Le bilan d'énergie de surface du Plateau Antarctique est essentiellement contrôlé par les propriétés physiques des premiers centimètres du manteau neigeux. Or l'évolution de cette neige de surface est complexe car elle dépend de processus fondamentalement imbriqués: vitesse de métamorphisme, profils de température, pénétration du rayonnement solaire, précipitations, transport de neige par le vent, etc. L'objectif de ces travaux de thèse est d'étudier ces diverses composantes et leur couplage afin de simuler l'évolution de la densité de la neige et de la taille de grain (surface spécifique) sur le Plateau Antarctique. Pour représenter de manière physique l'absorption de l'énergie solaire à l'intérieur du manteau, un modèle de transfert radiatif à fine résolution spectrale (TARTES) a été implémenté dans le modèle de manteau neigeux détaillé Crocus. TARTES permet de calculer le profil vertical d'absorption d'énergie dans un manteau stratifié dont les caractéristiques sont connues. Parmi elles, la forme des grains, explicitement prise en compte dans TARTES, a été peu étudiée jusqu'à présent. C'est pourquoi une méthode de détermination expérimentale de la forme optique des grains est proposée et appliquée à un grand nombre d'échantillons de neige. Cette méthode, basée sur des mesures optiques, des simulations TARTES, et l'inférence bayésienne, a permis de déterminer la forme la plus adéquate pour simuler les propriétés optiques de la neige, et a mis en évidence le fait que représenter la neige par un ensemble de particules sphériques conduisait à surestimer la profondeur de pénétration du rayonnement d'environ 30%. L'impact de l'absorption en profondeur du rayonnement sur les profils de température dans le manteau et son métamorphisme est ensuite étudié par des approches analytique et numérique, mettant en valeur la sensibilité des profils aux propriétés de la neige proche de la surface. En particulier, la densité de la neige sur les premiers centimètres est cruciale pour le bilan d'énergie du manteau car elle impacte à la fois la profondeur de pénétration du rayonnement et la conductivité thermique du manteau. Puisque le modèle Crocus tient compte de ce couplage entre propriétés optiques et physiques du manteau, il est utilisé pour estimer l'influence des conditions météorologiques sur la variabilité temporelle des propriétés physiques de la neige de surface à Dôme C. Ces simulations sont évaluées au regard d'un jeu de données collectées lors de missions de terrain et de mesures automatiques de l'albédo spectral et de la pénétration du rayonnement dans la neige. Ces observations mettent en évidence le rôle primordial des précipitations dans les variations rapides de taille de grain en surface et l'existence d'un cycle saisonnier de cette taille de grain. Ces variations sont bien simulées par Crocus lorsque le forçage atmosphérique qui lui est imposé est adéquat. En particulier, l'impact du vent sur l'évolution du manteau est fondamental car il contrôle la densité de surface par le biais du transport de neige. Ce transport est aussi à l'origine de la variabilité spatiale des propriétés de la neige observée à Dôme C. C'est pourquoi une modélisation stochastique de l'érosion et du transport de neige dans Crocus est proposée. En plus d'expliquer la variabilité spatiale de la densité et de la taille de grain, elle permet de reproduire celle de l'accumulation annuelle ainsi que les variations rapides de hauteur de neige liées à des épisodes de vent. Ces travaux ont permis une meilleure représentation des processus physiques qui contrôlent les variations des propriétés de la neige de surface à Dôme C, tout en soulignant le rôle primordial du vent, dont l'impact sur le manteau est particulièrement complexe à simuler. / The surface energy balance of the Antarctic Plateau is mainly governed by the physical properties of the snowpack in the topmost centimeters, whose evolution is driven by intricated processes such as: snow metamorphism, temperature profiles variations, solar radiation penetration, precipitation, snow drift, etc. This thesis focuses on the interactions between all these components and aims at simulating the evolution of snow density and snow grain size (specific surface area) on the Antarctic Plateau. To physically model the absorption of solar radiation within the snowpack, a radiative transfer model with high spectral resolution (TARTES) is implemented in the detailed snowpack model Crocus. TARTES calculates the vertical profile of absorbed radiation in a layered snowpack whose characteristics are given. These characteristics include snow grain shape, a parameter that has been seldom studied. For this reason, an experimental method to estimate the optical grain shape is proposed and applied to a large number of snow samples. This method, which combines optical measurements, TARTES simulations and Bayesian inference, is