabajo la aplicación de los materiales cerámico-carbono como adsorbentes de n-butano en bajas concentraciones. Se ha comprobado que en estas condiciones la capacidad de adsorción es superior a la de los lechos de carbón activo, además de presentar los monolitos ventajas asociadas a la baja caída de presión que producen en el sistema así como a su facilidad de manejo. Además, se ha desarrollado un modelo para predecir el comportamiento de los monolitos cerámico-carbono en procesos de adsorción dinámica, que permite un excelente ajuste de los datos experimentales obtenidos si se considera la existencia de un perfil de velocidad de gas en el interior de la cámara de adsorción.Peer reviewe

Towards the hydrogen economy?

The never ending debate on energy supply for a cleaner environment, recently associated with the worldwide effort to decrease global CO2 emissions, has been revived by the steep increase in oil prices and the parallel controversy about the potential of nuclear energy, initiated in the mass media on the anniversary of the nuclear disaster of Chernobyl. Thus, now seems an appropriate time for the scientific community and energy producers to exchange their knowledge in this debate far away from the magic solutions provided by mass media prophets, in an attempt to arrive at realistic guidelines that may help society to understand the important issues involved in the move towards a cleaner energy system. In this essay a description of the potential paths that may make it possible to change from the current energy sources to a cleaner energy production system is provided, the main focus being placed on how the so-called hydrogen economy might eventually be implemented. The milestones that the international agencies expect to emerge during the transition will be described, taking into account the issues of hydrogen production, distribution, storage and use. Additionally, the potential exploitation of the different hydrogen sources, both renewable and non-renewable, will be evaluated taking into account their availability and the efficiency of the processes used to transform them into hydrogen.The authors wish to thank Dr. J.C. Abanades for his fruitful suggestions and comments to improve the quality of this work. TVS acknowledges CSIC-ESF for the award of an I3P postdoctoral contract. The financial support for this research provided by the Spanish MCyT (MAT2005-00262) and FICYT Regional Project (IB05-001) is gratefully acknowledged.Peer reviewe

High surface area stainless steel wire mesh-supported TiO2 prepared by sacrificial template accelerated hydrolysis. A monolithic photocatalyst superior to P25 TiO2

High surface area stainless steel wire mesh-supported TiO2 catalysts were prepared by sacrificial template accelerated hydrolysis using highly polar stainless steel wire mesh-supported ZnO templates. The monolithic catalysts were tested for the photodegradation of methylene blue in aqueous solution under ultraviolet irradiation. The calcination temperature of the catalysts was observed to have a determinant effect on their catalytic activity. The optimum calcination temperature range was 450–600 °C, in which a combination of high surface area (50–90 m2 g−1), a high degree of crystallinity and a minimum rutile content yielded the best catalytic results, with maximum catalytic activity appearing for a calcination temperature of 450 °C. The most active catalyst prepared in this work displayed twice the catalytic activity of the reference catalyst, P25 TiO2.The financial support for this research work provided by the Spanish MEC (CTQ2011-24776) is gratefully acknowledged. Tan T. Vu is grateful to the CSIC for the award of a JAE predoc grant.Peer reviewe

Novel high surface area stainless steel wire mesh supported Ni0.7Zn0.3O solid solution prepared by room temperature sacrificial template accelerated hydrolysis. Application in the production of hydrogen from methanol

This work describes for the first time the room-temperature synthesis of a high surface area Ni0.7Zn0.3O solid solution by sacrificial template accelerated hydrolysis. The synthesis employs a highly polar ZnO template supported on the surface of a stainless steel wire mesh (SSWM) that allows the material to be produced in a monolithic configuration. The resulting material has a large surface area of around 100 m2 g−1 and is obtained in a yield of up to 40 wt.% on the SSWM in the synthesis conditions employed in this work. Characterization of the material by TPR, XRD and XPS revealed that the solid solution is composed of an oxygen-defective bulk and a partially oxidized surface. As part of this study, the Ni0.7Zn0.3O solid solution has been tested for the first time as a catalyst, displaying high activity in both the methanol steam reforming and the methanol decomposition reactions. At temperatures below 400 °C the catalyst is not very selective in the methanol steam reforming reaction, and produces large amounts of CO. However, at more elevated temperatures the water gas shift reaction improves the hydrogen yield and the carbon selectivity towards CO2, especially over higher contact times. Despite some catalyst deactivation due to coke deposition, methanol decomposition occurs with high conversion degrees and hydrogen yields in the temperature range of 250–350 °C.The financial support for this research work provided by the Spanish MEC (CTQ2011-24776) is gratefully acknowledged. Tan T. Vu is grateful to the CSIC for the award of a JAE predoc grant.Peer reviewe

Nuevos formatos de divulgación científica en internet

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