JULIO CESAR M. DA SILVA

JULIO CESAR M. DA SILVA

Página do item completo

Resultados de Busca

Agora exibindo 1 - 10 de 66

One-step synthesis of AuCu/TiO2 catalysts for CO preferential oxidation
2020 - ALENCAR, CATARINE S.L.; PAIVA, ANA R.N.; SILVA, JULIO C.M. da; VAZ, JORGE M.; SPINACE, ESTEVAM V.
Au/TiO2 (1wt% Au), Cu/TiO2 (1wt% Cu) and AuCu/TiO2 (1wt% AuCu) catalysts with different Au:Cu mass ratios were prepared in one-step synthesis using sodium borohydride as reducing agent. The resulting catalysts were characterized by X-ray diffraction (XRD), X-ray Dispersive Energy (EDX), Transmission Electron Microscopy (TEM) and Temperature Programmed Reduction (TPR) and tested for the preferential oxidation of carbon monoxide (CO-PROX reaction) in H2-rich gases. EDS analysis showed that the Au contents are close to the nominal values whereas for Cu these values are always lower. X-ray diffractograms showed only the peaks of TiO2 phase; no peaks of metallic Au and Cu species or oxides phases were observed. TPR and high-resolution TEM analysis showed that AuCu/TiO2 catalysts exhibited most of Au in the metallic form with particles sizes in the range of 3-5 nm and that Cu was found in the form of oxide in close contact with the Au nanoparticles and well spread over the TiO2 surface. The AuCu/TiO2 catalysts exhibited good performance in the range of 75-100 °C and presented a better catalytic activity when compared to the monometallic ones. A maximum CO conversion of 98.4% with a CO2 selectivity of 47% was obtained for Au0.50Cu0.50/TiO2 catalyst at 100°C.
Fuel cell and electrochemical studies of the ethanol electro-oxidation in alkaline media using PtAuIr/C as anodes
2018 - SILVA, SIRLANE G.; FONTES, ERIC H.; SILVA, JULIO C.M.; ASSUMPÇAO, MONICA H.M.T.; OLIVEIRA NETO, ALMIR; LINARDI, MARCELO
The use of fossil fuels has resulted in an increase of CO2 concentration in the atmosphere . It is well known that CO2 emission from fossil fuels is one of the principals responsible for the greenhouse effect. Taking these aspects into account,fuel cells might bean excelente alternative to the current energy generation as a clean and eficiente power source. In this context, alkaline fuel cells have attracted worldwide attention due to its promise to produce clean energy with high efficiency [1], thus direct etanol fuel cell could offer an alternative for electrical energy generation. In this work, ethanol electrooxidation reaction was investigated considering conventional electrochemical experiments in alkaline media, direct ethanol fuel cell (DEFC), and in situ ATRFTIR. The working electrode/anodes were composed of monometallic Pt/C, Au/C, Ir/C, and trimetallic PtAuIr/C nanoparticles with atomic Pt/Au/Ir ratios of 40:50:10, 50:40:10, 60:30:10, 70:20:10, and 80:10:10. X-ray diffraction (XRD) suggests PtAuIr/C alloy formation, and according to transmission electron micrographs, the mean particle sizes are from 4 to 6 nm for all catalyst compositions. PtAuIr/C 40:50:10 showed the highest catalytic activity for ethanol electro-oxidation in the electrochemical experiments; using this material, the peak current density from ethanol electro-oxidation on cyclic voltammetry experimente was 50 Ma per g of Pt, 3.5 times higher than that observed with Pt/C. The fuel cell performance was superior using all PtAuIr/C compositions than using Pt/C. Au/C and Ir/C presented very poor catalytic activity toward etanol electro-oxidation. The improved results obtained using PtAuIr/C might be related to the OHads species formed at low overpotential on Ir and to the decrease on adsorption energy of poisoning intermediates on Pt sites, promoted by Au.
Electrocatalysts for direct ethanol fuel cells
2018 - SILVA, JULIO C.M. da; LOPES, THIAGO; OLIVEIRA NETO, ALMIR; SPINACE, ESTEVAM V.
