Partial oxidation of methane on NiO-MgO-ZrO2 catalysts

Catalysts containing mixtures of NiO, MgO and ZrO2 were synthesized by the polymerization method. They were characterized by X-ray diffraction (XRD), physisorption of N-2 (BET), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES), and then tested in the partial oxidation of methane (POM) in the presence of air (2CH(4):1O(2)) at 750 degrees C for 6 h. Among the ternary oxides, the catalyst with 40 mol% MgO showed the highest conversion rates in the catalytic processes, but also the highest carbon deposition values (48 mmol h (1)). The greater the amount of NiO-MgO solid solution formed, the higher was the conversion rate of reactants (CH4), peaking at 40 mol% of MgO. Catalysts with lower Ni content on the surface achieved a high rate of CH4 conversion into synthesis gas (H-2 + CO). The formation of more NiO-MgO solid solution seemed to inhibit the deactivation of Ni degrees during reaction. The values of the H-2/CO product ratio were generally found to be slightly lower than stoichiometric. (C) 2012 Elsevier Ltd. All rights reserved.

Quimioestratigrafia em basaltos da Formação Serra Geral (Bacia do Paraná) nas regiões centro-oeste de São Paulo e oeste do Paraná: resultados preliminares

A Província Magmática do Paraná-Etendeka, ou ainda Formação Serra Geral assim definida na estratigrafia da Bacia do Paraná, constitui um dos maiores registros vulcânicos em área continental do planeta. O grande volume de magma é evidenciado não só pelas rochas expostas, que contemplam o sul e parte do sudeste brasileiro, mas também pela forte heterogeneidade geoquímica e petrográfica das rochas básicas, intermediárias e ácidas, que integram a placa Sul-Americana. Os trabalhos que abordam a caracterização geoquímica dos diferentes tipos de magmas, obtidos por meio de coleta sistemática de superfície são bastante abundantes, porem pouco são aqueles que abordam a quimioestratigrafia dos basaltos por meio de poços de sondagem buscando as relações estratigráficas aplicadas ao entendimento da evolução dos diferentes tipos de magmas, fontes, intervalo de idades e variações petrográficas sem a influência direta de falhas tectônicas que interferiam no aspecto fidedigno dos dados. Com isso, este trabalho em andamento, com 15 sequencias vulcânicas completas obtidas por meio de poços de sondagem nos estados de São Paulo e Paraná, com até 1156 metros de espessura, são investigados para elementos maiores, traços, terras-raras, isótopos (Pb, Sr e Nd) e idades (Ar-Ar) buscando a compreensão de processos de diferenciação magmática in situ e até mesmo considerações sobre o grau de fusão, fontes mantélicas envolvidas, correlação com a parte sul da província magmática e relação com a fase rifte da placa sul-americana. Os resultados, ainda que preliminares, mostraram que a média da espessura de cada pulso magmático é de 35 metros de rocha basáltica variando de 2 até 90 metros, sendo que a pilha mais profunda alcança 970 metros na região noroeste do estado de São Paulo podendo chegar até 1200 se for considerado a espessura dos sills intrudidos nos sedimentos paleozoicos sotopostos. Já os dados geoquímicos mostraram que as regiões investigadas são compostas exclusivamente por basaltos toleíticos do tipo alto-Ti, com concentrações em TiO2 variando entre 1,77% e 3,66% e MgO de 2,88% até 4,95%, podendo ser divididos em dois subtipos distintos, denominados de Pitanga e Paranapanema conforme classificação de Peate et al. (1992). O primeiro está enriquecido em Nb (8%), K (9%), La (11%), Ce (18%), P (8%), Nd (20%), Zr (19%), Sm (17%), Eu (15%) e Ti (15%) em relação ao segundo. Também é possível verificar que os magmas se alternam na posição estratigráfica sendo iniciado pelo tipo Pitanga (em contato direto com os arenitos eólicos da Formação Botucatu) seguindo pelo magma Paranapanema onde o primeiro, em espessura, e dominante em 60% em relação ao segundo. Por fim, mesmo que o trabalho ainda esteja em fase inicial, é possível concluir que os basaltos investigados podem ter sido abastecidos por mais de uma câmara magmática, que extravasaram suas lavas em épocas distintas, iniciando com basaltos do tipo Pitanga, em contato com os arenitos da Formação Botucatu, e encerrando a pilha edificada com aqueles do tipo Paranapanema.

