Resumen El NiO es útil en la producción de sensores electroquímicos y para la obtención de níquel metálico, el cual es usado como catalizador para producir hidrogeno a partir de gas natural. En este trabajo, se sintetizaron hidrotalcitas a base de níquel-aluminio y níquel-zinc-aluminio, las cuales fueron calcinadas a 500 oC y estudiadas por diferentes técnicas instrumentales. Se observó que las hidrotalcitas a base de níquel y aluminio son más estables térmicamente, colapsando a temperaturas más altas que aquellas conteniendo zinc. Durante el proceso de calcinación el aluminio se incorpora en la red cristalina del NiO, disminuyendo los parámetros cristalográficos de este óxido. La adición de zinc disminuye este efecto, contribuyendo además con la formación de partículas más pequeñas del NiO. Adicionalmente el aluminio distorsiona la red del NiO, efecto que es minimizado por el zinc, dificultando la incorporación de Al3+ en la red cubica del NiO.

Abstract NiO has a variety of applications, mainly in the production of electrochemical sensors and of metallic nickel. In addition, it is widely used as catalysts to produce hydrogen from natural gas. In this work, hydrotalcites based on nickel-aluminum and nickel-zinc-aluminum were synthesized, calcined at 500 °C and studied by different techniques. It was observed that nickel-aluminum hydrotalcites are thermally more stable, collapsing at higher temperatures than hydrotalcites containing zinc. During calcination, aluminum is incorporated into NiO lattice, leading to a decrease in crystallographic parameters. However, zinc decreases this effect, favoring the formation of NiO with lattice parameters close to pure nickel oxide. Zinc also contributes to the formation of smaller NiO particles, which is very useful for its use as a catalyst. In addition, aluminum led to a distortion in NiO lattice, an effect that is minimized by zinc, showing that it hinders the incorporation of Al3+ in the NiO lattice.

ABSTRACT Films of lanthanum strontium manganite, LSM (La0.8Sr0.2MnO3) were deposited on yttria stabilized zirconia (YSZ) substrates by different methods aiming to establish the most suitable route to prepare cathodes for solid oxide fuel cells (SOFC). Samples were obtained by using a solution of lanthanum, strontium and manganese nitrates or a dispersion of the LSM powder in this solution. Both commercial and synthetized LSM powders were used, the last one obtained by amorphous citrate method. The films were deposited by spray pyrolysis on YSZ substrates prepared by uniaxial and isostatic pressing. Samples were characterized by scanning electron microscopy, confocal laser scanning microscopy, X-ray diffraction and two-probe conductivity measurements. The area specific resistance and relaxation to cathodic activation were measured by electrochemical impedance spectroscopy. The substrate obtained by uniaxial pressing and the commercial LSM produced films with the highest amount of surface cracks. The film obtained from the suspension showed area specific resistance and activation energy lower than the other produced from the solution. For both samples, the cathodic activation process resulted in an initial reduction of the total resistance of around 20%, the sample produced from the suspension being more resistant to relaxation. Therefore, the LSM suspension is more suitable than the salts solution for preparing films by spray pyrolysis on YSZ substrates to obtain efficient cathodes for SOFC.

ABSTRACT The solid oxide fuel cells (SOFC) enable the efficient generation of clean energy, fitting the current requirements of the growing demand for electricity and for the environment preservation. When powered with biogas (from digesters of municipal wastes), the SOFCs also contribute to reduce the environmental impact of these wastes. The most suitable route to produce hydrogen inside SOFC from biogas is through dry reforming but the catalyst is easily deactivated by coke, because of the high amounts of carbon in the stream. A promising way to overcome this drawback is by adding a second metal to nickel-based catalysts. Aiming to obtain active, selective and stable catalysts for biogas dry reforming, solids based on nickel (15%) and copper (5%) supported on aluminum and magnesium oxide were studied in this work. Samples were prepared by impregnating the support with nickel and copper nitrate, followed by calcination at 500, 600 and 800 oC. It was noted that all solids were made of nickel oxide, nickel aluminate and magnesium aluminate but no copper compound was found. The specific surface areas did not changed with calcination temperature but the nickel oxide average particles size increased. The solids reducibility decreased with increasing temperature. All catalysts were active in methane dry reforming, leading to similar conversions but different selectivities to hydrogen and different activities in water gas shift reaction (WGSR). This behavior was assigned to different interactions between nickel and copper, at different calcination temperatures. All catalysts were active in WGSR, decreasing the hydrogen to carbon monoxide molar ratio and producing water. The catalyst calcined at 500 oC was the most promising one, leading to the highest hydrogen yield, besides the advantage of being produced at the lowest calcination temperature, requiring less energy in its preparation.

