Browsing by Author "Valentini, Antoninho"

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    Amorphization effects on the basic sites of nanometric magnesium oxide.
    (2008) Carreño, Neftalí Lenin Villarreal; Keyson, David; Escote, Marcia Tsuyama; Leite, Edson Roberto; Longo, Elson; Fajardo, Humberto Vieira; Probst, Luiz Fernando Dias; Valentini, Antoninho; Joya, Miryam Rincón; Pizani, Paulo Sergio
    The paper reports the catalytic action of the basic sites of nanocrystalline particles of rare earth-doped magnesium oxide in the aldolization reaction between acetone and methanol leading to the C–C bond formation of an a,b-unsaturated compound (methyl vinyl ketone), also forming methyl ethyl ketone and isopropyl alcohol. Undoped and doped MgO samples were prepared by high-energy mechanical milling of commercial Mg, Y and Ce oxide powders. Catalytic activity and surface basicity of these compounds were strongly influenced by doping and the time of mechanical milling (amorphization process). Such milling leads to the formation of nanocrystalline materials. Influence of mechanical processing of these compounds was investigated by means of N2 adsorption (BET), X-ray diffraction (XRD), TEM, CO2 chemisorption and room temperature photoluminescence emission. Strong changes of polar groups such as hydroxyl groups on the surface of the solid were directly related to the photoluminescence emission observed.
  • No Thumbnail Available
    Item
    Application of Al2O3/AlNbO4 in the oxidation of aniline to azoxybenzene.
    (2019) Batalha, Daniel Carreira; Luz, Sulusmon Cesar; Taylor, Jason Guy; Fajardo, Humberto Vieira; Noremberg, Bruno S.; Cherubin, Igor José da Silva; Silva, Ricardo Marques e; Gonçalves, Margarete Regina Freitas; Bergmann, Carlos Pérez; Valentini, Antoninho; Carreño, Neftalí Lenin Villarreal
    Al2O3/AlNbO4 powder was fabricated by a facile high-energy milling process. The precursor materials, Al2O3 and Nb2O5, are readily available and have very attractive properties. Moreover, the catalytic activity of the sample in the liquid phase oxidation of aniline (OA) in the presence of hydrogen peroxide as oxidant was evaluated. The catalyst was found to be highly efficient and selective in the oxidation of aniline to azoxybenzene under mild conditions. When mixed with 28% AlNbO4 the alumina-based catalyst achieved high conversion and selectivity and very similar to the pure Nb2O5.
  • No Thumbnail Available
    Item
    Hydrogen production from ethanol steam reforming over Ni/CeO2 nanocomposite catalysts.
    (2007) Fajardo, Humberto Vieira; Probst, Luiz Fernando Dias; Carreño, Neftalí Lenin Villarreal; Garcia, Irene Teresinha Santos; Valentini, Antoninho
    The organic polymer chitosan was used as the polymeric precursor for the synthesis of Ni/CeO2 nanocomposite catalysts. The materials were characterized by N2 physisorption, H2 chemisorption, AA, XRD, TGA, TPR, SEM and TEM analyses. The catalysts provide very good reactivity in ethanol steam reforming compared to the conventional Ni/CeO2 catalyst prepared by the impregnation method using a commercial support. High hydrogen selectivity (>75%) was obtained on Ni/CeO2 catalysts by operating at a temperature range of 325–500 C and a H2O/ C2H5OH molar ratio of 3. It was verified that the catalytic behavior could be influenced depending on the experimental conditions employed.
  • No Thumbnail Available
    Item
    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.