Versatilidad de los materiales basados en carbono

La versatilidad de los materiales basados en el carbono se discute usando una serie de ejemplos extraídos de la experiencia de nuestro grupo de investigación a lo largo de los últimos cuarenta años. Adsorbentes como el carbón activado, tamices moleculares de carbón, etc. constituyen un buen ejemplo de esta versatilidad, no solo por la variedad de precursores y métodos de activación que se pueden usar en su fabricación, sino también por la flexibilidad en las formas físicas o las estructuras porosa y química, que son la base para la gran cantidad de aplicaciones; por esta razón el carbón activado es considerado como el adsorbente universal. La versatilidad es también notoria cuando algunos de estos materiales de carbón se utilizan en catálisis o en la síntesis/aplicación de carbones estructurales, materiales, compuestos, etc. Finalmente, la irrupción del grafeno y los nanotubos de carbón nos ha permitido ampliar la perspectiva de la versatilidad excepcional de los materiales de carbón.The versatility of carbon materials will be discussed using a series of examples taken from materials studied at our research group along the last forty years. Thus, carbon adsorbents (activated carbon, carbon molecular sieves, etc.) constitute a good example of this versatility, not only for the variety of precursors/activation methods that can be used in their manufacture, but also for the flexibility in their physical forms, or porous and chemical structure, that are the base for the very large number of applications; for these reasons activated carbon is known as the universal adsorbent. The versatility is also notorious in the use of some of these carbon materials in catalysis or in the synthesis/application of structural carbons, composites, etc. Today, nanotubes and graphene are being developed to widen further our appreciation of the unique versatility of carbon materials

A site energy distribution function for the characterization of the continuous distribution of binding sites for gases on a heterogeneous surface

A binding site energy distribution function for a Jensen-Seaton isotherm and its limiting cases was proposed and successfully applied to the adsorption of several gas molecules on different essentially microporous carbons. According to the proposed model the studied carbon materials exhibit two energetic states where the site energy is exponentially or unimodaly distributed depending on the adsorption pressure. Carbons with a larger contribution from micropores seem to be in general more heterogeneous, with a wider binding site energy distribution, than less microporous carbons.Support from the Ministerio de Ciencia e Innovacion (Project PLE2009-0052) and the Genaralitat Valenciana (Project PROMETEO/2009/002-FEDER) are acknowledged. KVK would like to thank the Ministerio de Ciencia e Innovacion for the Juan de la Cierva contract. ASA acknowledges a PhD fellowship from MEC, Spain

Effect of the presence of chlorine in bimetallic PtZn/CeO2 catalysts for the vapor-phase hydrogenation of crotonaldehyde

The effect of the reduction temperature has been studied on ceria-supported bimetallic platinum–zinc catalysts prepared from H2PtCl6 and Pt(NH3)4(NO3)2 as the platinum precursors and Zn(NO3)2 as the zinc precursor. The catalysts have been characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS), and their catalytic behavior has been evaluated in the vapor-phase hydrogenation of toluene and of crotonaldehyde (2-butenal) after reduction at low (473 K) and high (773 K) temperatures. The increase in the reduction temperature produces a strong decrease in the catalytic activity for toluene hydrogenation in both systems, but an important increase of activity for crotonaldehyde hydrogenation, which is more evident for the chlorine-free catalyst. The selectivity towards the hydrogenation of the carbonyl bond to yield the unsaturated alcohol (crotyl alcohol, 2-buten-1-ol) also increases after reduction at high temperature, being somewhat higher for the Cl-containing catalyst. The results are discussed in terms of differences in surface composition of the catalysts.C.I.C.Y.T. (Project BQU 2000-0467)