used to estimate the optimal shape to be used in snow optical models. In addition, it highlights that representing snow as a collection of spherical particles results in overestimation of the penetration depth of solar radiation. The influence of the penetration of solar radiation on the snow temperature profiles is then investigated with analytical and numerical tools. The results point out the high sensitivity of the temperature profiles to surface snow physical properties. In particular, the density of the topmost centimeters of the snowpack is critical for the energy budget of the snowpack because it impacts both the effective thermal conductivity and the penetration depth of light. To simulate the evolution of snow physical properties at Dome C by taking into account their interdependence with snow optical properties, the model Crocus is used, driven by meteorological data. These simulations are evaluated against a set of data collected during field missions as well as automatic measurements of snow spectral albedo and penetration depth. These observations highlight the influence of weather conditions on the temporal variability of surface snow properties. They show the existence of a slow decrease of snow grain size at the surface during summer. Rapid changes are also observed, essentially due to precipitation. These variations are well simulated by Crocus when forced by an appropriate atmospheric forcing. In particular, the impact of wind on the evolution of the snowpack is crucial because it controls the surface density through snow transport. This transport is also responsible for the spatial variability of snow properties observed at Dome C. That is why a stochastic representation of snow erosion and transport in Crocus is proposed. It explains well the observations of the spatial variability of density and grain size, and reproduces the variability of the annual accumulation as well as rapid changes in snow height resulting from drift events. This study improves our understanding of the physical processes which drive the properties of snow close to the surface on the Antarctic Plateau, and also points out the critical role of wind, the impact of which is very difficult to account for in models yet.

This thesis describes research carried out to investigate techniques for (i) rapidly assessing the reactivity of fly ash; and (ii) evaluating its interaction with air-entraining admixtures (AEAs), both with regard to use in concrete. The materials considered for the project included, 54 fly ashes from 8 UK sources, and an additional three materials from Bangladesh, covering a range of fineness, loss-on-ignition (LOI) and production conditions (run-of-station, carbon removed, air-classified, co-combustion, oxy-fuel technology); Portland Cements (PCs) from five UK sources with various properties (strength classes 32.5 R, 42.5 N and 52.5 N); laboratory grade hydrated and quick limes; and three commercial AEAs and a standard laboratory grade reagent (surfactant). The research examining fly ash reactivity considered activity index tests to BS EN 450 (BSI, 2005c) as the reference and investigated tests covering fly ash properties/providing measures of fly ash behaviour to rapidly assess this. These included (i) fly ash fineness (45 µm sieve residue, or LASER particle size distribution (PSD) parameters), LOI and flow properties; (ii) accelerated curing of PC and lime-based mortars (iii) lime consumption by fly ash when combined with PC in paste or suspension (Frattini) or from a saturated lime solution; (iv) various measures of fly ash chemical composition (based on oxide/mineralogical analysis); and (v) a quicklime slaking test. The test results were validated by strength tests with 100 mm concrete cube. Results of the above indicated good correlations between fly ash fineness, mortar flow/water requirement and (pozzolanic) activity index (standard or accelerated curing). However, fly ash reactivity and fresh properties appeared to be influenced by the properties of the test PC (e.g. chemical composition and fineness) and there is a need to take this into account during assessment. Generally, finer fly ashes gave better flow; however, there is an optimum fineness (d90 ~40 µm) for best performance, and which is similar to the fineness of the test PC. Strong correlations between the accelerated and standard cured PC-based mortar indicate the latter can be used to estimate the former taking account of the fly ash properties. In view of eliminating the effect of PC properties on reactivity, mortar tests with laboratory grade hydrated lime suggested potential for this. However, for better assessment, this approach requires further work to address issues relating to slower rates of strength gain and increased time requirements, although high temperature conditions were used for curing. Measuring Ca(OH)2 consumption from fly ash/PC