Paula Sánchez

University of Castilla-La Mancha, Ciudad Real, Castille-La Mancha, Spain

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Publications (90)96.47 Total impact

  • Applied Catalysis B: Environmental. 01/2015; 164:316–323.
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    ABSTRACT: Figure optionsDownload full-size imageDownload high-quality image (173 K)Download as PowerPoint slide
    Journal of Molecular Catalysis A Chemical 12/2014; 395:108–116. · 3.19 Impact Factor
  • ChemInform 10/2014; 45(41).
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    ABSTRACT: PRS® paraffin wax was encapsulated by means of suspension-like copolymerization of methyl methacrylate (MMA) with butyl acrylate (BA). The effects of the polymeric shell dry glass transition temperature (Tg) and the reaction temperature (Tr) were then studied. Additionally, the evolution of particle diameter, molecular weight, conversion, and Tg during polymerization was also researched. The chemical properties of the shell material (acrylic polymer), together with those found in the core material (PRS® paraffin wax), for instance: polarity and interfacial tensions, largely determine whether the morphology of the microcapsules will be thermodynamically favored or not. The high polarity of MMA (γ0 = 18 mN m−1) and BA (γ0 = 24 mN m−1) should provide a thermodynamic driving force to cover the paraffin wax droplet which would result in a core/shell thermodynamically favored structure. However, most systems are defined by kinetics rather than thermodynamics such as the monomers dry Tg and Tr. It was observed that penetration of polymer radical chains was severely limited when the dry Tg was ≥10°C above the reaction temperature, resulting in irregular and undifferentiated particles. However, penetration did occur when the copolymeric shell dry Tg was ∼10°C below the reaction temperature which led to uniform and spherical particles being synthesized. POLYM. ENG. SCI., 54:208–214, 2014. © 2013 Society of Plastics Engineers
    Polymer Engineering and Science 01/2014; 54(1). · 1.24 Impact Factor
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    ABSTRACT: Nowadays, the syngas which is obtained from the reforming of coal, biomass or natural gas contain significantly amounts of CO2 that cannot be separated and consequently, it can take part into the Fischer–Tropsch (FTS) catalytic activity. Therefore, the presence of CO2 in the syngas flow should be taken into account. In the present study, the FTS CO hydrogenation process was compared to that of CO2 on a carbon nanofibers supported Co catalyst. The influence of CO2 content in the feed stream (H2/CO/CO2 ratio) on the reaction performance in terms of conversion and selectivity to the different products was described. Both the support and the prepared catalyst were characterized by nitrogen adsorption–desorption, temperature-programmed reduction (TPR) and X-ray diffraction (XRD). Results showed that CO hydrogenation was controlled by a Fischer–Tropsch regime, whereas CO2 hydrogenation was controlled by a methanation process. When feed was composed of CO and CO2 mixtures, the catalytic activity decreased with respect to that obtained with a CO2-free feed stream. Moreover, the presence of CO2 in feed stream favored the formation of lighter hydrocarbons and could block the production of further CO2 via Water-Gas-Shift (WGS) reaction.
    Catalysis Communications 01/2014; 44:57–61. · 2.92 Impact Factor
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    ABSTRACT: The influence of alkaline (Na, K) and alkaline earth (Mg, Ca) cocations on the behaviour of Ni/β-SiC catalyst for the tri-reforming of methane has been evaluated in this work. The cocations were loaded by co-impregnation with Ni, using different cocation/Ni ratios. Catalysts were characterized by AAS, TPR, N2 adsorption, CO2-TPD and XRD after calcination, as well as by XRD and TPO after reaction. It was analyzed the effect of the cocations on the β-SiC oxidation rate, which was increased when Na or K were loaded. The presence of Mg led to a high catalytic performance and stability (with a lower coke formation) since it provoked a decrease of Ni particle size and an increase of both the interaction between nickel and promoter and the catalyst basicity. Catalysts with Ni:Mg molar ratios of 2/1 and 1/1 showed the best performance in terms of activity and stability and formation of coke. These catalysts were considered good candidates for the tri-reforming of methane.
