Browsing by Author "Nunes, Michael Ramos"

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    Carbon-coated SnO2 nanobelts and nanoparticles by single catalytic step.
    (2009) Carreño, Neftalí Lenin Villarreal; Nunes, Michael Ramos; Garcia, Irene Teresinha Santos; Orlandi, Marcelo Ornaghi; Fajardo, Humberto Vieira; Longo, Elson
    Several types of carbon nanostructures (amorphous and graphitic), for the coating of SnO2 nanobelts and nanoparticles were obtained by a single catalytic process, during methane, natural gas, and methanol decomposition using the reactivity of surface-modified SnO2 nanostructure as a nanotemplate. The nanostructured catalyst templates were based on transition metal nanoparticles supported on SnO2 nanobelts previously prepared by a carbothermal reduction process. Carbon-coated SnO2 nanopowders were also successfully synthesized for the fabrication of carbon spheres. The carbon coating process and yield, along with the nature of the nanostructured carbon, are strongly influenced by the chemically modified surface of the SnO2 nanostructure template and the chemical reaction gas composition. The preliminary catalytic activity and gas-sensing properties of these novel materials based on metal nanoparticles and carbon-coated SnO2 were determined.
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    Influence of Rare Earth Doping on the structural and catalytic properties of nanostructured tin oxide.
    (2008) Fajardo, Humberto Vieira; Longo, Elson; Probst, Luiz Fernando Dias; Valentini, Antoninho; Carreño, Neftalí Lenin Villarreal; Nunes, Michael Ramos; Maciel, Adeilton Pereira; Leite, Edson Roberto
    Nanoparticles of tin oxide, doped with Ce and Y, were prepared using the polymeric precursor method. The structural variations of the tin oxide nanoparticles were characterized by means of nitrogen physisorption, carbon dioxide chemisorption, X-ray diffraction, and X-ray photoelectron spectroscopy. The synthesized samples, undoped and doped with the rare earths, were used to promote the ethanol steam reforming reaction. The SnO2-based nanoparticles were shown to be active catalysts for the ethanol steam reforming. The surface properties, such as surface area, basicity/base strength distribution, and catalytic activity/selectivity, were influenced by the rare earth doping of SnO2 and also by the annealing temperatures. Doping led to chemical and micro-structural variations at the surface of the SnO2 particles. Changes in the catalytic properties of the samples, such as selectivity toward ethylene, may be ascribed to different dopings and annealing temperatures.
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    SnO2 nanoparticles functionalized in amorphous silica and glass.
    (2009) Carreño, Neftalí Lenin Villarreal; Nunes, Michael Ramos; Ratmann, Cristiane Wienke Raubach; Granada, Rosana L.; Krolow, Matheus Zorzoli; Orlandi, Marcelo Ornaghi; Fajardo, Humberto Vieira; Probst, Luiz Fernando Dias
    Two different routes to obtain SnO2 nanoparticles, undoped and doped with rare earth metals (Eu or Pr), are described herein. The first route was based on the polymeric precursor method that led to the obtainment of SnO2 nanoparticles dispersed in amorphous silica. The second route was simply the impregnation with SnCl4 aqueous solution of SiO2–CaO glass microparticles functionalized with hydroxyl (−OH) groups. The materials were characterized by N2 physisorption, XRD, EDS and TEM analyses. We also present the results of catalytic experiments involving the nanocrystalline composites in ethanol steam reforming. The catalytic properties of the undoped composites with SnO2 supported on SiO2–CaO glass differ from their doped analogues, however, they were both selective towards ethylene formation, in contrast to the doped composite obtained by the polymeric precursor method.
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    Synthesis of titania/carbon nanocomposites by polymeric precursor method.
    (2008) Carreño, Neftalí Lenin Villarreal; Garcia, Irene Teresinha Santos; Carreño, Leidne S. S. M.; Nunes, Michael Ramos; Leite, Edson Roberto; Fajardo, Humberto Vieira; Probst, Luiz Fernando Dias
    Here we describe a single chemical route to obtain highly dispersed nanometric Ni particles embedded in titania/carbon matrixes (amorphous and crystalline). The synthesis of these nanocomposites is based on a polymeric precursor method. The metallic Ni nanoparticles (1–15 nm) were obtained in a single process. We also present the results of photocatalytic experiments involving a series of nanocrystalline composites based on TiO2/carbon with embedded Ni nanoparticles as nanocatalysts for rhodamine 6G degradation in aqueous solution and investigate the effects of the structure and properties of the nanocomposites on their photocatalytic applications. The effect of the different annealing treatments on the formation of TiO2 nanophases (anatase and/or rutile), the size of Ni particles and the role of the residual carbon phase on the final solid are also described.