Oxygen-Nonstoichiometric YBaCo4O7+δ as a Catalyst in H2O2 Oxidation of Cyclohexene

Here we present oxygen-nonstoichiometric transition metal oxides as highly prominent candidates to catalyze the industrially important oxidation reactions of hydrocarbons when hydrogen peroxide is employed as an environmentally benign oxidant. The proof-of-concept data are revealed for the complex cobalt oxide, YBaCo4O7+δ (0 60 % conversion) than the commercial TiO2 catalyst (<20 %) even though its surface area was less than one tenth of that of TiO2. In the 7-h experiments with YBaCo4O7+δ, 100 % conversion of cyclohexene was achieved. Immersion calorimetry measurements showed that the high catalytic activity may be ascribed to the exceptional ability of YBaCo4O7+δ to dissociate H2O2 and release active oxygen to the oxidation reaction.This work was supported by Academy of Finland (No. 255562) and Generalitat Valenciana (PROMETEO/2009/002)

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)

Mesoporous materials for clean energy technologies

Alternative energy technologies are greatly hindered by significant limitations in materials science. From low activity to poor stability, and from mineral scarcity to high cost, the current materials are not able to cope with the significant challenges of clean energy technologies. However, recent advances in the preparation of nanomaterials, porous solids, and nanostructured solids are providing hope in the race for a better, cleaner energy production. The present contribution critically reviews the development and role of mesoporosity in a wide range of technologies, as this provides for critical improvements in accessibility, the dispersion of the active phase and a higher surface area. Relevant examples of the development of mesoporosity by a wide range of techniques are provided, including the preparation of hierarchical structures with pore systems in different scale ranges. Mesoporosity plays a significant role in catalysis, especially in the most challenging processes where bulky molecules, like those obtained from biomass or highly unreactive species, such as CO2 should be transformed into most valuable products. Furthermore, mesoporous materials also play a significant role as electrodes in fuel and solar cells and in thermoelectric devices, technologies which are benefiting from improved accessibility and a better dispersion of materials with controlled porosity.The authors wish to thank the Spanish MINECO (Project CTQ2011-28954-C02-01) for financial support. E.S. acknowledges financial support from UA (Project GRE12-39)

Assessment of CO2 adsorption capacity on activated carbons by a combination of batch and dynamic tests

In this work, batch and dynamic adsorption tests are coupled for an accurate evaluation of CO2 adsorption performance for three different activated carbons obtained from olives stones by chemical activation followed by physical activation with CO2 at varying times, i.e. 20, 40 and 60 h. Kinetic and thermodynamic CO2 adsorption tests from simulated flue-gas at different temperature and CO2 pressure are carried out both in batch (a manometric equipment operating with pure CO2) and dynamic (a lab-scale fixed-bed column operating with CO2/N2 mixture) conditions. The textural characterization of the activated carbon samples shows a direct dependence of both micropore and ultramicropore volume on the activation time, hence AC60 has the higher contribution. The adsorption tests conducted at 273 and 293 K showed that, when CO2 pressure is lower than 0.3 bar, the lower the activation time the higher CO2 adsorption capacity and a ranking ωeq(AC20)>ωeq(AC40)>ωeq(AC60) can be exactly defined when T= 293 K. This result can be likely ascribed to a narrower pore size distribution of the AC20 sample, whose smaller pores are more effective for CO2 capture at higher temperature and lower CO2 pressure, the latter representing operating conditions of major interest for decarbonation of a flue-gas effluent. Moreover, the experimental results obtained from dynamic tests confirm the results derived from the batch tests in terms of CO2 adsorption capacity. It is important to highlight that the adsorption of N2 on the synthesized AC samples can be considered negligible. Finally, the importance of a proper analysis of characterization data and adsorption experimental results is highlighted for a correct assessment of CO2 removal performances of activated carbons at different CO2 pressure and operating temperature

Non-porous reference carbon for N2 (77.4 K) and Ar (87.3 K) adsorption

A new non-porous carbon material from granular olive stones has been prepared to be used as a reference material for the characterization of the pore structure of activated carbons. The high precision adsorption isotherms of nitrogen at 77.4 K and argon at 87.3 K on the newly developed sample have been measured, providing the standard data for a more accurate comparative analysis to characterize disordered porous carbons using comparative methods such as t- and αS-methods.Financial support from a Strategic Japanese–Spanish Cooperative Program: Nanotechnologies and New Materials for Environmental Challenges (PLE2009-0052). K.K. was supported by Exotic Nanocarbons, Japan Regional Innovation Strategy Program by the Excellent, JST

