Browsing by Author "Leite, Edson Roberto"
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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 Discovering a selective semimetal element to increase hematite photoanode charge separation efficiency.(2019) Nogueira, André Esteves; Soares, Mario Rodrigo Santos; Souza Junior, João Batista; Ospina Ramirez, Carlos Alberto; Souza, Flavio Leandro de; Leite, Edson RobertoThis work describes a colloidal deposition process that exploits the thermal spreading ability of Sb over a hematite surface to obtain a mesoporous film with extensive open porosity and high degree of Sb5+ dispersion. The addition of Sb increased the efficiency of water oxidation by a factor of 4.5 and photocurrent at 1.23 VRHE by a factor of 6.5 compared to those of an unmodified hematite film prepared under the same conditions. The overall efficiency increase for water oxidation is attributed to more efficient charge separation. Sb was found to be an excellent selective semimetal modifier with high dispersion over the material.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 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 Preparation, characterization and catalytic properties of titanium oxide nanoparticles coated with aluminum oxide.(2011) Carreño, Neftalí Lenin Villarreal; Leite, Edson Roberto; Libanori, Rafael; Probst, Luiz Fernando Dias; Fajardo, Humberto VieiraIn the present study, TiO2 nanopowder was partially coated with Al2O3 precursors generated by a polymeric precursor method in aqueous solution. The system of nanocoated particles formed an ultra thin structure on the TiO2 nanoparticle surfaces, where the particle is the core and the nanocoating (additive) is the shell. The nanocoating 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. Ethylene production was disfavored and selectivity toward acetaldehyde, hydrogen and ethane increased with increasing Al2O3 content in the catalysts. It is important to highlight that the TiO2–Al2O3 catalysts presented satisfactory values of selectivity toward hydrogen, in spite of the deactivation observed during the period of the test.Item 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 DiasHere 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.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.