    Applied Catalysis B: Environmental. 01/2014; s 148–149:322–329.
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    ABSTRACT: Tri-reforming of methane has proved to be a highly efficient process for obtaining synthesis gas suitable for use in the Fischer–Tropsch process and methanol synthesis. In this paper the influence of the feedstock composition on methane conversion, the H2/CO molar ratio of the synthesis gas obtained by tri-reforming of methane and the heat released or supplied to the system with a Ni/β-SiC catalyst are all described. Firstly, a factorial plus central composite design of experiments was chosen in order to optimize the independent variables selected. Then, using the experimental data obtained, a quadratic model was built. It was observed that the effect of both water and oxygen volume flow on the H2/CO molar ratio was positive while that of methane and carbon dioxide volume flow was negative. Finally, in order to obtain an energetic optimum inside the target region, the influence of the independent variables studied previously on the overall reaction heat was calculated.
    International Journal of Hydrogen Energy 04/2013; 38(11):4524–4532. · 3.55 Impact Factor
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    ABSTRACT: The technical feasibility for Fischer–Tropsch synthetic fuels production over different cobalt/SiC catalysts was studied. Silicon carbide-supported catalysts were prepared by means of incipient wetness impregnation (IWI) and characterized by N2 adsorption/desorption, acid/base titrations, XRD, TEM, TPR and pulse oxidation techniques. The bench scale catalytic performance was examined at a total pressure of 20 bar, a temperature range between 220 and 250 °C, a space velocity (GHSV) of 6000 N cm3 g−1 h−1 and using syngas with H2/CO molar ratio equal to 2. For SiC-supported catalysts, the use of a certain amount of calcium as promoter resulted in a higher basicity and a slight higher cobalt dispersion. Furthermore, particle size and the degree of reduction were found to be directly influenced by the cobalt loading. A maximum extent of reduction was found at 12–15 wt.% cobalt with little dependence on the addition of promoter. Catalytic activity provided promising Fischer–Tropsch performance with C5+ selectivity values higher than 90% in all the cases and especially on promoted catalysts (higher than 95%). In addition, promoted catalysts shifted C5+ hydrocarbon product distribution to higher molecular weight demonstrating that different commercial synthetic fuels formulations (gasoline to diesel) can be provided by modifying mCo-nCa/SiC catalyst composition.
    Catalysis Today 06/2012; 187(1):173–182. · 3.31 Impact Factor
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    ABSTRACT: Spherical microcapsules with a 49 wt % of Rubitherm® RT31 were successfully synthesized by means of suspension‐like polymerization to be used for textile applications in summer conditions. Microcapsules were fixed into seven fabric substrates for different textile applications by a coating technique without deteriorating original functionalities of the textiles. Thermal performance of different coated textiles with 35 wt % of microcapsules was evaluated by differential scanning calorimetry (DSC) and infrared thermography (IR) techniques and the physical characteristics of textiles with thermo‐regulating properties were examined by environmental scanning electron microscopy (ESEM). It was observed that all treated textile substrates allow to obtain thermo‐regulating properties with acceptable latent heat storage capacities. Results also indicated that the presence of microcapsules containing Rubitherm® RT31 produces a significant thermal insulation effect during a cold to warm transition (20–45°C). Thus, this kind of microcapsules can be used to obtain textiles with thermal comfort‐related properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
    Journal of Applied Polymer Science 06/2012; 124(6). · 1.40 Impact Factor
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    ABSTRACT: In this work, the CO(2) capture capacity of different types of carbon nanofibers (platelet, fishbone, and ribbon) and amorphous carbon have been measured at 26 °C as at different pressures. The results showed that the more graphitic carbon materials adsorbed less CO(2) than more amorphous materials. Then, the aim was to improve the CO(2) adsorption capacity of the carbon materials by increasing the porosity during the chemical activation process. After chemical activation process, the amorphous carbon and platelet CNFs increased the CO(2) adsorption capacity 1.6 times, whereas fishbone and ribbon CNFs increased their CO(2) adsorption capacity 1.1 and 8.2 times, respectively. This increase of CO(2) adsorption capacity after chemical activation was due to an increase of BET surface area and pore volume in all carbon materials. Finally, the CO(2) adsorption isotherms showed that activated amorphous carbon exhibited the best CO(2) capture capacity with 72.0 wt % of CO(2) at 26 °C and 8 bar.
