Recursos de colección

RUA (124.683 recursos)

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INV - LMA - Artículos de Revistas

Mostrando recursos 1 - 8 de 8

  1. Mesophase pitch-derived graphite foams with selective distribution of TiC nanoparticles for catalytic applications

    Molina Jordá, José Miguel
    TiC-supported metals are systems of great importance in catalysis science and technology. Albeit their interest, catalysts based on monoliths consisting of TiC-containing carbonaceous foams have not yet been fabricated. This work aims to present a route for fabrication of mesophase pitch-derived open-pore graphite foams with TiC nanoparticles selectively distributed in two locations: at the surface of the pore cells, able for metal-support, and in the bulk, essential to achieve high degree of graphitization for enhancement of thermal conductivity. The double distinctive effect of the nanoparticles in the monoliths makes these materials interesting to be checked in catalytic applications.

  2. Effects of infiltration pressure on mechanical properties of Al–12Si/graphite composites for piston engines

    Narciso, Javier; Molina Jordá, José Miguel; Rodríguez Guerrero, Alejandro; Rodríguez Reinoso, Francisco; Louis, Enrique
    In this work results for the flexural strength and the thermal properties of interpenetrated graphite preforms infiltrated with Al-12wt%Si are discussed and compared to those for packed graphite particles. To make this comparison relevant, graphite particles of four sizes in the range 15–124 μm, were obtained by grinding the graphite preform. Effects of the pressure applied to infiltrate the liquid alloy on composite properties were investigated. In spite of the largely different reinforcement volume fractions (90% in volume in the preform and around 50% in particle compacts) most properties are similar. Only the Coefficient of Thermal Expansion is 50% smaller...

  3. Carbon nanotube-supported Ni–CeO2 catalysts. Effect of the support on the catalytic performance in the low-temperature WGS reaction

    Dongil, Ana Belén; Pastor Pérez, Laura; Escalona, Néstor; Sepúlveda-Escribano, Antonio
    The low temperature water-gas shift (WGS) reaction has been studied over two commercial multiwall carbon nanotubes-supported nickel catalysts promoted by ceria. For comparison purposes, activated carbon-supported catalysts have also been studied. The catalytic performance and the characterization by N2 adsorption analysis, powder X-ray diffraction (XRD), temperature-programmed reduction with H2 (TPR-H2), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis showed that the surface chemistry has an important effect on the dispersion of ceria. As a result, ceria was successfully dispersed over the carbon nanotubes (CNTs) with less graphitic character, and the catalyst afforded better activity in WGS than the...

  4. Synthesis of palladium nanoparticles on carbon nanotubes and graphene for the chemoselective hydrogenation of para-chloronitrobenzene

    Dongil, Ana Belén; Pastor Pérez, Laura; Fierro, J.L.G.; Escalona, Néstor; Sepúlveda-Escribano, Antonio
    We have studied the synthesis of palladium nanoparticles over carbon nanotubes (Pd/CNT) and graphene (Pd/G) and we have tested their catalytic performance in the liquid phase chemoselective hydrogenation of para-chloronitrobenzene at room temperature. The catalysts were characterized by N2 adsorption/desorption isotherms, TEM, X-ray diffraction, infrared and X-ray photoelectron spectroscopy and ICP-OES. The palladium particle size on Pd/G (3.4 nm) and Pd/CNT (2.8 nm) was similar though the deposition was higher on Pd/G. Pd/CNT was more active which can be ascribed to the different surface area and electronic properties of the Pd nanoparticles over CNT, while the selectivity was 100% to...

  5. Synthesis of palladium nanoparticles over graphite oxide and carbon nanotubes by reduction in ethylene glycol and their catalytic performance on the chemoselective hydrogenation of para-chloronitrobenzene

    Dongil, Ana Belén; Pastor Pérez, Laura; Fierro, J.L.G.; Escalona, Néstor; Sepúlveda-Escribano, Antonio
    Pd nanoparticles have been synthesized over carbon nanotubes (CNT) and graphite oxide (GO) by reduction with ethylene glycol and by conventional impregnation method. The catalysts were tested on the chemoselective hydrogenation of p-chloronitrobenzene and the effect of the synthesis method and surface chemistry on their catalytic performance was evaluated. The catalysts were characterized by N2 adsorption/desorption isotherms at 77 K, TEM, powder X-ray diffraction, thermogravimetry, infrared and X-ray photoelectron spectroscopy and ICP-OES. It was observed that the synthesis of Pd nanoparticles employing ethylene glycol resulted in metallic palladium particles of smaller size compared to those prepared by the impregnation method...

  6. Environmentally friendly reduction of a platinum catalyst precursor supported on polypyrrole

    Buitrago Sierra, Robison; García Fernández, María Jesús; Pastor-Blas, M. Mercedes; Sepúlveda-Escribano, Antonio
    Supported metals are traditionally prepared by impregnating a support material with the metal precursor solution, followed by reduction in hydrogen at elevated temperatures. In this study, a polymeric support has been considered. Polypyrrole (PPy) has been chemically synthesized using FeCl3 as a doping agent, and it has been impregnated with a H2PtCl6 solution to prepare a catalyst precursor. The restricted thermal stability of polypyrrole does not allow using the traditional reduction in hydrogen at elevated temperature, and chemical reduction under mild conditions using sodium borohydride implies environmental concerns. Therefore, cold RF plasma has been considered an environmentally friendly alternative. Ar...

  7. Desilication of TS-1 zeolite for the oxidation of bulky molecules

    Silvestre Albero, Ana; Grau-Atienza, Aida; Serrano, Elena; Garcia-Martinez, Javier; Silvestre-Albero, Joaquín
    A series of modified TS-1 samples have been produced by desilication of the original TS-1 (4 wt.% Ti) using a chemical treatment with NaOH. Desilicated TS-1 zeolites exhibit a large BET surface area together with a well-developed mesoporosity. The hierarchical catalysts from desilication of TS-1 zeolite show a good catalytic activity for the oxidation of small molecules and a significantly higher activity for the oxidation of bulky molecules.

  8. Spin alignment of extra electrons in K-phenanthrene clusters taken from the crystalline tripotassium-intercalated phenanthrene structure

    Vergés Brotons, José Antonio; Andres, Pedro L. de; San-Fabián, Emilio; Chiappe, Guillermo; Louis, Enrique; Guijarro, Albert
    The appearance of ferromagnetic correlations among π electrons of phenanthrene (C14H10) molecules in the herringbone structure is proven for K doped clusters both by ab initio quantum-chemistry calculations and by the direct solution of the many-body Pariser-Parr-Pople Hamiltonian. Magnetic ground states are predicted for one or three additional electrons per phenanthrene molecule. These results are a consequence of the small overlap between the lowest unoccupied molecular orbitals (and lowest unoccupied molecular orbitals + 1) of neutral neighboring phenanthrene molecules, which makes the gain in energy by delocalization similar to the corresponding increase due to the Coulomb interaction.

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