paste or suspension agreed with the behaviour in mortar, but needs special instruments (e.g. TGA or XRF). A similar approach with saturated lime did not work well, despite several measures being taken to try and improve this. The oxide and mineralogical analysis results of fly ash did not give good correlations with activity index, but improved when a factor combining them with fineness was considered. The test results were validated in concrete and with air-classified fly ashes from single sources which gave clear trend/behaviour. The lime slaking test was found to be ineffective for identifying fly ash reactivity. The reactivity assessment results were validated by carrying out concrete strength tests. In general, more consistent trends were obtained for fly ash from single source as noted with mortar earlier. Methods adopted/developed to assess the interaction of fly ash with AEA included (i) the foam index test; (ii) acid blue 80 (AB80) dye adsorption test (spectroscopic method); and (iii) methylene blue test. High variability in foam index test results between different operators were noted, which reflected differences in the degree of shaking applied and difficulties in identification of the test end point. Adoption of an automatic shaker and determination of suitable test conditions reduced this by more than 50%. Reliable test procedures were also established for the AB80 dye adsorption method. The results obtained from these tests gave very good correlations with fly ash specific surface area and the AEA dose required (both with commercial AEAs and standard reagent) for achieving target air contents in mortar and concrete. The methylene blue dye test also gave good correlations with these parameters, but was less effective for low LOI fly ashes. Between laboratory tests were carried out at three UKQAA members and considered, LOI, fineness (45 µm sieve and LASER PSD), and activity index. The results gave good agreement with those obtained at the Concrete Technology Unit for this work and again emphasized the role of fly ash fineness on its reactivity. Overall, fly ash fineness was found to be the best means of rapidly assessing its reactivity. Some of the other methods considered gave promising behaviour but require further refinements. Therefore, it is suggested that in addition to 45 µm sieve residue, other types of fineness measurement (e.g. sub 10 µm quantities, d50 and d90) can be considered suitable alternatives to activity index. Similarly, foam index tests with the automatic shaker or the AB80 test method could both be used as fly ash physical requirement tests, or in production control for air-entrained concrete.

Matérias-primas cerâmicas são tecnologicamente muito importantes, pois são aplicadas desde a indústria de base, como isolamento térmico dos fornos siderúrgicos feito pelas cerâmicas refratárias, por exemplo; até a produção de materiais para a construção civil, componentes eletrônicos, entre outros. Devido a essa ampla aplicação, muitos estudos se desenvolveram com o intuito de conhecer as propriedades desses materiais, bem como suas interações com o processamento. Tais propriedades são determinantes para as aplicações e também para as rotas de produção que podem ser empregadas. A principal técnica de processamento cerâmico para consolidação das peças e ganho de propriedades mecânicas é a sinterização. Este processo sofre grande influência das propriedades físicas das partículas que compõem as matérias-primas. O presente estudo se propõe a investigar e monitorar, através de modificações estruturais controladas, quais as características das partículas que mais afetam esta etapa do processamento. Para tal estudo escolheu-se o sistema Al2O3-SiO2 em proporção estequiométrica (3:2) para obtenção de Mulita. Dentre as matérias-primas componentes do sistema, a sílica (SiO2) é a que mais sofre modificações estruturais em uma faixa de temperatura relativamente baixa; logo, foi selecionada para ter suas propriedades modificadas mediante tratamentos térmicos variados, de 700°C, 900°C e 1100°C. As modificações causadas nas propriedades físicas e seus efeitos foram monitorados. Avaliou-se a influência causada na obtenção de mulita estequiométrica, as alterações nas propriedades mecânicas dos corpos de prova sinterizados em temperaturas diferentes (1100°C, 1300°C e 1500°C) durante 3 horas, e a estabilidade dimensional. A sílica aplicada no estudo foi uma sílica amorfa precipitada, disponível comercialmente. Os resultados mostraram que a sílica teve sua área superficial específica (ASE) variando de cerca de 150 m²/g até valores próximos de 0,5 m²/g. Ficou evidente ainda que a variação da ASE das partículas foi responsável por grandes interferências na sinterização ou densificação das estruturas. Este processo depende da movimentação dos átomos para regiões da superfície onde ocorrerá o contato entre as partículas e