    Environmental Science & Technology 06/2012; 46(13):7407-14. · 5.26 Impact Factor
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    ABSTRACT: The present work was an in-depth study related to synthesis of carbon nanospheres (CNSs) at different scales (lab and pilot) with the end goal to economize the production of these materials on a large scale. Synthesis of large amounts of CNSs relies on the careful control of the operating conditions such as space velocity (helium flow rate), hydrocarbon (benzene) content in feed stream, and synthesis time. The alteration of these variables caused important changes in both the yield and properties of the obtained materials. In general, characterization results of the synthesized CNSs demonstrated that they showed low BET surface area and pore volume values typical of spherical geometrical bodies, good thermal stability, and good crystallinity. Normally, CNSs are presented as conglomerates as consequence of the accretion via the carbon atoms at the edge of the “curling” graphitic flakes. Finally, results demonstrated a successful scale up, obtaining a CNSs yield at pilot scale considerably superior (factor of 3.9) to that obtained at laboratory scale.
    Industrial & Engineering Chemistry Research. 05/2012; 51(19):6745–6752.
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    ABSTRACT: The pyrolysis characteristics of three lignocellulosic biomasses (fir wood, eucalyptus and pine bark) and a marine biomass (Nannochloropsis gaditana microalgae) were investigated by thermogravimetric analysis coupled with mass spectrometry (TGA-MS). Thermal degradation of lignocellulosic biomass was divided into four zones, corresponding to the decomposition of their main components (cellulose, hemicellulose and lignin) and a first step associated to water removal. Differences in volatile matter and cellulose content of lignocellulosic species resulted in different degradation rates. Microalgae pyrolysis occurred in three stages due to the main components of them (proteins), which are greatly different from lignocellulosic biomass. Heating rate effect was also studied. The main gaseous products formed were CO(2), light hydrocarbons and H(2)O. H(2) was detected at high temperatures, being associated to secondary reactions (char self-gasification). Pyrolysis kinetics were studied using a multiple-step model. The proposed model successfully predicted the pyrolytic behaviour of these samples resulting to be statistically meaningful.
    Bioresource Technology 04/2012; 109:163-72. · 5.04 Impact Factor
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    ABSTRACT: The hydrogen adsorption capacity of different types of carbon nanofibers (Platelet, Fishbone and Ribbon) and amorphous carbon has been measured as a function of pressure and temperature. Results have showed as the more graphitic/ordered carbon materials adsorbed less hydrogen than the more amorphous ones. After that and, with the aim of improve the hydrogen adsorption capacity of these carbon materials, they were functionalizated (oxygen surface groups incorporation) and Ni-modificated. Results also showed an important increase of the H2 adsorption capacity despite the porosity loss that took place after the treatments. Due to the advantages of functionalization and Ni-modification, both treatments were applied at the same time over the most promising carbon materials from the H2 adsorption point of view, observing again an improvement of the hydrogen adsorption capacity. Finally, the H2 adsorption capacity of chemically activated carbon materials increased considerably due the pore structure development and even more if activated materials were Ni-modificated.