Steam reforming of ethanol for hydrogen production on Co/CeO²-ZRO² catalysts prepared by polymerization method

Catalysts containing 10%Co supported on CexZr1-xO2 (0 < x < 1) were applied to ethanol steam reforming reactions. The catalysts were characterized by Raman spectroscopy, XANES-H-2 and DRS-UV-Vis. The catalytic tests were conducted at 673, 773 and 873 K, with molar ratios of H2O:ethanol = 3:1. The ethanol conversion and H-2 selectivity were temperature dependent and the association of CeO2 with ZrO2 in the support led to show a low formation of CO, due to the higher mobility of oxygen. (C) 2012 Elsevier B.V. All rights reserved.

Direct Access to Oxidation-Resistant Nickel Catalysts through an Organometallic Precursor

The synthesis of nickel catalysts for industrial applications is relatively simple; however, nickel oxidation is usually difficult to avoid, which makes it challenging to optimize catalytic activities, metal loadings, and high-temperature activation steps. A robust, oxidation-resistant and very active nickel catalyst was prepared by controlled decomposition of the organometallic precursor [bis(1,5-cyclooctadiene)nickel(0)], Ni(COD)(2), over silica-coated magnetite (Fe3O4@SiO2). The sample is mostly Ni(0), and surface oxidized species formed after exposure to air are easily reduced in situ during hydrogenation of cyclohexene under mild conditions recovering the initial activity. This unique behavior may benefit several other reactions that are likely to proceed via Ni heterogeneous catalysis.

EFFECTS OF ADDING LANTHANUM TO Ni/ZrO2 CATALYSTS ON ETHANOL STEAM REFORMING

EFFECTS OF ADDING LANTHANUM TO Ni/ZrO2 CATALYSTS ON ETHANOL STEAM REFORMING. The catalytic performance of Ni/ZrO2 catalysts loaded with different lanthanum content for steam reforming of ethanol was investigated. Catalysts were characterized by BET surface area, X-ray diffraction, UV-vis spectroscopy, temperature programmed reduction, and X-ray absorption fine structure techniques. Results showed that lanthanum addition led to an increase in the degree of reduction of both NiO and nickel surface species interacting; with the support, due to the higher dispersion effect. The best catalytic performance at 450 degrees C was found for the Ni/2LZ catalyst, which exhibited an effluent gaseous mixture with the highest H-2 yield.

Preparation, structural characterization and catalytic properties of Co/CeO2 catalysts for the steam reforming of ethanol and hydrogen production

In this paper, Co/CeO2 catalysts, with different cobalt contents were prepared by the polymeric precursor method and were evaluated for the steam reforming of ethanol. The catalysts were characterized by N-2 physisorption (BET method), X-ray diffraction (XRD), UV-visible diffuse reflectance, temperature programmed reduction analysis (TPR) and field emission scanning electron microscopy (FEG-SEM). It was observed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. Physical-chemical characterizations revealed that the cobalt content of the catalyst influences the metal-support interaction which results in distinct catalyst performances. The catalyst with the highest cobalt content showed the best performance among the catalysts tested, exhibiting complete ethanol conversion, hydrogen selectivity close to 66% and good stability at a reaction temperature of 600 degrees C. (c) 2012 Elsevier B.V. All rights reserved.

An optimization study of PtSn/C catalysts applied to direct ethanol fuel cell: Effect of the preparation method on the electrocatalytic activity of the catalysts

The aim of this work was to perform a systematic study of the parameters that can influence the composition, morphology, and catalytic activity of PtSn/C nanoparticles and compare two different methods of nanocatalyst preparation, namely microwave-assisted heating (MW) and thermal decomposition of polymeric precursors (DPP). An investigation of the effects of the reducing and stabilizing agents on the catalytic activity and morphology of Pt75Sn25/C catalysts prepared by microwave-assisted heating was undertaken for optimization purposes. The effect of short-chain alcohols such as ethanol, ethylene glycol, and propylene glycol as reducing agents was evaluated, and the use of sodium acetate and citric acid as stabilizing agents for the MW procedure was examined. Catalysts obtained from propylene glycol displayed higher catalytic activity compared with catalysts prepared in ethylene glycol. Introduction of sodium acetate enhanced the catalytic activity, but this beneficial effect was observed until a critical acetate concentration was reached. Optimization of the MW synthesis allowed for the preparation of highly dispersed catalysts with average sizes lying between 2.0 and 5.0 nm. Comparison of the best catalyst prepared by MW with a catalyst of similar composition prepared by the polymeric precursors method showed that the catalytic activity of the material can be improved when a proper condition for catalyst preparation is achieved. (C) 2012 Elsevier B.V. All rights reserved.

