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Manzanares M.,Catalonia Institute for Energy Research IREC | Fabrega C.,Catalonia Institute for Energy Research IREC | Oriol Osso J.,Research Center | Oriol Osso J.,Air Products Group | And 5 more authors.
Applied Catalysis B: Environmental | Year: 2014

Magnesium modified TiO2 photocatalyst has been found to improve the CO2 photoreduction reaction, with a high selectivity towards CH4. Thus, Mg-TiO2 has been synthesized with different compositions up to 2.0wt%. Unlike the bare TiO2, the surface reorganization originated by the presence of Mg enhances the formation of methane by a factor of 4.5, corroborating that complete reduction of CO2 is achieved. It was found that the enhancement of the overall photocatalytic activity towards carbon dioxide reduction can be increased by a factor of 3, revealing a straightforward correlation with the surface states induced by the presence of the doping element. Finally, the evolution of the selectivity versus methane formation against hydrogen is discussed for the different magnesium loadings. © 2013 Elsevier B.V.


Llovell F.,Research Center | Llovell F.,CSIC - Institute of Materials Science | Marcos R.M.,Rovira i Virgili University | MacDowell N.,Research Center | And 3 more authors.
Journal of Physical Chemistry B | Year: 2012

In this work, the solubility of three common pollutants, SO2, NH3, and H2S, in ionic liquids (ILs) is studied using the soft-SAFT equation of state with relatively simple models. Three types of imidazolium ionic liquids with different anions are described in a transferable manner using the recently published molecular models (Andreu, J. S.; Vega, L. F. J. Phys. Chem. C2007, 111, 16028; Llovell et al. J. Phys. Chem. B2011, 115, 4387), whereas new models for SO2, NH3, and H2S are proposed here. Alkyl-imidazolium ionic liquids with the [PF 6]- and [BF4]- anions are considered to be Lennard-Jones chainlike molecules with one associating site in each molecule describing the specific cation-anion interactions. Conversely, the cation and anion forming the imidazolium [Tf2N]- ionic liquids are modeled as a single molecule with three associating sites, taking into account the delocalization of the anion electric charge due to the presence of oxygen groups surrounding the nitrogen of the anion. NH3 is described with four associating sites: three sites of type H mimicking the hydrogen atoms and one site of type e representing the lone pair of electrons. H2S is modeled with three associating sites: two for the sites of type H for the hydrogen atoms and one site of type e for the electronegativity of the sulfur. SO2 is modeled with two sites, representing the dipole moment of the molecule as an associative interaction. Soft-SAFT calculations with the three models for the pollutants provide very good agreement with the available phase equilibria, enthalpy of vaporization, and heat capacity experimental data. Then, binary mixtures of these compounds with imidazolium-based ionic liquids were calculated in an industrially relevant temperature range. Unlike association interactions between the ionic liquids and the pollutant gases have been explicitly accounted for using an advanced association scheme. A single temperature independent energy binary parameter is sufficient to describe every family of mixtures in good agreement with the available data in the literature. In addition, a vapor-liquid-liquid equilibrium (VLLE) region, never measured experimentally, has been identified for mixtures of hydrogen sulfide + imidazolium ionic liquids with the [PF6] - anion at high H2S concentrations. This work illustrates that relatively simple models are able to capture the phase absorption diagram of different gases in ionic liquids, provided accurate models are available for the pure components as well as an accurate equation of state to model the behavior of complex systems. © 2012 American Chemical Society.


Al-Nehlawi A.,Research Center | Al-Nehlawi A.,Autonomous University of Barcelona | Saldo J.,Autonomous University of Barcelona | Vega L.F.,Research Center | And 3 more authors.
Meat Science | Year: 2013

The effects of an aerobic modified atmosphere packaging (MAP) (70% CO2, 15% O2 and 15% N2) with and without a CO2 3-h soluble gas stabilization (SGS) pre-treatment of chicken drumsticks were determined for various package and product quality characteristics. The CO2 dissolved into drumsticks was determined. The equilibrium between CO2 dissolved in drumsticks and CO2 in head space was reached within 48h after packaging, showing highest values of CO2 in SGS pre-treated samples. This greater availability of CO2 resulted in lower counts of TAB and Pseudomonas in SGS than in MAP drumsticks. Package collapse was significantly reduced in SGS samples. The average of CO2 dissolved in the MAP treatment was 567mg CO2kg-1 of chicken and, 361mg CO2kg-1 of chicken during the MAP treatment, in SGS pre-treated samples. This difference could be the quantity of CO2 dissolved during SGS pre-treatment.These results highlight the advantages of using SGS versus traditional MAP for chicken products preservation. © 2013 Elsevier Ltd.