Nos últimos tempos, a intensa atividade humana levou a um aumento de resíduos agrícolas no meio ambiente. Visando a encontrar novas aplicações para estes materiais estudou-se, neste trabalho, o efeito do teor de ferro (2.5, 5, 10 e 15%) sobre as propriedades catalíticas de óxido de ferro suportado em carvão ativado, preparado a partir de cascas de coco. O teor de ferro afetou as propriedades texturais e redutoras dos sólidos. Detectou-se hematita na amostra mais pobre em ferro e magnetita com um núcleo de hematita nas demais. Estes catalisadores foram eficazes na remoção do azul de metileno em soluções aquosas por adsorção e pela reação de Fenton. O sólido com 15% de ferro foi o mais ativo, provavelmente devido à maior quantidade de sítios ativos na superfície. Estes catalisadores são ambientalmente amigáveis, contribuindo para a redução de resíduos sólidos no meio ambiente e purificação de efluentes têxteis, preservando os recursos hídricos.

In recent times, the intense human activity has led to an increase of the agriculture wastes in the environment. "In order to find new applications for these materials, the effect of iron content (2.5, 5, 10 and 15%) on the catalytic properties of activated carbon-supported iron oxide, prepared from coconut shells, was studied. The iron amount affected the textural and reducing properties of the solids and particle sizes. Hematite was found for the most iron-poor sample, while particles of magnetite with a core of hematite were found for the others. These catalysts were effective in the methylene blue removal from aqueous solutions by adsorption and Fenton reaction. The solid with 15% of iron was the most active one probably due to the highest iron amount on the surface. These catalysts are environmentally friendly, contributing to the decrease of the solid wastes in the environment as well as to purify textile effluents, preserving water resources.

This review presents the main characteristics and properties of microporous (zeolites) and ordered mesoporous materials, focusing on structural aspects and preparation. In addition, their use as heterogeneous catalysts are also discussed, with emphasis on their advantages and disadvantages. Due to difficulty in application of zeolites in the conversion of bulky molecules, the most relevant strategies of synthesis for the preparation of zeolitic materials with hierarchical pore structure was also analyzed, which allow this limitation to be overcome.

El uso del hidrógeno para la generación de energía ha renovado el interés por la reacción WGS. Los catalizadores usados para acelerar esta reacción requieren condiciones especiales de reducción, lo que dificulta su aplicación en celdas combustibles para la producción de energía. En este trabajo se sintetizaron catalizadores de níquel soportado en óxido de cinc o aluminio usando un diseño factorial 3² en el caso de los materiales con cinc. Los resultados obtenidos se emplearon en la síntesis de sólidos trimetálicos de níquel, cinc y aluminio en las condiciones más propicias para garantizar mejor actividad y selectividad. Los sólidos fueron caracterizados por EDX, DRX, TPR y evaluados en la reacción WGS a 260 °C. Se observó la incorporación de los cationes Zn²+ yAl³+ en la red del NiO, lo que disminuye su reducibilidad con hidrógeno. Los materiales que contenían cinc fueron 100% selectivos para la reacción WGS. En la evaluación de los catalizadores con níquel y aluminio hubo formación de metano; sin embargo, este compuesto no fue observado durante la evaluación catalítica de los sólidos trimetálicos. Los catalizadores más activos fueron aquellos calcinados en temperaturas más bajas y con las menores cantidades de cinc.

The use of hydrogen for power generation has again awaken the interest in the WGS reaction. The catalysts used to accelerate this reaction need special conditions of reduction. This limits their application in fuel cells for energy production. In this work, nickel catalysts-supported in zinc oxide or aluminum oxide were synthesized by using a 3² factorial design with materials containing zinc. The results were used for the synthesis of trimetallic solid containing nickel, zinc and aluminum, in the most favorable conditions to ensure high activity and selectivity. The solids were characterized by EDX, XRD, TPR and evaluated in the WGS reaction at 260 °C. The incorporation of Zn2+ and Al3+ cations was observed in the lattice of NiO. This phenomenon affects the reducibility of these materials with hydrogen. The materials containing zinc were of 100 per cent selectivity for the reaction under study. In the case of nickel and aluminum catalysts, methane formation was observed, but this species was not detected in the trimetallic catalysts. The catalytic activity of trimetallic materials is consistent with the trends in bimetallic nickel-zinc or nickel-aluminum materials. The most active catalysts were those calcined at the lowest temperatures with the smallest amounts of zinc.