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

High selectivity of TiC-CDC for CO2/N2 separation

A series of carbide-derived carbons (CDC) have been prepared starting from TiC and using different chlorine treatment temperatures (500–1200 °C). Contrary to N2 adsorption measurements at −196 °C, CO2 adsorption measurements at room temperature and high pressure (up to 1 MPa) together with immersion calorimetry measurements into dichloromethane suggest that the synthesized CDC exhibit a similar porous structure, in terms of narrow pore volume, independently of the temperature of the reactive extraction treatment used (samples synthesized below 1000 °C). Apparently, these carbide-derived carbons exhibit narrow constrictions were CO2 adsorption under standard conditions (0 °C and atmospheric pressure) is kinetically restricted. The same accounts for a slightly larger molecule as N2 at a lower adsorption temperature (−196 °C), i.e. textural parameters obtained from N2 adsorption measurements on CDC must be underestimated. Furthermore, here we show experimentally that nitrogen exhibits an unusual behavior, poor affinity, on these carbide-derived carbons. CH4 with a slightly larger diameter (0.39 nm) is able to partially access the inner porous structure whereas N2, with a slightly smaller diameter (0.36 nm), does not. Consequently, these CDC can be envisaged as excellent sorbent for selective CO2 capture in flue-gas streams.This work was supported by the National Science Centre under the Grant No. DEC–2011/01/N/ST5/05595. Rafał Janus wishes to thank the Foundation for Polish Science MPD Programme co-financed by the EU European Regional Development Fund for the financial support. The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract No. POIG.02.01.00-12-023/08)

Characterization of Carbon Molecular Sieve Membranes Supported on Ceramic Tubes

Carbon molecular sieve membranes have been analyzed in supported and unsupported configurations in this experimental study. The membranes were used to adsorb CO2, N2 and CH4, and their adsorption data were analyzed to establish differences in rate and capacity of adsorption between the two types of samples (supported and unsupported). Experimental results show an important effect of the support, which can be considered as an additional parameter to tailor pore size on these carbon membranes. Immersion calorimetry values were measured by immersing the membranes into liquids of different molecular dimensions (dichloromethane, benzene, n-hexane, 2,2-dimethylbutane). Similarities were found between adsorption and calorimetric analysis. The pore volume of the samples analyzed ranged from 0.016 to 0.263 cm3/g. The effect of the pyrolysis temperature, either 550 or 700 °C, under N2 atmosphere was also analyzed. Quantification of the pore-size distribution of the support was done by liquid-liquid displacement porosimetry. The composite membrane was used for CO2/CH4 separation before and after pore plugging was done. The ideal selectivity factors value (4.47) was over the Knudsen theoretical factor (0.60) for membrane pyrolyzed at 600 °C, which indicates the potential application of these membranes for the separation of low-molecular weight gases.The authors are indebted to the Spanish Government for financial support (Project CTQ2008-02491, partially funded by the FEDER program of the European Union) and to the commission of European Communities Specific OpenTok Project MTKD-LT-2005-030040

Chemically activated poly(furfuryl alcohol)-derived CMK-3 carbon catalysts for the oxidative dehydrogenation of ethylbenzene

The surface of CMK-3 carbon, synthesized by the reversible replication of mesoporous silica (SBA-15) using poly(furfuryl alcohol) as a carbon precursor, was activated by wet oxidation with an aqueous solution of HNO3 or H2O2. The process was performed at 50 °C using solution containing different concentrations of the oxidizing agent. It was found that during the modification no significant changes in textural and structural properties of CMK-3 replica occurred. However, the treatment resulted in the formation of appreciable amounts of surface species containing oxygen. XPS and DRIFT spectroscopy allowed to identify and quantify the surface functional groups. Their stability was studied by TG-FTIR measurements. CO and CO2 were found as main gaseous products evolved during thermal decomposition under inert atmosphere. Finally, the modified samples were tested in the catalytic oxidative dehydrogenation of ethylbenzene to styrene at 350 °C in the presence of oxygen as an oxidizing agent (at O2/ethylbenzene molar ratio of 1.0 and 3.0). At the beginning of the catalytic run, the highest styrene yield and selectivity was achieved at the lower O2 content over the catalysts treated with nitric acid. Nevertheless, all studied catalysts underwent a gradual deactivation due to coke formation and changes in the distribution of surface moieties.This work was supported by the Polish National Science Centre under the grant no. DEC–2011/01/N/ST5/05595. The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program(contract No. POIG.02.01.00-12-023/08)