In this chapter, an overview of electro-catalysts for direct ethanol fuel cells based on polymer electrolyte membranes is presented, with special attention given to the alkaline anion exchange membrane-based devices. Considering the anodic reaction, it is evidenced that a substantial effort has been dedicated towards increasing the fuel cell efficiency by developing electrocatalysts with higher catalytic activity. In this sense, palladium is pointed out as a promising substitute to platinum with regards to electrocatalytic activity, price and element availability. Furthermore, palladium-based nanoparticles are pointed out as the electrocatalysts with the highest electrocatalytic activity for ethanol electro-oxidation in alkaline media. Taking into account the support materials for the electrocatalysts nanoparticles, it was possible to observe an evolution in carbon-based materials, first carbon nanotubes overcame the carbon black, where more recently, graphene is addressed as the best support choice for catalysts nanoparticles. Different efforts have been made to improve the properties of the support materials, such as doping with nitrogen or with metal oxides like TiO2, for example. Considering the cathode materials, the main goal is to develop catalysts with enhanced activity to the oxygen reduction reaction as well as tolerance to ethanol molecules that crossover the electrolyte membrane.
Preparação de catalisadores de níquel e cério suportados em carvão de coco
2018 - FERREIRA, JOAO C.; CAVALLARI, ROGER V.; SILVA, FELIPE A. e; RODRIGUES, THENNER S.; SILVA, JULIO C.M.; BERGAMASCHI, VANDERLEI S.
O carvão de coco foi ativado pelo processo hidrotermal assistido por microondas (HMO) usando ácido nítrico (2,42 M) nas condições de temperatura de 120 ºC, patamar de 45 minutos, rampa de aquecimento de 10 ºC min-1 e pressão de 3,0 kgf / cm2. Na caracterização usaram-se métodos analíticos como: espectroscopia Raman, medidas de área superficial (BET), análise térmica (TG), difração de raios X (DRX), microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva (EDS) e redução à temperatura programada (TPR). Os catalisadores foram avaliados na reforma a vapor do etanol objetivando a formação de hidrogênio. Foram observadas boas atividades catalíticas com conversão completa do etanol e formação predominante de produtos de reforma (H2 e CO2) e CO e CH4 como subprodutos e em baixas concentrações, indicando uma boa seletividade e estabilidade para a reação de reforma a vapor do etanol com a manutenção total de atividade mesmo após 24 horas de reação a 550 °C.
Preparação de suporte de catalisador a partir de biocarbono
2018 - CAVALLARI, ROGER V.; DE LIMA, NATASHA B.; SILVA, JULIO C.M.; BERGAMASHI, VANDERLEI S.; FERREIRA, JOAO C.
O uso exagerado de recursos não renováveis, nas ultimas décadas, deflagrou consequências negativas para a sociedade, havendo necessidade de buscar soluções diante dos efeitos deletérios causados pelo avanço da devastação do meio ambiente. Visando contribuir com a ampliação das estratégias de controle de poluentes através do desenvolvimento de tecnologia de baixo custo, o presente trabalho tem como objetivo principal o desenvolvimento de materiais ativos com elevada resistência térmica e boa área especifica para adsorção e impregnação de metais. Neste sentido foram estudados três rotas de tratamento do biocarvão. Na caracterização do biocarbono usaram-se métodos analíticos como: Espectroscopia de Infravermelho (IV), Espectroscopia RAMAM, Medida da Área Superficial (BET), Análise Térmica (TG), Difração de Raios X (DRX) e Microscopia Eletrônica de Varredura (MEV). As diferentes condições de tratamento resultaram em mudanças na estrutura carbonácea do biocarbono com características adequadas para serem utilizados como suporte em catalisadores, apresentando sítios ativos com cargas negativamente carregadas para promover a fixação de metais em sua superfície. Verificou-se também um aumento na área superficial específica, variando entre 341,4 a 749,7 m2 g-1 e alterações nas bandas D e G do carvão e uma alta resistência à temperatura, o que promove reações catalíticas com baixa perda de catalisador.
Preparation of Au/TiO2 by a facile method at room temperature for the CO preferential oxidation reaction
2018 - LEAL, GEORGIA B.; CIOTTI, LIGIA; WATACABE, BEATRIZ N.; SILVA, DANIELA C.L. da; ANTONIASSI, RODOLFO M.; SILVA, JULIO C.M.; LINARDI, MARCELO; GIUDICI, REINALDO; VAZ, JORGE M.; SPINACE, ESTEVAM V.