O uso do hidrogênio para a geração de energia tem renovado o interesse pela reação WGS. Os catalisadores usados para acelerar esta reação requerem condições especiais de redução. Isso dificulta a sua aplicação em células combustíveis para a geração de energia. Neste trabalho se sintetizaram catalisadores baseados em níquel suportado em oxido de zinco ou alumínio, usando um desenho fatorial 3² no caso dos materiais contendo zinco. Os resultados obtidos foram usados para a síntese de sólidos tri-metálicos contendo níquel, zinco e alumínio nas condições ótimas para aumentar a atividade e seletividade dos materiais. Os sólidos foram caracterizados pelas técnicas EDX, DRX, TPR e avaliados na reação WGS a 260 °C. Observou-se a incorporação dos cátions Zn2+ eAl3+ na rede do NiO, o que diminui a redução dos sólidos com hidrogênio. Os sólidos contendo zinco foram 100% seletivos para a reação em estudo. Na avaliação dos catalisadores contendo níquel e alumínio ocorreu a formação de metano, no entanto esta espécie não foi observada na avaliação catalítica dos sólidos tri-metálicos. Os catalisadores mais ativos foram os calcinados nas temperaturas mais baixas e com menores quantidades de zinco.

The nature of gold species in Au/CeX Zr1-X O2 catalysts was successfully investigated using the visible and near infrared photoacoustic spectroscopy and Fourier transform infrared spectroscopy of adsorbed carbon monoxide. It was found that the visible and near infrared photoacoustic spectroscopy is a powerful technique for investigating the changes of gold particle size due to addition of zirconium and the oxidation state of gold particles. It was also noted that the increase of zirconium in the solids makes gold incorporation more difficult due to the electronic shielding caused by zirconium, decreasing the probability of replacing cerium by gold. For the samples studied, the particle size ranged from 20-30 nm and the Au+, Au3+ and Auº species were found in the catalysts.

In recent years nanomaterials, such as metallic nanoparticles, nanowires, nanotapes, nanotubes and nanocomposites, have attracted increasing interest for several technological applications. In catalysis, the great potential of nanomaterials is related to the high catalytic activity exhibited by these materials as a function of the high surface/volume ratio when the particles acquire diameter below 5 nm. In this work, a review about concepts and background of nanoscience and nanotechnology is presented with emphasis in catalysis. Special attention is given to gold nanoparticles and carbon nanotubes, focusing the properties and characteristics of these materials in several catalytic reactions.

Porous carbons have received great attention because of their potential use as adsorbents, sensors, catalytic supports and others. Among the available methods for preparing these solids, the sequential templating emerges as an efficient way to tail carbon materials, with large specific surface areas, high porosity, controlled narrow pore size distribution and different functional groups. The template process is based on the infiltration of carbon precursors into the pores of inorganic frameworks. This work reviews the most important variables involved in the sequential template process to prepare micro, meso and macroporous carbon with tailored properties as well as their applications.

In an effort to minimize the impact on the environment, removal of pollutants, such as phenolic compounds, from the industrial wastewater has great importance nowadays because of the high toxicity and low biodegradability of these compounds. This work discusses the different methods to remove these compounds from industrial wastewater, showing their advantages and disadvantages. Advanced Oxidation Process (AOPs) are presented as a promising technology for the treatment of wastewater containing phenolic compounds. Among the AOPs, photolysis, photocatalysis and the processes based on hydrogen peroxide and on ozone are discussed with emphasis on the combined processes and the oxidation mechanisms.

The activity of copper-doped hematite in the SCR with propane, in the presence of oxygen, was evaluated in this work. It was found that copper sulfate led to the production of solids with different specific surface areas depending on the amount of copper. The sulfur and copper species were mainly located on the surface. The copper-containing catalysts were more active in the reduction of nitrogen oxides and less active in the propane oxidation as compared to pure hematite. This behavior was assigned to an association of both sulfur and copper species to produce new sites active for NO reduction.