sua junção. Com a redução da ASE, a sinterização se torna menos efetiva e a estabilidade dimensional é favorecida. Por outro lado, quando a sinterização das partículas é proeminente, a densificação das estruturas dá origem a componentes com boas propriedades mecânicas, aplicáveis em situações estruturais. Os resultados mostraram ainda que é possível obter estruturas com propriedades mecânicas semelhantes, como resistência à ruptura e módulo elástico, mesmo tendo partido de matérias-primas muito diferentes, permitindo o nivelamento e adequação dessas propriedades às aplicações desejadas. / Ceramic raw-materials are technologically very important, once they are applied since basic industry, such as thermal insulating for steel furnace made by refractory ceramics until the production of materials for construction, electronics compounds and others. Due to its wide hall of applications, many studies were developed for understand these materials\' properties and its interaction with processing. Such properties are application and processing route determinant. The main processing technique for consolidating and gaining of mechanical properties is sintering. This process is highly influenced by particles\' physical properties. This very study is proposed to investigate and monitor, by controlled structure modifications, which particles\' characteristics affects sintering more intensely. For such objective, the system Al2O3-SiO2 on stoichiometric proportion (3:2) for mullite obtaining was chosen. Among system\'s raw-material, silica (SiO2) is easier to be modified by temperature in a relatively low range, so it was selected to have its properties changed by different thermal treatment of 700°C, 900°C and 1100°C. Physical properties\' modifications and its effects were monitored. The influence on stoichiometric mullite obtaining, variations on mechanical properties of 3 hours long sintered samples (1100°C, 1300°C and 1500°C), and dimensional stability were measured. Market-available precipitate amorphous silica was employed. Results showed that thermal treatment of silica was able to vary its specific surface area (SSA) from 150 m2g-1 to values near of 0,5 m2g-1. It was also clear that SSA variation was responsible for interfering on sintering. This process depends on atoms movement to surface regions where will occur contact and particles bonding. With SSA reduction, sintering is less effective and dimensional stability is favored. On the other hand, when particles\' sintering is more effective structure densification will end on components with good mechanical properties, finding uses on structural application. Results also showed that is possible to obtain similar mechanical properties structures even when raw-materials exhibit different characteristics.

Nanoporous carbons have become a material of interest in many applications such as electrochemical double layer capacitors (supercapacitors). Supercapacitors are being studied for their potential in storing electrical energy storage from intermittent sources and in use as power sources that can be charged rapidly. However, a lack of understanding of the charge storage mechanism within a supercapacitor makes it difficult to optimize them. Two components of this challenge are the difficulties in experimentally characterizing the sub-nanoporous structure of carbon electrode materials and the electrical performance of the supercapacitors. This work provides a means to accurately characterize the porous structure of sub-nanoporus carbon materials and identifies the current limitations in characterizing the electrical performance of a supercapacitor cell. Future work may focus on the relationship between the sub-nano porous structure of the carbon electrode and the capacitance of supercapacitors, and on the elucidation of charge storage mechanisms.

Nanoporous carbons have become a material of interest in many applications such as electrochemical double layer capacitors (supercapacitors). Supercapacitors are being studied for their potential in storing electrical energy storage from intermittent sources and in use as power sources that can be charged rapidly. However, a lack of understanding of the charge storage mechanism within a supercapacitor makes it difficult to optimize them. Two components of this challenge are the difficulties in experimentally characterizing the sub-nanoporous structure of carbon electrode materials and the electrical performance of the supercapacitors. This work provides a means to accurately characterize the porous structure of sub-nanoporus carbon materials and identifies the current limitations in characterizing the electrical performance of a supercapacitor cell. Future work may focus on the relationship between the sub-nano porous structure of the carbon electrode and the capacitance of supercapacitors, and on the elucidation of charge storage mechanisms.

