VILMARIA APARECIDA RIBEIRO

VILMARIA APARECIDA RIBEIRO

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Palladium nanoparticles supported on phosphorus-doped carbon for ethanol electro-oxidation in alkaline media
2018 - SILVA, JULIO C.M.; FREITAS, ISABEL C. de; NETO, ALMIR O.; SPINACE, ESTEVAM V.; RIBEIRO, VILMARIA A.
Palladium nanoparticles supported on carbonVulcan XC72 (Pd/C) and on phosphorus-doped carbon (Pd/P-C) were prepared by an alcohol reduction process. X-ray diffractograms of Pd/C and Pd/P-C showed the typical face-centered cubic (fcc) structure of Pd. The crystallite sizes of Pd fcc phase were around 8 nm for both samples. X-ray photoelectron spectroscopy revealed to Pd/C and Pd/P-C that Pd was found predominantly in the metallic state and to Pd/P-C, the presence of P increases the amount of oxygen on the electrocatalyst surface. The activity and stability of the electrocatalyts for ethanol electro-oxidation in alkalinemedium was investigated by cyclic voltammetry and chronoamperometry experiments. The peak current density on Pd/P-C was 50% higher than on Pd/C, while the current density measured after 30 min at − 0.35 V vs. Hg/ HgO was 65% higher on Pd/P-C than on Pd/C. The enhancement of the catalytic activity of Pd/P-C electrocatalyst might be related to the presence of higher amounts of oxygen species on the surface, which could contribute to the oxidation of intermediates formed during ethanol electro-oxidation process.
Platinum nanoparticles supported on nitrogen-doped carbon for ammonia electro-oxidation
2017 - RIBEIRO, VILMARIA A.; FREITAS, ISABEL C. de; O. NETO, ALMIR; SPINACE, ESTEVAM V.; SILVA, JULIO C.M.
Pt nanoparticles supported on carbon (Pt/C) and nitrogen-doped carbon (Pt/NC) were prepared by an alcohol-reduction process and used for ammonia electro-oxidation in alkaline media. Nitrogen-doped carbons were prepared by thermal treatment of urea and Carbon Vulcan XC72 at 800 C under argon atmosphere. The obtained materials showed the presence of face centered cubic structure of Pt and mean particle sizes in the range of 3e3.7 nm. X-ray photoelectron spectroscopy results revealed that Pt/NC 5 (carbon prepared with 5% of urea) presents more Pt on the surface than Pt/C, and the nanoparticles are predominantly in the metallic state. The electrocatalytic activity was investigated by cyclic voltammetry and chronoamperometry experiments. Pt/NC materials showed a higher electrocatalytic activity for ammonia electro-oxidation than Pt/C, whereby the material Pt/NC 5 showed the peak current density 161% higher than Pt/C. The increase of activity might be related to the high electrochemically accessible area of Pt/NC and the improvement on the interaction with water due to the nitrogen onto the support which could contribute to the oxidation of intermediate products from ammonia electro-oxidation.
Preparation of PtRu/C Electrocatalysts by borohydride reduction for methanol oxidation in acidic and alkaline medium
2017 - SANTOS, MONIQUE C.L. dos; DUTRA, RITA M.; RIBEIRO, VILMARIA A.; SPINACE, ESTEVAM V.; OLIVEIRA NETO, ALMIR
PtRu/C electrocatalysts were performed according to the borohydride reduction method and characterized by X–ray diffraction (XRD), energy dispersive analysis (EDX), transmission electron microscopy, cyclic voltammetry (CV) and polarization curves in alkaline and acidic medium. The X-ray diffraction (XRD) of PtRu/C showed Pt peaks attributed to the face-centered cubic (fcc) structure and a shift in Pt(fcc) peaks indicated that Ru was incorporated into Pt lattice. TEM results showed mean particles sizes in the range of 2.0-4.0nm for all electrocatalysts prepared: therefore, the borohydride reduction process was considered effective for the preparation of PtRu/C electrocatalysts with a different atomic ratio. The activity for the methanol oxidation in acidic and alkaline media was investigated at room temperature, by cyclic voltammetry and chronoamperometry. Cyclic voltammetry and chronoamperometry studies showed that PtRu/C (50:50) had superior performance for methanol oxidation, compared with other electrocatalysts prepared considering acidic and alkaline studies. The currents values observed for alkaline media were higher than those observed for acidic media. Polarization curves, also, showed PtRu/C (50:50) with superior performance for methanol oxidation, when compared with Pt/C, and this improvement of performance could be associated with the occurrence of the bifunctional mechanism and electronic effect.