A simple strategy was used to prepare Au/TiO2 catalyst at room temperature. Au nanoparticles were initially prepared in solution using HAuCl4.3H2O as Au precursor, sodium citrate as stabilizing agent and sodium borohydride as reducing agent. The preformed Au nanoparticles were further supported on TiO2 and the resulting solid material was characterized by Energy-dispersive X-ray spectroscopy, X-ray diffraction and Transmission Electron Microscopy and tested for the preferential oxidation of carbon monoxide in hydrogen-rich stream (COPROX reaction). The obtained Au/TiO2 catalyst consisted of Au nanoparticles with an average size of ~ 4 nm and showed excellent catalytic performance in the 20-50 °C low-temperature range. In particular, at 40 °C a CO conversion of 99.5% and CO2 selectivity of 45% were obtained using an O2/CO ratio of 2 (1 vol% CO, λ=4) and 97 vol% H2 in the feed gas stream (GHSV=15,000 mL gcat −1 h−1).
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.
Iridium-rhodium nanoparticles for ammonia oxidation
2017 - SILVA, JULIO C.M.; ASSUMPÇAO, MONICA H.M.T.; HAMMER, PETER; O. NETO, ALMIR; SPINACE, ESTEVAM V.; BARANOVA, ELENA A.
This study reports the use of carbon-supported IrRh/C electrocatalysts with different iridium-to-rhodium atomic ratios (0 : 100, 50: 50, 70: 30, 90: 10, and 100: 0) for ammonia electro-oxidation (AmER) in alkaline media. The materials prepared by using the sodium borohydride method showed a mean diameter of 4.5, 4.8, 4.2, and 4.5 nm for Ir/C, Ir90Rh10/C, Ir70Rh30/C, and Ir50Rh50/C, respectively. According to electrochemical and fuel cell experiments, the Ir50Rh50/C catalyst was the most promising towards AmER. This catalyst, which consisted predominantly of the metallic Ir/Rh phases, showed a 500% higher current density and 55% higher maximum power than that obtained for Ir/C. After 8 h galvanostatic electrolysis, 93% of initial ammonia was degraded when using Ir50Rh50/C, whereas it was only 70% with Ir/C. The high activity of the Ir50Rh50/C is attributed to a synergic effect of two metals at this iridium-to-rhodium ratio, which enhances the kinetics of AmER contributing towards ammonia dehydrogenation at lower potentials.
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.
Carbon-supported Pt nanoparticles with (100) preferential orientation with enhanced electrocatalytic properties for carbon monoxide, methanol and ethanol oxidation in acidic medium
2017 - ANTONIASSI, R.M.; SILVA, J.C.M.; LOPES, T.; OLIVEIRA NETO, A.; SPINACE, E.V.
The relationship between atomic arrangement (morphology) and catalytic activity/selectivity in heterogeneous catalysis is an actual hot research topic concerning a range of reactions. This article evaluates one-pot synthesized carbon-supported Pt nanoparticles with preferential Pt(100) orientation prepared with an environmentally friendly shape-directing agent and compares this with Pt/C polycrystalline towards CO, methanol and ethanol electrooxidation reactions. The preferentially cubic nanomaterial (Pt-(100)) interacts differently with CO molecule and presents distinct hydrogen adsorption/desorption characteristics. Pt/C polycrystalline exhibits a CO-stripping profile with one peak at 0.86 V in contrast to three peaks between 0.75 and 0.86 V and a pre-peak at about 0.40.6 V for the Pt/C-(100), which may be associated to the unique surface characteristics of the cubic material. The onset potentials towards carbon monoxide, methanol and ethanol electro-oxidation reactions on Pt/C-(100) are 22%, 21% and 54% lower than on Pt/C polycrystalline. The ratio between the forward per backward peak current densities for the electrooxidation of ethanol and methanol are higher on Pt/C-(100), which suggests that Pt(100) domains are more tolerant to undergo poisoning by the intermediates/by-products formed in these reactions. Proton exchange membrane fuel cells fed with pure hydrogen and with a H-2/CO mixture show superior performance using Pt/C-(100) as anode in comparison to Pt/C polycrystalline catalyst. These results evidence that controlling the morphology of Pt nanoparticles is a key factor to improve the catalytic activity of the polymer electrolyte fuel cell fueled with fuels that involve the electro-oxidation of CO.