The influence of different co-catalysts in Pt-based ternary and quaternary electro-catalysts on the electro-oxidation of methanol and ethanol in acid media

One of the key objectives in fuel cell technology is to reduce Pt loading by the improvement of its catalytic activity towards alcohol oxidation. Here, a sol-gel based method was used to prepare ternary and quaternary carbon supported nanoparticles by combining Pt-Ru with Mo, Ta, Pb, Rh or Ir, which were used as electro-catalysts for the methanol and ethanol oxidation reactions in acid medium. Structural characterization performed by XRD measurements revealed that crystalline structures with crystallites ranging from 2.8 to 4.1 nm in size and with different alloy degrees were produced. Tantalum and lead deposited as a heterogeneous mixture of oxides with different valences resulting in materials with complex structures. The catalysts activities were evaluated by cyclic voltammetry and by Tafel plots and the results showed that the activity towards methanol oxidation was highly dependent of the alloy degree, while for ethanol the presence of a metal capable to promote the break of C-C bond, such as Rh, was necessary for a good performance. Additionally, the catalysts containing of TaOx or PbOx resulted in the best materials due to different effects: the hi-functional mechanism promoted by TaOx and a better dispersion of the catalysts constituents promoted by PbOx. (C) 2012 Elsevier B.V. All rights reserved.

Spin-glass-like behavior of uncompensated surface spins in NiO nanoparticulated powder

Nickel oxide nonoparticles successfully synthesized by a polymer percursor method are studied in this work. The analysis of X-ray powder diffraction data provides a mean crystallite size of 22 +/- 2 nm which is in a good agreement with the mean size estimated from transmission electron microscopy images. Whereas the magnetization (M) vs. magnetic field (H) curve obtained at 5 K is consistent with a ferromagnetic component which coexists with an antiferromagnetic component, the presence of two peaks in the zero-field-cooled trace suggests the occurrence of two blocking process. The broad maximum at high temperature was associated with the thermal relaxation of uncompensated spins at the particle core and the low temperature peak was assigned to the freeze of surface spins clusters. Static and dynamic magnetic results suggest that the correlations of surface spins clusters show a spin-glass-like below T-g = 7.3 +/- 0.1 K with critical exponents zv = 9.7 +/- 0.5 and beta = 0.7 +/- 0.1, which are consistent with typical reported for spin-glass systems. (C) 2012 Elsevier B.V. All rights reserved.

Effect of the relationship between particle size, inter-particle distance, and metal loading of carbon supported fuel cell catalysts on their catalytic activity

The effect of the relationship between particle size (d), inter-particle distance (x(i)), and metal loading (y) of carbon supported fuel cell Pt or PtRu catalysts on their catalytic activity, based on the optimum d (2.5-3 nm) and x(i)/d (>5) values, was evaluated. It was found that for y < 30 wt%, the optimum values of both d and x(i)/d can be always obtained. For y >= 30 wt%, instead, the positive effect of a thinner catalyst layer of the fuel cell electrode than that using catalysts with y < 30 wt% is concomitant to a decrease of the effective catalyst surface area due to an increase of d and/or a decrease of x(i)/d compared to their optimum values, with in turns gives rise to a decrease in the catalytic activity. The effect of the x(i)/d ratio has been successfully verified by experimental results on ethanol oxidation on PtRu/C catalysts with same particle size and same degree of alloying but different metal loading. Tests in direct ethanol fuel cells showed that, compared to 20 wt% PtRu/C, the negative effect of the lower x(i)/d on the catalytic activity of 30 and 40 wt% PtRu/C catalysts was superior to the positive effect of the thinner catalyst layer.

Development of Plurimetallic Electrocatalysts Prepared by Decomposition of Polymeric Precursors for EtOH/O-2 Fuel Cell

This work aimed to develop plurimetallic electrocatalysts composed of Pt, Ru, Ni, and Sn supported on C by decomposition of polymeric precursors (DPP), at a constant metal: carbon ratio of 40:60 wt.%, for application in direct ethanol fuel cell (DEFC). The obtained nanoparticles were physico-chemically characterized by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). XRD results revealed a face-centered cubic crystalline Pt with evidence that Ni, Ru, and Sn atoms were incorporated into the Pt structure. Electrochemical characterization of the nanoparticles was accomplished by cyclic voltammetry (CV) and chronoamperometry (CA) in slightly acidic medium (0.05 mol L-1 H2SO4), in the absence and presence of ethanol. Addition of Sn to PtRuNi/C catalysts significantly shifted the ethanol and CO onset potentials toward lower values, thus increasing the catalytic activity, especially for the quaternary composition Pt64Sn15Ru13Ni8/C. Electrolysis of ethanol solutions at 0.4 V vs. RHE allowed determination of acetaldehyde and acetic acid as the main reaction products. The presence of Ru in alloys promoted formation of acetic acid as the main product of ethanol oxidation. The Pt64Sn15Ru13Ni8/C catalyst displayed the best performance for DEFC.