Retos actuales para la captura y almacenamiento de CO2

Las grandes emisiones de CO2 procedentes de la combustión de combustibles fósiles están provocando un calentamiento global en nuestro planeta. Estos problemas medioambientales están obligando a los diferentes gobiernos a buscar soluciones que permitan reducir esas emisiones y mitigar sus efectos adversos. Una de las soluciones más prometedoras consiste en la captura selectiva de CO2 en efluentes industriales mediante el uso de materiales adsorbentes porosos (zeolitas, carbón activado y materiales híbridos MOFs) que combinen una elevada capacidad de adsorción y una adecuada selectividad a CO2 frente al resto de gases del proceso industrial, además de una adecuada regeneración.Large CO2 emissions coming from the combustion of fossil fuels are responsible for the global warming in the Earth. These environmental concerns are forcing the different governments to find solutions to reduce CO2 emissions and mitigate these adverse effects. One of the most promising solutions consists in the selective CO2 capture on industrial streams using porous adsorbents (zeolites, activated carbons and MOFs) combining a high adsorption capacity and a proper selectivity to CO2 versus other molecules from flue gas, together with a proper regeneration

High-Resolution N2 Adsorption Isotherms at 77.4 K: Critical Effect of the He Used During Calibration

Accurate characterization of the microporous structure in porous solids is of paramount importance for several applications such as energy and gas storage, nanoconfinement reactions, and so on. Among the different techniques for precise textural characterization, high-precision gas adsorption measurement of probe molecules at cryogenic temperatures (e.g., N2 at 77.4 K and Ar at 87.3 K) is the most widely used, after appropriate calibration of the sample holder with a probe gas, which does not experience physisorption processes. Although traditionally helium has been considered not to be adsorbed in porous solids at cryogenic temperatures, here we show that even at 77.4 K (high above its boiling temperature, 4 K) the use of He in the calibration step can give rise to erroneous interpretations when narrow micropores/constrictions are present.Authors acknowledge financial support from the MICINN (project PLE2009-0052) and Generalitat Valenciana (PROMETEO/2009/002)

Effect of the porous structure in carbon materials for CO2 capture at atmospheric and high-pressure

Activated carbons prepared from petroleum pitch and using KOH as activating agent exhibit an excellent behavior in CO2 capture both at atmospheric (∼168 mg CO2/g at 298 K) and high pressure (∼1500 mg CO2/g at 298 K and 4.5 MPa). However, an exhaustive evaluation of the adsorption process shows that the optimum carbon structure, in terms of adsorption capacity, depends on the final application. Whereas narrow micropores (pores below 0.6 nm) govern the sorption behavior at 0.1 MPa, large micropores/small mesopores (pores below 2.0–3.0 nm) govern the sorption behavior at high pressure (4.5 MPa). Consequently, an optimum sorbent exhibiting a high working capacity for high pressure applications, e.g., pressure-swing adsorption units, will require a poorly-developed narrow microporous structure together with a highly-developed wide microporous and small mesoporous network. The appropriate design of the preparation conditions gives rise to carbon materials with an extremely high delivery capacity ∼1388 mg CO2/g between 4.5 MPa and 0.1 MPa. Consequently, this study provides guidelines for the design of carbon materials with an improved ability to remove carbon dioxide from the environment at atmospheric and high pressure.Financial support from MINECO: Strategic Japanese-Spanish Cooperative Program (PLE2009-0052) and Generalitat Valenciana (PROMETEO/2009/002)

Free-standing compact cathodes for high volumetric and gravimetric capacity Li–S batteries

Free-standing high performance Li–S battery cathodes are currently attracting significant research efforts. Loose macroporous structures have been proposed by many to improve sulfur utilization and areal capacity. However, their low cathode sulfur densities and high electrolyte fractions lead to low cell volumetric and gravimetric capacities. We report here a compact free-standing Li–S cathode structure that delivers areal, volumetric and gravimetric capacities all exceeding those of typical Li-ion batteries. The cathodes, formed by pressure filtration of the constituents, are composed of highly micro/mesoporous nitrogen-doped carbon nanospheres (NCNSs) embedded in the macropores of a multi-walled carbon nanotube (MWCNT) network to form a dense structure. The MWCNT network facilitates low cathode impedance. The NCNSs maximize sulfur utilization and immobilization. These collectively result in high cathode volumetric capacity (1106 mA h cm−3) and low electrolyte requirement (6 μL mg−1 of sulfur), which together lead to high cell-level gravimetric capacity. Stable long-term cycling at 0.3C (2.5 mA cm−2 for 5 mg cm−2 areal sulfur-loading) has also been achieved, with the areal and volumetric capacities of the best remaining above typical Li-ion values over 270 cycles and the per-cycle capacity fading being only 0.1%. The facile preparation means significant potential for large scale use.CH acknowledges a Postdoctoral Fellowship provided by Loughborough University