L’objet de ce travail de thèse porte sur la synthèse originale en milieu fluide supercritique (FSC) de précurseurs « bulk » de catalyseurs d’hydrodésulfuration (HDS) à haute surface spécifique (SBET), destinés à l’HDS de composés soufrés réfractaires tels que le 4,6 diméthyldibenzothiophène (4,6¬ DMDBT). Ce projet a été réalisé en collaboration entre l'Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB-CNRS) et l'Instituto de Tecnología Química de Valencia (ITQ-CSIC) dans le cadre du réseau européen d’excellence Functional Advanced Materials and Engineering of Hybrids and Ceramics (FAMEnoe). Les études à l’ICMCB se sont portées sur l’optimisation des paramètres de synthèse en milieu FSC de NixCo1-xMoO4 (0 ≤ x ≤ 1) (précurseurs métalliques, solvant, température, pression). Des poudres de précurseurs « bulk » majoritairement composées de la phase hydratée (NiMoO4.0,75H2O) - phase la plus active en HDS - de composition contrôlée et pouvant atteindre près de 200 m2.g-1 ont été obtenues et caractérisées.Les propriétés catalytiques de ces précurseurs « bulk » après sulfuration ont ensuite été testées à l’ITQ sur la réaction de Deep-HDS d’un mélange modèle et d’une fraction pétrolière réelle. L’étude souligne plus particulièrement leurs meilleures capacités d’hydrogénation et de catalyse de l’HDS du 4,6 DMDBT que le catalyseur commercial utilisé comme référence dans ces travaux. / This work deals with an original synthesis using supercritical fluids (SCF) of “bulk” catalyst precursors of hydrodesulfurization (HDS) with high specific surface area (SBET) and dedicated to the HDS of refractive sulfur compounds such as 4,6 dimethyldibenzothiophene (4,6-DMDBT). This work was performed in collaboration between the Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB-CNRS) and the Instituto de Tecnología Química de Valencia (ITQ-CSIC) within the Functional Advanced Materials and Engineering of Hybrids and Ceramics network of excellence (FAMEnoe).Studies performed at the ICMCB consisted in optimizing the parameters of the synthesis in SCF of NixCo1-xMoO4 (0 ≤ x ≤ 1) (metallic precursors, solvent, temperature, pressure). Powders of “bulk” precursors mainly consisting of the hydrated phase (NiMoO4.0,75H2O) - the most active phase in HDS - with controlled composition and SBET up to 200 m2.g-1 were obtained and characterized.The catalytic properties of those “bulk” precursors after sulfidation were then tested at the ITQ for the reaction of Deep-HDS of a model feedstock and a real feedstock. The experiments highlighted their better hydrogenation capacity and efficiency in catalyzing the HDS of 4,6 DMDBT than the commercial catalyst used as a reference in this work.

