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Ordered intermetallic compounds of Pt-based metal electrocatalysts have been recently proposed as very efficient anode materials for reactions involved in low temperature fuel cells. In this work, supported ordered intermetallics nanoparticles PtSn/C and PtSb/C and supported platinum nanoparticles (Pt/C) were prepared at low temperature from their metallic precursors by a modified polyol process, using tetraethylene glycol as the solvent and reducing agent and Vulcan carbon XC-72 as the support. Powder X-ray diffraction patterns confirmed the presence of the ordered intermetallic phase and furnished lattice parameters and crystal structure. Transmission electron microscopy images show that the metal particles were highly dispersed and distributed homogeneously over the support, and energy-dispersive X-ray spectroscopy showed that the composition of the final product is within that of the desired stoichiometry. The electrocatalytic activity of these intermetallic phases toward the oxidation of methanol, ethanol, and ethylene glycol were confirmed by cyclic voltammetry and steady-state polarization curve at room temperature. The results showed that the supported intermetallic nanoparticles PtSn and PtSb are more active than the Pt/C catalyst prepared by the same method for alcohol oxidation.

Recebido em 28/07/2015; aceito em 22/12/2015; publicado na web em 11/03/2016ZnO and Ag-ZnO were synthesized in a simple and efficient manner by thermal decomposition of zinc oxalate and silver/zinc mixed oxalate. The influence of the addition of metallic silver on ZnO particles and the effect of temperature in the thermal treatment were investigated. The samples were characterized by thermogravimetric analysis, Raman, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, specific surface area (Brunauer-Emmett-Teller) and diffuse reflectance spectroscopy. The photocatalytic activity of these materials in the decolorization of direct red 23 diazo dye was studied. The complete conversion into oxides from oxalates at lower temperatures was determinant in the photocatalytic efficiency of both the oxides. The presence of silver in zinc oxide, treated at 400 °C, more than doubled the rate constant of diazo dye decolorization (6.87×10-3 min -1) with respect to ZnO, treated at 600 °C, resulting in 3.07×10 -3 min -1 under UV irradiation at 30 °C.

RESUMOO objetivo do estudo foi avaliar o efeito da qualidade de madeiras de eucalipto no desempenho da polpação kraft sob duas diferentes condições de polpação e em dois níveis de deslignificação, baseando-se no rendimento, alvura, viscosidade e índice k/kappa corrigido das polpas produzidas. As madeiras de eucalipto (A, B e C), foram analisadas quanto às suas propriedades físico-químicas (densidades básica e aparente, teor de ligninas insolúvel e solúvel, teor de extrativos, cinzas e cinzas insolúveis em ácido clorídrico) e utilizadas para a produção de polpa celulósica por meio do cozimento kraft modificado, utilizando duas condições de polpação, sendo elas: Condição I (PI) -álcali efetivo de 16,5%, sulfidez de 30% e temperatura de cozimento de 155ºC; e Condição II (PII) -álcali efetivo de 17,5%, sulfidez de 32% e temperatura de cozimento de 147ºC. Ambos os cozimentos foram realizados buscando-se no número kappa de 15,5 ± 0,5 e de 18,0 ± 0,5. Foram avaliados os seguintes parâmetros de polpação e propriedades das polpas produzidas: fator H, rendimento depurado, viscosidade, alvura, conteúdo de ácidos hexenurônicos e o índice k/kappa corrigido. A madeira A, que apresentou menores teores de extrativos e lignina em sua constituição, bem como menores densidades básica e aparente quando comparada com as madeiras B e C, apresentou os melhores resultados para os parâmetros de cozimento avaliados, com destaque para a polpa produzida pela condição de cozimento PII com o número kappa de (18,0 ± 0,5), que apresentou maior rendimento, alvura e viscosidade dentre todas as polpas produzidas. Polpas produzidas com maior número kappa apresentam menores índices k/kappa corrigidos. Palavras-chave: Eucalyptus; qualidade da madeira; grau de deslignificação; condições de polpação kraft. ABSTRACTThe aim of this study was to evaluate the wood quality in the kraft pulping performance under two different pulping conditions at two delignification degrees based on results for the yield, brightness, viscosity, and k/ kappa corrected index. Eucalyptus wood (A, B, and C) was analyzed about their physicochemical properties (basic and apparent density, insoluble and soluble lignin content, extractive content, ash and insoluble ash in hydrochloric acid) and used for pulp production by modified kraft cooking, using two different pulping conditions: Condition I (PI) -16.5% effective alkali, 30% sulfidity, and 155º of cooking temperature; and Condition II (PII) -17.5% effective alkali, 32% sulfidity,and 147ºC cooking temperature. Both conditions were performed to kappa number 15.5 ± 0.5 and 18.0 ± 0.5. The following pulping parameters and pulp properties produced were evaluated: H factor, screened yield, viscosity, brightness, hexenuronic acid content, and the k/kappa corrected index. The A wood, which had lower extractives and lignin content in its constitution, as well as lower basic and apparent density when compared with B and C woods, showed good results for cooking parameters, especially the pulp produced at PII condition at kappa number 18...