Paula Sánchez

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

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Publications (90)240.46 Total impact

  • Applied Catalysis B Environmental 03/2015; 164:316–323. · 6.01 Impact Factor
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    Journal of Molecular Catalysis A Chemical 12/2014; 395:108–116. · 3.68 Impact Factor
  • ChemInform 10/2014; 45(41).
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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 04/2014; s 148–149:322–329. · 6.01 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. · 3.32 Impact Factor
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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: A pilot plant was designed to evaluate the degradation of (heat transfer fluids) HTF for their application in (concentrating solar power) plants CSP. Firstly, the characterization of six HTFs was carried out: two ionic liquids ([BMIM][BF4] and [EMIM][BF4]), two molten salts (Hitec XL and solar salt), a commercial HTF (Mobiltherm 605) and an oil extracted from Nannochloropsis gaditana microalgae (NG oil). Mobiltherm 605 was selected for tuning the pilot plant due to its similarity to HTFs used in CSP, low cost and easy acquisition. The operating conditions were set according to thermogravimetric analysis. Thus, three isothermal experiments were carried out at 140, 160 ant 180 °C for 15 days. Mobiltherm 605 viscosity increased with time indicating that polymerization of hydrocarbon chains took place. Two mathematical models were developed to assess the HTF behaviour in the pilot plant. A mathematical model for the estimation of the most representative parameters (viscosity, heat capacity and overall heat transfer coefficient) of HTF performance was proposed. Furthermore, an activation/deactivation model was proposed to predict the variation of the estimated parameters with time. This model was validated with experimental viscosity measurements (average error of about 3%). Finally, the statistical significance of the model was proved.
    Energy 06/2013; 54:240–250. · 4.16 Impact Factor
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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. · 2.93 Impact Factor
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    ABSTRACT: The aim of the work described here is to evaluate the catalytic performance in the tri-reforming process of Ni/CeO2 and Ni/β-SiC catalysts prepared by using four different nickel salts (nitrate, acetate, chloride and citrate). Metal particles supported over ceria had bigger particle sizes (leading to lower metal-support interactions) than those supported on β-SiC. It was also demonstrated that the metal salt used in the preparation of Ni-based catalysts had a marked influence on the size of the nickel particles. Larger particles with a worse catalytic behaviour were obtained when nickel chloride and nickel citrate were used as the precursors of Ni supported species. Methane consumption rate and H2/CO ratio in the effluents were influenced by the type of support and salt precursor used in the preparation of the catalysts. CO2-TPD proved that catalysts based on ceria as the support presented more basic sites, which was related to a decrease of the H2/CO molar ratio in the effluents coming from the reactor. High methane consumption rate and good catalytic stability were obtained when nickel nitrate and nickel acetate were used to prepare Ni/β-SiC catalysts. The results showed that these latter catalysts can be considered as promising ones for the tri-reforming process.
    Applied Catalysis A General 07/2012; s 431–432:49–56. · 3.67 Impact Factor
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    ABSTRACT: High pressure Water Gas Shift performance over a commercial non-sulfide CoMo catalyst was studied in a bench scale set-up, using an industrial coal-derived syngas feed. CO conversion showed an important dependence on both reaction temperature and space velocity but remained almost constant with increasing H2Ov/CO molar ratios. Hydrogen selectivity showed the same trend although it was enhanced with increasing H2Ov/CO molar ratios. The effect of the activation method on CO conversion was also studied. Despite non-sulfide CoMo catalysts have been widely considered as non-active for WGS reaction, a surprisingly high CO conversion comparable to that attained by the sulfide one, was displayed by this catalyst in the range of conditions studied. However, non-sulfide CoMo catalyst still resulted in lower conversion values if compared with pre-sulfide one.
    Fuel 07/2012; 97:428–434. · 3.41 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). · 1.64 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. · 5.48 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. · 2.24 Impact Factor
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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. · 2.93 Impact Factor
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    ABSTRACT: The thermal properties of microcapsules containing carbon nanofibers (CNFs) suspended in ethyl phenylacetate (EPA) were investigated by thermogravimetric analysis coupled with mass spectrometry (TGA–MS). The pyrolysis of these microcapsules consisted of two stages. During the first one (100–150 °C), the emissions of aromatic compounds coming from the decomposition of EPA were identified. In the second one (150–290 °C), NH2–CO coming from primary amide decomposition was mainly detected.A multiple-step model was used to predict the thermal decomposition of the synthesized microcapsules under both inert and oxidant atmospheres. Furthermore, pyrolysis and combustion kinetic parameters such as pre-exponential factor and activation energy of these microcapsules were estimated by nonlinear regression. An excellent agreement between experimental and predicted data was observed and confirmed from the statistical point of view.
    Journal of Analytical and Applied Pyrolysis 03/2012; 94:246–252. · 3.07 Impact Factor
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    ABSTRACT: Microencapsulation of carbon nanofibers (CNFs) suspended in an organic phase with a polymer shell of poly(urea–formaldehyde) by in situ polymerization has been carried out. The encapsulation efficiency of CNFs and ethyl phenylacetate (EPA), the morphology and the particle size distribution of the obtained microcapsules were determined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), optical microscopy (OM), environmental scanning microscopy (ESEM), laser diffraction and mercury porosimeter. TGA and DSC data were in agreement with the OM and ESEM analysis demonstrating that the synthesized microcapsules consisted of poly(urea formaldehyde) (shell material), EPA and small amount of CNFs (core materials). Furthermore, the presence of nanopores in the shells of obtained microcapsules provides a versatile platform for the further development of numerous promising applications. The influence of the CNFs weight fraction in the core material on the encapsulation efficiency, the morphology and the particle size distribution were also studied. The amount of CNFs does not have a significant effect on the encapsulation of EPA. Microcapsules containing CNFs and EPA as core material had a particle size bigger than microcapsules only containing EPA. These microcapsules containing CNFs could be considered to have potential as structural materials, electrochemical sensors, field emission displays and nanometer sized semiconductor devices.
    Chemical Engineering Journal 02/2012; s 181–182:813–822. · 4.06 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 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 12/2011; 178:423-435. · 4.06 Impact Factor