    International Journal of Hydrogen Energy 03/2012; 37(5):4144–4160. · 3.55 Impact Factor
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    ABSTRACT: The hydrogen adsorption capacity of different types of carbon nanofibers (platelet, fishbone and ribbon) and amorphous carbon have been measured as a function of pressure and temperature. The results showed that the more graphitic carbon materials adsorbed less hydrogen than more amorphous materials. After a chemical activation process, the hydrogen storage capacities of the carbon materials increased markedly in comparison with the non-activated ones.BET surface area of amorphous carbon increased by a factor of 3.5 and the ultramicropore volume doubled, thus increasing the hydrogen adsorption by a factor of 2. However, BET surface area in platelet CNFs increased by a factor of 3 and the ultramicropore volume by a factor of 6, thus increasing the hydrogen storage by a factor of 4.5. The dependency of hydrogen storage capacity of carbon materials on the BET surface area was evaluated using both a condensation model and experimental results. Comparison of data suggests that the hydrogen adsorption capacity clearly depends on the pore structure and so, on the accessibility to the internal surface.
    Applied Surface Science 01/2012; 258(7):2498–2509. · 2.54 Impact Factor
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    ABSTRACT: The effects of the addition of alkali metal and alkali-earth metal promoters over cobalt based catalyst on Fischer–Tropsch activity and on hydrocarbon product distribution were studied. The influence of promoters on the reducibility and cobalt particle size was studied by different techniques, including N2 adsorption, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption and acid–base titrations. Experiments were carried out on a bench scale fixed bed reactor and catalysts were prepared by incipient wetness impregnation. It was observed that the addition of small amounts of these promoters (0.5wt%) improved the cobalt oxide reducibility by reducing the formation of cobalt aluminate species. The interaction between cobalt oxide and promoted support was reduced and larger cobalt oxide particles were formed on the surface. A positive correlation between basicity and particle size was observed with the exception of K promoted sample. Furthermore, CO conversion and C5+ selectivity were found to be also influenced by the addition of promoters. An enhanced dispersion that provides abundant catalytically active sites was observed on promoted catalyst. The addition of Ca to the cobalt based catalyst greatly improved the diesel selectivity. However Ca promoted catalyst yield a higher amount of methane at 242°C than the Na sample.
    Catalysis Today 06/2011; 167(1):96-106. · 3.31 Impact Factor
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    ABSTRACT: Ruthenium supported on carbon nanofibers with different structures with respect to the arrangement of the graphitic planes (platelet, fishbone and tubular) have been prepared by wet impregnation method. On the other hand, the CNFs were prepared by CVD method at different temperatures using C2H4 as the carbon precursor and Ni/SiO2 as the catalyst. Different techniques have been employed to characterize both the supports and the final Ru catalysts: N2 adsorption–desorption analyses, XRD, TEM, elemental analyses, TPD, TPR, H2 chemisorption, TPO, atomic absorption spectrophotometry and titration analyses. The results show that, depending on the orientation of the graphitic plane, the amount of acidic oxygen-containing groups can change significantly when the Ru was added to the CNFs. Thus, the specific surface area of CNF tubular was increased when Ru particles were impregnated. It was due to the oxygen groups were increased in comparison with other CNF types. In turn, the Ru particle size, its dispersion and its interaction with the support were clearly influenced by these oxygen-containing groups. Therefore, it was demonstrated that the presence of more acidic groups stabilizes the Ru particles during reduction.
    Chemical Engineering Journal. 01/2011; 168(2):947-954.
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    ABSTRACT: The liquid-phase oxidation of glycerol has been studied on gold nanoparticles supported on different carbon materials: activated carbon (AC), graphite (G) and carbon ribbon-type nanofibers (CNF-R). Catalysts were prepared by two different methods: impregnation (-IMP) and gold-sol (-SGT). The influence of the operating conditions (e.g. pressure, temperature, NaOH/glycerol molar ratio and glycerol/Au molar ratio) on the catalytic activity and product selectivity was studied in detail. The oxygen pressure was found to have a very small influence on the reaction rates, with the reaction being zero order with respect to oxygen. The selectivity to glyceric acid was significantly enhanced on increasing both the oxygen pressure and reaction temperature, which simultaneously led to a decrease in both glycolic and tartronic acid selectivities. Glycerol conversion and glyceric acid selectivity increased on increasing the NaOH/glycerol molar ratio in the range from 1 to 2. At higher values of this molar ratio, these two parameters remained approximately constant. A linear correlation was observed between glycerol conversion and the amount of catalyst (up to 0.5 g) and this indicates that the reaction was kinetically controlled. However, along with the increase in the catalytic activity with the amount of catalyst, a substantial decrease in the selectivity to glyceric acid was also observed. Finally, a kinetic model to describe the reaction mechanism was proposed and good agreement between the experimental and predicted values was achieved.Highlights► The product distribution for the oxidation of glycerol is clearly dependent on the reaction conditions. ► The oxygen pressure was found to have a very small influence on the reaction rates. ► The selectivity to glyceric acid was significantly enhanced by an increase of reaction temperature. ► Glycerol conversion and glyceric acid selectivity increased when the NaOH/glycerol molar ratio. ► For amounts of catalyst up to 0.5 g, the reaction was reaction-rate controlled.