Ruthenium(II) complexes with 2-(diphenylphosphinomethyl)aniline

2-(Diphenylphosphinomethyl)aniline. H2L1, reacts with [RuCl2(PPh3)(3)] to yield the monomeric complexes [RuCl2(H2L1)(PPh3)(CH3CN)], [RuCl2(H2L1)(2)]and the chloro-bridged dimer [(H2L1)(PPh3)Ru(mu-Cl)(2)Ru(PPh3) (H2L1)] depending on the conditions applied. Exclusively the monochelate [RuCl2 (H2L1)(dmso)(2)] is formed during reactions of H2L1 with [RuCl2(dmso)(4)]. H2L1 acts as a neutral, bidentate ligand in all complexes. The products are studied spectroscopically and by X-ray diffraction. (C) 2012 Elsevier Ltd. All rights reserved.

Influence of Modifications to the Pechini Method on the Electroactivity and Stability of Pt-RuOx/C Catalysts

Since electrode electroactivity and stability depend directly on the nature, morphology, and structure of the material, we have investigated how modifications to the Pechini method during the synthesis of Pt-RuOx/C electrocatalysts affected catalyst activity. The structure and stability of the resulting materials were investigated after their submission to a large number of potential scans and to constant potential for a prolonged time period in sulfuric acid 0.5 mol L-1 and methanol 0.1 mol L-1 solution. DMFC tests were accomplished using membrane electrode assemblies (MEAs) prepared by hot-pressing a pretreated Nafion 117 membrane together with the prepared Pt-RuOx anodes and a Pt cathode (from E-TEK), in order to compare the catalytic activity of the materials prepared by different methods. The stability studies demonstrated that the catalyst whose resin/carbon support mixture was agitated in a balls mill before undergoing heat-treatment was more stable than the other prepared catalysts. The catalysts synthesized with the single resin consisting of Pt and Ru and subjected to ultrasound before heat-treatment furnished the highest power density in the single fuel cell. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.011208jes]

CuO-CeO2 catalysts synthesized in one-step: Characterization and PROX performance

PEM fuel cells seem to be the most affordable and commercially viable hydrogen-based cells, the biggest challenge being to obtain CO-free H-2 (<100 ppm) as the fuel. In this study, the use of CuO-CeO2 catalysts in preferential oxidation of CO to obtain CO-free H-2 (PROX reaction) was investigated. Ce1-xCuxO2 catalysts, with x (mol%) = 0, 0.01, 0.03, 0.05 and 0.10, were synthesized in one-step by the polymeric precursor method, to obtain a very fine dispersion and strong metal-support interaction, to favor active copper species and a preference for the PROX reaction. The results obtained from catalyzed reactions and characterization of the catalysts by XRD, Rietveld refinement, BET surface area, UV-Vis and TPR, suggest that this one-step synthesis method gives rise to catalysts with copper species selective for the PROX reaction, which reaches a maximum rate on Ce0.97Cu0.03O2 catalyst. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Ethanol steam reforming over rhodium and cobalt-based catalysts: Effect of the support

The effect of support on the properties of rhodium and cobalt-based catalysts for ethanol steam reforming was studied in this work, by comparing the use of magnesia, alumina and Mg-Al oxide (obtained from hydrotalcite) as supports. It was found that metallic rhodium particles with around 2.4-2.6 nm were formed on all supports, but Mg-Al oxide led to the narrowest particles size distribution; cobalt was supposed to be located on the support, affecting its acidity. Rhodium interacts strongly with the support in the order: alumina> Mg-Al oxide > magnesia. The magnesium-containing catalysts showed low ethene selectivity and high hydrogen selectivity while the alumina-based ones showed high ethene selectivity, assigned to the Lewis sites of alumina. The Mg-Al oxide-supported rhodium and cobalt catalyst was the most promising sample to produce hydrogen by ethanol reforming, showing the highest hydrogen yield, low ethene selectivity and high specific surface area during reaction. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.