Water adsorption in hydrophilic zeolites: experiment and simulation

We have measured experimental adsorption isotherms of water in zeolite LTA4A, and studied the regeneration process by performing subsequent adsorption cycles after degassing at different temperatures. We observed incomplete desorption at low temperatures, and cation rearrangement at successive adsorption cycles. We also developed a new molecular simulation force field able to reproduce experimental adsorption isotherms in the range of temperatures between 273 K and 374 K. Small deviations observed at high pressures are attributed to the change in the water dipole moment at high loadings. The force field correctly describes the preferential adsorption sites of water at different pressures. We tested the influence of the zeolite structure, framework flexibility, and cation mobility when considering adsorption and diffusion of water. Finally, we performed checks on force field transferability between different hydrophilic zeolite types, concluding that classical, non-polarizable water force fields are not transferable.The European Research Council through an ERC Staring Grant (Sofia Calero), and the MICINN (CTQ2010-16077) project

Very high methane uptake on activated carbons prepared from mesophase pitch: A compromise between microporosity and bulk density

Two petroleum residues were pyrolyzed under two different conditions to obtain pitches with low or high mesophase content. The effect of the KOH: precursor ratio and the activation temperature on the packing density and porous texture of the carbons have been studied and optimized. Activated carbons combining high micropore volume (>1 cm3/g) and high packing density (0.7 g/cm3) have been successfully prepared. Regarding excess methane adsorption capacities, the best results (160 cm3 (STP)/cm3 at 25 °C and 3.5 MPa) were obtained using the pitch with the higher content of the more organized mesophase, activated at relatively low temperature (700 °C), with a medium KOH: precursor ratio (3:1). Some of the activated carbons exhibit enhanced adsorption capacity at high pressure, giving values as high as 175 cm3 (STP)/cm3 at 25 °C and 5 MPa and 200 cm3 (STP)/cm3 at 25 °C and 10 MPa (the same amount as in an empty cylinder but at half of the pressure), indicating a contribution of large micropores and narrow mesopores to adsorption at high pressure. The density of methane in pores between 1 and 2.5 nm at pressure up to 10 MPa was estimated to understand their contribution to the total adsorption capacity.Authors acknowledge financial support from MINECO: Project MAT2013-45008-p and CONCERT Project-NASEMS (PCIN-2013-057) and Generalitat Valenciana (PROMETEO/2009/002)

Neumonía por virus influenza A (H1N1) y su evolución atípica en la Unidad de Cuidados Intensivos

It is presented a patient of 50 years old, atypical in its evolution and its complications, he was hospitalized in February 2014 in the Intensive Care Unit of the  "Arnaldo Milian Castro"Surgical Hospital, City of Santa Clara, Villa Clara Province. He presented fever, dry cough, arthralgia, myalgia, and dyspnea. He was diagnosed with community-acquired pneumonia caused by influenza A virus (H1N1) to test -confirmed chain reaction reversa- transcriptase-polymerase; he had an unusual evolution, with complications such as spontaneous pneumothorax right, necrotizing pneumonia and empyema caused by Pseudomonas of the same side. The patient progressed satisfactorily despite the complications and was discharged at 30 days.Se presenta un paciente de 50 años, atípico por su evolución y sus complicaciones, hospitalizado en febrero de 2014 en la Unidad de Cuidados Intensivos del Hospital Clínico Quirúrgico “Arnaldo Milián Castro”, de la Ciudad de Santa Clara, Provincia de Villa Clara, por presentar fiebre, tos seca, artralgia, mialgia y disnea. Se le diagnosticó neumonía adquirida en la comunidad causada por el virus de influenza A (H1N1) -confirmado con la prueba de reacción en cadena de la polimerasa-transcriptasa reversa-; tuvo una evolución poco común, con complicaciones como neumotórax espontáneo derecho, neumonía necrotizante y empiema por pseudomona de ese mismo hemitórax. El paciente evolucionó satisfactoriamente pese a las complicaciones y fue egresado a los 30 días