    Chemical Engineering Journal. 01/2011; 178:423-435.
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    ABSTRACT: A mechanistic kinetic model has been study to describe the bench scale water-gas shift reaction over a commercial presulfided CoMo catalyst using an industrial coal-derived gas feed. A rigorous kinetic network has been considered on the basis of formate, associative and direct oxidation mechanisms. Kinetic models were derived by using LHHW formalism and steady-state approximation for reaction intermediates. Kinetic parameters were estimated by nonlinear regression of the experimental data using the Marquardt–Levenberg algorithm. The WGS kinetic data were measured by experiments over a wide range of reaction conditions and comparisons for various rate equations were also established. A preliminary discrimination resulted in the necessity of rewrite models as a unique parameter models. The model based on direct oxidation mechanism successfully predicted the CO2 formation within the range of experimental conditions (high pressure and temperature). WGS rate expressions based on the regenerative process (oxidation-reduction) with the assumption that CO2 desorption reaction can be regarded as the rate determining step were found to be the best.
    Fuel and Energy Abstracts 01/2011; 36(16):9673-9684.
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    ABSTRACT: Ni and Ru impregnated carbon nanofibers (CNFs) have been for the first time successfully applied to an Y2O3-stabilized ZrO2 (YSZ) solid electrolyte to form a catalyst-electrode cell. The catalytic and electrocatalytic properties of this composite Ni or Ru CNFs have been investigated in the CO2 hydrogenation reaction under atmospheric pressure and at temperatures 200–440°C. The only products observed are methane and CO under open circuit and electrochemical promotion conditions. Ni based catalyst-electrodes show methane selectivity up to 55% at 300°C, while the Ru based catalyst exhibits selectivity up to 75% at 390°C. Negative applied potential enhances mildly the hydrogenation rate and the selectivity to CH4 in the case of Ni catalyst-electrodes. Ru based catalyst exhibit under negative applied potential an enhanced hydrogenation rate with no further remarkable improvement of methane selectivity.
    Applied Catalysis B-environmental - APPL CATAL B-ENVIRON. 01/2011; 107(1):210-220.
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    ABSTRACT: Polystyrene microcapsules containing Rubitherm® RT31 were prepared by suspension-like polymerization method using different suspension stabilizers. These microcapsules could be applied to the textiles in a variety of processes to improve thermal comfort of end-use products. The effects of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), arabic gum and gelatin as suspension stabilizers were investigated regarding thermal properties, particle size distributions, morphologies using differential scanning calorimetry, scanning electron microscopy and laser light scattering analyses.The type of suspension stabilizer had a significant effect on the particle size distribution and the morphology of the synthesized microcapsules. Spherical and regular microcapsules with smooth surface were obtained using PVP and gelatin as suspension stabilizers. However, with arabic gum and PVA irregular particles with rough surface were produced due to the interfacial tension between the polymer and the aqueous phase was close to that between PCM and polymer contacted the aqueous phase. On the other hand, the lowest average particle size in number and in volume was obtained for polyvinylpyrrolidone. The highest amount of Rubitherm® RT31 encapsulated was 67.9wt.% for arabic gum.
    Colloids and Surfaces A-physicochemical and Engineering Aspects - COLLOID SURFACE A. 01/2011; 390(1):62-66.