Lopez-Aranguren P.,CSIC - Institute of Materials Science | Lopez-Aranguren P.,Research Center | Vega L.F.,Research Center | Vega L.F.,Air Products Group | Domingo C.,CSIC - Institute of Materials Science
Chemical Communications | Year: 2013

The present work focuses on the development of a new eco-efficient method, based on the use of compressed CO2 as a solvent, reaction medium and catalyst, for the in situ polymerization of ethyleneimine inside mesoporous silica. © 2013 The Royal Society of Chemistry.


Lopez-Aranguren P.,CSIC - Institute of Materials Science | Lopez-Aranguren P.,Research Center | Saurina J.,University of Barcelona | Vega L.F.,Research Center | And 2 more authors.
Microporous and Mesoporous Materials | Year: 2012

The internal surface of micro and nanoporous substrates can be modified in terms of charge, functionality or even reactivity or stability by means of bifunctional organic molecules able to self-assembly. This work investigates the impregnation with trialkoxysilanes of porous systems using supercritical carbon dioxide (scCO2) as a solvent, which combines several advantages such as liquid-like density and high solvating power with gas-like transport properties. Moreover, scCO2 does not have specific interactions with the substrate and there is no competition for absorption between added reagents and solvent molecules. The work aims at describing a generic liquid-solventless impregnation method applicable to macro (perlite), meso (silica gels and agglomerated nanoparticles) and microporous (zeolite) silica-based substrates using scCO2. The hydrophobic octyltriethoxysilane was used to impregnate the internal surface of the chosen substrates with the objective of obtaining high capacity oil adsorbents. FTIR, TGA and N2 adsorption isotherms were used to determine the interactions between the substrate and the silane deposited monolayer. The acquired hydrophobic character was evaluated using the Karl Fischer method to measure the loss in water adsorption capacity after silane grafting. © 2011 Elsevier Inc. All rights reserved.


Builes S.,Research Center | Lopez-Aranguren P.,Research Center | Lopez-Aranguren P.,CSIC - Institute of Materials Science | Fraile J.,CSIC - Institute of Materials Science | And 3 more authors.
Journal of Physical Chemistry C | Year: 2012

Solid sorbents are considered as a potentially less-energy-intensive alternative to the use of liquids for the removal and separation of liquid and gaseous fluids. The control of the surface characteristics of porous inorganic materials via the deposition of an organic layer is of great interest for tailoring the properties of the sorbent. For instance, organic functionalization of traditional solid sorbents (micro- and mesoporous silica and silicates) allows tuning their surface properties, such as hydrophilicity or hydrophobicity and surface reactivity. However, the underlying mechanism of the sorption process in highly complex organic functionalized materials is not yet fully understood. This incomplete understanding limits the possibilities of designing optimal adsorbents for different applications increasing the interest in performing complementary experimental-simulation studies. In this work, the adsorption of N 2 in alkylsilane-modified disordered mesoporous silica (silica gel 40) and crystalline aluminosilicate (zeolite Y) is analyzed by a combination of experiments and simulations. The goal of the adsorption simulation study was two-fold: first, to assess the ability of using grand canonical Monte Carlo to obtain quantitative predictions of the adsorption characteristics of gases on alkylsilane postfunctionalized products and, second, to provide new insights into the adsorption mechanism. A supercritical silanization experimental method was used for the postmodification of the internal surface of the studied porous substrates. This work demonstrates that even though the models of amorphous hybrid materials require simplifications related to the cell size and silane polymerization modes, it is possible to use these models to obtain an adequate insight of what happens in the macroscopic systems. These models allow us to acquire information on the mechanisms of silane functionalization and the interactions of the support and silane chains with the adsorbed gases. © 2012 American Chemical Society.


Llovell F.,CSIC - Institute of Materials Science | Llovell F.,Research Center | Vilaseca O.,CSIC - Institute of Materials Science | Vilaseca O.,Research Center | And 2 more authors.
Separation Science and Technology | Year: 2012

There is an increased interest in developing accurate tools to relate the physicochemical properties of ionic liquids (ILs) to their microscopic structure as this information is needed to speed up the design of new ionic liquids for chemical and industrial processes. Molecular models can be used for this purpose. We explore here the extended capabilities of a model previously developed in the context of soft-SAFT, by Andreu and Vega in 2007 to reproduce the thermodynamic behavior of imidazolium hexafluorophosphate-based ([C nmim][PF 6]) ionic liquids. The molecular parameters optimized in the previous work have been used here in a transferable manner; some new members of the [C nmim][PF 6] family have also been added, as new recent experimental data has been published. The interfacial tensions have been calculated using a Density Gradient Approach and the results have been compared with available experimental data. The solubility of carbon monoxide and hydrogen in those ILs has been studied in the range of temperatures and pressures of application for separation processes. Binary mixtures with other imidazolium ionic liquids with different anions have been calculated, in a predictive manner. Finally, calculations of mixtures of ionic liquids with water also show very good agreement with experimental data. This work highlights the importance of using a simple but robust thermodynamic model, including the right level of interactions, to accurately describe the properties of these highly non-ideal systems. © 2012 Copyright Taylor and Francis Group, LLC.


