Browsing by Author "Longo, Elson"
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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 SergioThe 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.Item 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, ElsonSeveral 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.Item Correlation of catalytic oxidation and ionic conductivity properties of nanostructured gadolinium-doped ceria.(2021) Godinho Júnior, Mário; Rodrigues, Murillo H. M.; Gonçalves, Rosana de Fátima; Roca, Román Alvarez; Longo, Elson; Mota, Fabiana Villela; Fajardo, Humberto Vieira; Balzer, RosanaThis paper reports the relationship between ionic conductivity and catalytic activity of ionic conductors based on gadolinium-doped ceria (GDC) at different temperatures. The samples have been characterized by transmission electron microscopy techniques, and the results indicated a highly homogeneous particle size, which confirmed their nanometric size. Afterward, the structure determined using X-ray diffraction analysis has been used to analyze the effect of dopant insertion. Lastly, ionic conductivity data were obtained using the impedance technique and were compared with the conversion rates of volatile organic compounds using GDC heterogeneous catalysts. The samples containing 15% gadolinium presented higher catalytic activity for the oxidation of n hexane (82,5%) as well as higher ionic conductivity at 400 ◦C (3.09 × 10− 4 S⋅cm− 1 ). An attempt is made to correlate conductivity and catalytic oxidation in terms of oxygen mobility, vacancies, and superoxide formation.Item Gadolinium-doped cerium oxide nanorods : novel active catalysts for ethanol reforming.(2010) Godinho, Mario; Gonçalves, Rosana de Fátima; Leite, Edson Roberto; Ratmann, Cristiane Wienke Raubach; Carreño, Neftalí Lenin Villarreal; Probst, Luiz Fernando Dias; Longo, Elson; Fajardo, Humberto VieiraThe gadolinium-doped ceria nanorods (Gd0.2 Ce0.8O2-x) were synthesized by hydrothermal treatment. It was shown that the use of microwave heating during hydrothermal treatment decreases the treatment time required to obtain gadolinium-doped ceria nanorods and that oriented attachment is the dominant mechanism responsible for anisotropic growth. It was clear that Gd0.2 Ce0.8O2-x nanorods were more catalytically active than commercial CeO2 in the ethanol reforming reaction.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 RobertoNanoparticles 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.Item Influence of support on catalytic behavior of nickel catalysts in the steam reforming of ethanol for hydrogen production.(2010) Fajardo, Humberto Vieira; Longo, Elson; Mezalira, Daniela Zambelli; Nuernberg, Giselle De Boit; Almerindo, Gizelle Inácio; Collasiol, André; Probst, Luiz Fernando Dias; Garcia, Irene Teresinha Santos; Carreño, Neftalí Lenin VillarrealAl2O3, MgO, SiO2 and ZnO-supported nickel catalysts were prepared and evaluated in the ethanol steam reforming for hydrogen production. It is shown that the catalytic behavior can be influenced depending on the experimental conditions employed and chemical composition of the catalyst.Item Microwave hydrothermal synthesis, characterisation, and catalytic performance of Zn1−xMnxO in cellulose conversion.(2014) Bernardi, Maria Inês Basso; Araújo, Vinicius D.; Ribeiro, Caue; Avansi Junior, Waldir; Longo, Elson; Albuquerque, Nilson J. A. de; Meneghetti, Simoni Margareti Plentz; Almeida, Rusiene Monteiro de; Fajardo, Humberto VieiraWurtzite-type Zn1−xMnxO (x = 0, 0.03, 0.05, 0.07) nanostructures were successfully synthesised using a simple microwave-assisted hydrothermal route and their catalytic properties were investigated in the cellulose conversion. The morphology of the nanocatalysts is dopant-dependent. Pure ZnO presented multi-plate morphology with a flower-like shape of nanometric sizes, while the Zn0.97Mn0.03O sample is formed by nanoplates with the presence of spherical nanoparticles; the Zn0.95Mn0.05O and Zn0.93Mn0.07O samples are mainly formed by nanorods with the presence of a small quantity of spherical nanoparticles. The catalyst without Mn did not show any catalytic activity in the cellulose conversion. The Mn doping promoted an increase in the density of weak acid sites which, according to the catalytic results, favoured promotion of the reactionItem Nanocompósitos cerâmicos a partir do processo de moagem mecânica de alta energia.(2008) Carreño, Neftalí Lenin Villarreal; Garcia, Irene Teresinha Santos; Santos, Luís P. S.; Fabbro, Maria Tereza; Keyson, David; Leite, Edson Roberto; Longo, Elson; Fajardo, Humberto Vieira; Fajardo, Luiz Fernando DiasPb/Ti, Sn and Mg-based nanocomposite materials were prepared by the high-energy mechanical milling of commercial powders. The surface of these ceramic compounds was strongly influenced by the doping, diameter of the milling spheres and time of the mechanical milling (amorphization process). Such milling leads to the formation of nanocrystalline materials. The mechanical processing parameters of these compounds were investigated through Brunauer, Emmett and Teller isotherms, wide angle X-ray diffraction, transmission electron microscopy and CO2 adsorption.Item Synthesis, characterization and catalytic properties of nanocrystaline Y2O3-coated TiO2 in the ethanol dehydration reaction.(2012) Fajardo, Humberto Vieira; Longo, Elson; Leite, Edson Roberto; Libanori, RafaelIn the present study, TiO2 nanopowder was partially coated with Y2O3 precursors generated by a sol-gel modified route. The system of nanocoated particles formed an ultra thin structure on the TiO2 surfaces. The modified nanoparticles were characterized by high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) analysis, Zeta potential and surface area through N2 fisisorption measurements. Bioethanol dehydration was used as a probe reaction to investigate the modifications on the nanoparticles surface. The process led to the obtainment of nanoparticles with important surface characteristics and catalytic behavior in the bioethanol dehydration reaction, with improved activity and particular selectivity in comparison to their non-coated analogs. The ethylene production was disfavored and selectivity toward acetaldehyde, hydrogen and ethane increased over modified nanoparticles.