Com o desenvolvimento das células a combustível, há uma expectativa de crescimento da demanda por hidrogênio. A reforma a vapor de etanol é mais atrativa que outros processos relacionados para produzir hidrogênio de alta pureza, por apresentar diversas vantagens, tais como a utilização de fontes de energia renovável e facilidade de manuseio e estocagem do etanol. Alguns dos catalisadores usados nesse processo são níquel suportado em óxidos de lantânio, assim como níquel suportado em óxido de magnésio, que apresentam alta atividade e seletividade a hidrogênio e estabilidade. Com o fim de obter catalisadores alternativos para essa reação estudou-se, neste trabalho, o efeito do magnésio nas propriedades de catalisadores baseados em níquel e lantana. As amostras, com 15% Ni e La/Mg (molar)=20, 10 e 5, foram preparadas por precipitação, seguida de impregnação; preparou-se, também, sólidos sem níquel e/ou magnesium para fins de comparação. Nas amostras sem magnésio, foram produzidos hidróxidos e óxidos de lantânio mas nas outras amostras foi formado apenas óxido de lantânio. Por outro lado, os sólidos contendo níquel também produziram o composto La2NiO4. Adicionando-se pequenas quantidades de magnésio ao óxido de lantânio (La/Mg=20, 10), a área superficial específica diminui mas quantidades mais altas (La/Mg=5) não causam variações. Entretanto, a adição do níquel e magnésio levarou a um aumento. Esses resultados foram relacionados às tensões e imperfeições geradas durante a preparação do sólido; nesse caso, supõe-se que o magnésio favorece o aumento do tamanho de partícula enquanto a ação combinada do magnésio e níquel contribui para evitar a sinterização. Todos os sólidos apresentaram sítios básicos na superfície. Pode-se concluir que o método usado neste trabalho pode ser útil para controlar as propriedades estruturais e texturais do óxido de lantânio, permitindo a produção de materiais como propriedades pré-determinadas.

The development of fuel cells comes along with an expected increase in the demand for hydrogen. Ethanol reforming is more attractive than other related processes to produce highly pure hydrogen, since it has several advantages such as the use of renewably energy sources and the easy storage and handling of ethanol. Some of the catalysts used in this process are lanthanum oxide-supported nickel, as well as magnesium oxide-supported nickel, which exhibit high activity, selectivity to hydrogen and excellent stability. In order to find alternative catalysts to this reaction, the effect of magnesium on the properties of nickel and lanthanum-based catalyst was studied in the present work. Samples with 15% Ni and La/Mg (molar)=20, 10 and 5 were prepared by precipitation, followed by impregnation; solids without nickel and/or magnesium waere also obtained for comparison. In the free-magnesium sample, lanthanum oxide and hydroxide were produced but in the other samples only lanthanum oxide was produced. On the other hand, nickel-containing solids also produced the La2NiO4 compound. By adding small amounts of magnesium to solids (La/Mg=20, 10), the specific surface area decreased but higher amounts (La/Mg=5) did not change it. However, the addition of both nickel and magnesium led to an increase of it. These results were related to the stresses and imperfection generated during the solid preparation; in this case, magnesium is supposed to favor the increase of the particle size while the combined action of magnesium and nickel contributes to avoid sinterization. All solids showed basic sites on the surface. It can be concluded that the method used in this work can be useful to control the structural and textural properties of lanthana allowing the production of tailored catalysts.

The alpha-zirconium (IV) hydrogenphosphate (alpha-ZrP) has received great attention in the last years due to its properties like ion exchange, intercalation, ionic conductivity and catalytic activity. This work reports a method to produce metallic copper clusters on alpha-ZrP to be used as catalysts in petrochemical processes. It was found that the solids were non-crystalline regardless of the uptake of copper and the reduction. The specific surface area increased as a consequence of the increase of the interlayer distance to accept the copper ions between the layers. During the reduction, big clusters of copper (0,5-11µ) with different sizes and shapes were produced.

The effect of chromium on the catalytic properties of MCM-41 was evaluated in order to develop new catalysts for the trimethylbenzene transalkylation with benzene to produce ethylbenzene, a high-value aromatic in the industry. It was found that chromium decreases the specific surface area but increases the acidity, turning MCM-41 into an active and selective catalyst for ethylbenzene and toluene production. The coke produced on the catalyst is hydrogenated and mainly located outside the pores and thus can be easily removed. The catalyst is more active and selective than mordenite, a commercial catalyst, and thus more promising for commercial applications.

Ethylbenzene dehydrogenation in the presence of steam is the main commercial route to produce styrene. The industrial catalyst is chromium and potassium-doped hematite, which easily deactivates with time due to potassium loss. In order to find non-toxic and potassium free catalysts, the promoter action of zinc on hematite was studied in this work. It was found that zinc acts as structural promoter by stabilizing the Fe3+ species (active phase) as maghemite. Although it decreases the specific surface area, it increases four times the catalytic activity as compared to hematite.