Builes S.,Research Center | Vega L.F.,Research Center | Vega L.F.,Air Products Group
Langmuir | Year: 2013

The underlying mechanism of the adsorption process in functionalized materials is not yet fully understood. This incomplete understanding limits the possibility of designing optimal adsorbent materials for different applications. Hence, the availability of complementary methods to advance this field is of great interest. We present here results concerning the adsorption of CO 2 in amine-functionalized silica materials by Monte Carlo simulations, providing new insights into the capture process. Two different mechanisms of functionalization are compared: impregnation (a physical mixture of the amine and the support) and grafting (a chemical bond is formed between the amine and the support). We evaluate in this work a model of MCM-41 for N2 and CO2 adsorption with varying degrees of density of the functionalized chains. The results indicate that the mobility of the impregnated chains allows the creation of a network of microcavities, which enhance the low-pressure adsorption capabilities of these materials. Molecular simulations allow us to study in detail the conformational changes in the functionalized chains during the adsorption process. Materials functionalized densely by grafting undergo a change in the preferential orientation of the chains, which allows the adsorption of additional molecules close to the surface of the support. The adsorption of gas molecules close to the pore surface is usually the most energetically favorable configuration; however, for densely grafted materials the adsorption close to the surface occurs only at pressures large enough to provide energy to displace the functionalized chains. © 2012 American Chemical Society.


Lopez-Aranguren P.,CSIC - Institute of Materials Science | Lopez-Aranguren P.,Research Center | Fraile J.,CSIC - Institute of Materials Science | Vega L.F.,Research Center | And 2 more authors.
Journal of Supercritical Fluids | Year: 2014

The present work examines the functionalization of silica supports via supercritical CO2 grafting of aminosilanes, which is an important step in the preparation of materials used as solid sorbents in CO2 capture. Four materials have been considered as solid supports: two commercially available silica gels (4.1 and 8.8 nm pore diameter), the mesoporous silica MCM-41 (3.8 nm pore diameter) and a microporous faujasite of the Y type. Mono- and di-aminotrialkoxysilane were chosen for this study. The optimal operating conditions required to have free aminosilane in solution were first evaluated by studying the phase behavior of the system scCO2/aminosilane at different pressures and temperatures. FTIR spectroscopy was used to determine the chemical structure of the grafted species. Aminosilane uptake was estimated by thermogravimetric and elemental analysis. Densities up to 3-4 molecules of monoaminosilane per nm-2 were reached by using a small amount of a cosolvent together with the supercritical CO2. The samples were characterized in regards of thermal stability, showing that aminosilane groups were covalently attached to the amorphous silica surface in the mesoporous supports, but not in the microporous zeolite. Low temperature N2 and ambient temperature CO2 isotherms were recorded to establish the adsorptive behavior of the prepared hybrid materials. The amine functionalized MCM-41 and the 8.8 nm silica gel exhibited a significant higher uptake of CO2 at low pressures compared with the bare supports. On the contrary, for the 4 nm silica gel and the zeolite the adsorption decreased after impregnation. © 2013 Elsevier B.V. All rights reserved.


Builes S.,Research Center Carburos Metalicos Air Products | Vega L.F.,Research Center Carburos Metalicos Air Products | Vega L.F.,Air Products Group
Journal of Physical Chemistry C | Year: 2012

It has been demonstrated that merging the inherent sorptive behavior of amorphous silica with organic groups increases the adsorption capabilities of the solid silica. However, the underlying mechanism of the adsorption process in the functionalized materials is not fully understood, limiting the possibility of designing optimal adsorbent materials for different applications; hence, the availability of complementary methods to advance in this field is of great interest. Here we present results concerning the adsorption of CO 2 in amine-functionalized silica materials, by Monte Carlo simulations, providing new insight into the capture mechanism. We propose a simulation methodology for the design of postsynthesis-functionalized silica materials in which realistic model adsorbents are generated using an energy bias selection scheme for the possible grafting sites. This methodology can be applied to different materials. In this work, we evaluate a model MCM-41 for CO 2 adsorption using grand canonical Monte Carlo simulations, and compared the results with available experimental data. A new methodology is presented, which allows accounting for the chemisorbed CO 2 on the adsorption isotherms. The results indicate that although chemisorption is an important part of this process at low pressures, physisorption also plays a significant role in the capture of CO 2 in these materials. Functionalization increases the interactions of the CO 2 molecules with the surface, whereas it decreases the available space for adsorption of CO 2; the overall efficiency of the improved adsorption lies on the availability of adsorption space versus stronger interactions. In addition to the adsorption isotherms, we studied the configurations of the amine chains during the adsorption process for different degrees of functionalization as well as the effect of the concentration of grafted amines on the adsorption isotherm. The overall results show that molecular simulations serve as a guide to quantify the CO 2 amount that can be easily sorbed for carbon capture applications, highlighting the importance of this approach. © 2012 American Chemical Society.

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