Estudo da preparação de eletrocatalisadores Pt-Sn/C por meio da deposição superficial de Pt sobre Sn/C utilizando diferentes metodologias para aplicação na oxidação eletroquímica do etanol
2015 - RIBEIRO, VILMARIA A.
Foram preparados eletrocatalisadores Pt-Sn/C a partir da deposição de Pt sobre Sn/C por diferentes metodologias. Os suportes Sn/C foram preparados pela redução com boroidreto de sódio (BH) e pelo método da redução por álcool (MRA). A deposição da Pt foi efetuada pelo processo de troca galvânica e utilizando agentes redutores pelos métodos BH e MRA. Os materiais obtidos foram caracterizados por energia dispersiva de raios X (EDX), difração de raios X (DRX), microscopia eletrônica de transmissão (TEM), energia dispersiva de raios X de varredura linear (EDX- line scan), voltametria cíclica (VC) e stripping de CO e testados na oxidação eletroquímica do etanol. O difratograma de raios X do Sn/C preparado pelo método BH mostrou a presença da fase Sn metálico, enquanto que, o Sn/C preparado pelo método MRA levou a formação da fase SnO2. Apesar de o material obtido por deposição espontânea apresentar-se mais ativo que o suporte Sn(BH)/C, sua atividade foi inferior ao do catalisador comercial PtSn/C BASF. Os materiais obtidos apresentaram-se mais ativos que o catalisador comercial. A deposição da Pt pelo método BH sobre o suporte Sn(BH)/C levaram a catalisadores com desempenhos inferiores ao catalisador comercial, isto devido a deposição da Pt ocorrer preferencialmente sobre as nanopartículas de Sn metálico, tornando a superfície do catalisador rica em Pt. Os estudos realizados por microscopia eletrônica de transmissão EDX scan-line mostraram que este material apresentou a distribuição mais homogênea dos sítios de Pt e Sn na superfície do catalisador. Assim, nas condições estudadas, a deposição de Pt na superfície do Sn/C, apesar de alguns casos, os materiais obtidos apresentarem melhor atividade que o catalisador PtSn/C comercial, estes apresentaram-se menos ativos que os materiais preparados em uma única etapa por co-redução.
Preparation of PtSn/C electrocatalysts by as alcohol-reduction process using different conditions for ethanol electro-oxidation
2014 - RIBEIRO, V.A.; SEKOL, R.C.; TAYLOR, A.D.; OLIVEIRA NETO, A.; SPINACE, E.V.
Nanocellulose-based carbon prepared by hydrothermal carbonization as support for PtRu nanoparticles for methanol electro-oxidation
2012 - FEIJO, G.G.; SPINACE, M.A.S.; TUSI, M.M.; RIBEIRO, V.A.; LINARDI, M.; OLIVEIRA NETO, A.; SPINACE, E.V.
Preparation of Pt rate earth/C electrocatalysts using the alcohol-reduction process ethanol electro-oxidation
2008 - RODRIGUES, RITA M. de S.; RIBEIRO, VILMARIA A.; BRANDALISE, MICHELE; TUSI, MARCELO M.; LINARDI, MARCELO; FORBICINI, CHRISTINA A.L.G.O.; SPINACE, ESTEVAM V.; OLIVEIRA, ALMIR
Preparacao de eletrocatalisadores PtRuNi/C pelo metodo da reducao por alcool para aplicacao na oxidacao direta de metanol em celulas a combustivel
2008 - RIBEIRO, VILMARIA A.; OLIVEIRA NETO, ALMIR; LINARDI, MARCELO; SPINACE, ESTEVAM V.
Estudo da formacao SOL/GEL em polipropileno irradiado com raios gama
2005 - RIBEIRO, V.A.; GRILLO, P.S.S.; YOSHIGA, A.; ARTEL, B.W.H.; PARRA, D.F.; LUGAO, A.B.; OTAGURO, H.
Estudo da blenda polipropileno/polibuteno submetida a radiacao ionizante
2005 - YOSHIGA, A.; OTAGURO, H.; ARTEL, B.W.H.; PARRA, D.F.; RIBEIRO, V.A.; BUENO, N.; LUGAO, A.B.