Cette thèse s’inscrit dans l’une des thématiques du «Laboratoire MCEMA», ayant pour projet l’étude physico-chimique des eaux de rivière et l’évaluation de l’influence des activités humaines sur la qualité de l’eau de la rivière LITANI. Ce travail est divisé en trois grandes parties. La 1ère partie a consisté d’étudier les paramètres physico-chimiques (T°, pH, EC, TSS, TDS, ion, etc.) au niveau de l’eau. La 2ème partie s’est concentrée autour de l’analyse des sédiments. Nous avons étudié les sédiments de la rivière de Litani, leurs natures, leurs granulométries, leurs propriétés physico-chimiques (charge et surface spécifique), leurs compositions ainsi que leurs contaminations métalliques. Alors que la troisième a été consacrée à l’étude de l’adsorption de certains polluants présents dans l'eau sur du charbon actif afin d’anticiper sur une étude d’avenir servant à traiter les eaux de cette rivière. Les résultats obtenus entrent dans un projet plus général visant l’étude de méthodes développées pour le traitement des eaux / This thesis is part of one of the focus of research at “MCEMA Laboratory” that concerns the physicochemical study of river water and the evaluation of the possible influence of human activities on the water quality of the Litani River. This work is divided into three principal parts. In the first one, we studied the physicochemical parameters (T, pH, EC, TSS, TDS, ions, etc.) of the water. The second part focuses on the sediment analysis. We studied the sediments of Litani River, their nature, size, composition, physicochemical properties (charge and specific surface area) with the metallic contamination. The third par is devoted the adsorption study of certain pollutants present in water on activated coal in order to anticipate on a future study on the treatment of the water river. The obtained results fall within a broader project on the study of developed methods on the treatment of wastewater

Made available in DSpace on 2016-06-02T19:55:24Z (GMT). No. of bitstreams: 1 2075.pdf: 4577723 bytes, checksum: 80abdc876165c000f61328875ff2a061 (MD5) Previous issue date: 2008-10-20 / Financiadora de Estudos e Projetos / Mixed oxides with perovskite structure have high potential as catalysts in gas depollution processes and particularly in the abatement of nitrogen oxides (NOx). Such solids could be considered as a promising alternative for the replacement of noble metals based catalysts, whose use is predominant. Great flexibility of composition, easy synthesis, low cost and high thermal stability justify the special interest in these materials. However, the low specific surface areas (<10 m2/g) of these solids, when prepared by conventional methods, limit your use in catalytic processes. Some efforts have been made in order to overcome that disadvantage. Nevertheless, the preparation of high surface area ternary or multinary oxides is not easy once their synthesis is associated with solid state reactions carried out at high temperatures. Considering the discussed context, perovskites were obtained in this work by means of a conventional method or via sequencial nanocasting. In the first case, perovskites with LaFe1-xCoxO3 (x = 0, 0.2, 0.3, 0.4, 0.5 and 1) nominal compositions were prepared using the citrate method and nitrate salts as inorganic precursors. In the second case, LaFeO3 and LaFe0.6Co0.4O3 perovskites were obtained by nanocasting using Fluka 05120 activated carbon, Black Pearls 2000 black carbon (Cabot Corporation), and porous carbons nanocasted in Aerosil 200 pyrogenic silica and sílica-SBA-15 mesoporous molecular sieve. X-ray diffraction (XRD), N2 sorption measurements, X-ray fluorescence (XRF), hydrogen temperature programmed reduction (H2-TPR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry (TG) were used to characterize the studied solids. The catalytic activity of the prepared perovskites was evaluated in the reduction of NO to N2 with CO and in the oxidation of the latter compound to CO2. According to the obtained results, it was evident that in comparison with the conventional route, the nanocasting technique using carbons as hard template was efficient to obtain the pure perovskite phase with specific surface areas substantially higher (25 a 49 m2/g). The prepared perovskites were highly active and selective in the reduction of NO to N2 with CO, as well as in the oxidation of the latter compound to CO2. The most active samples were those whose B sites contain up to about 30 % Co. However, the activity of these catalysts decreases strongly with the presence of O2 or water steam. The La-Fe nanocasted binary perovskites showed, in the studied reactions, remarkable higher catalytic activity than the perovskite with the same composition prepared using the conventional method. The higher activity of these materials was related with the increase of their specific surface area. The nanocasted ternary perovskites with LaFe0.6Co0.4O3 composition, despite of the significant increase in their specific surface area, did not show a considerable increase in their activity. This result is in agreement with the behaviour of La-Fe-Co ternary perovskites, in which Co occupies a proportion of B sites greater than 30 %. / Óxidos mistos com estrutura perovskita apresentam alto potencial como catalisadores em processos de despoluição de gases e particularmente no abatimento de óxidos de nitrogênio (NOx). Tais sólidos são uma alternativa promissora para substituição de catalisadores à base de metais nobres, cujo uso é predominante. Vantagens como grande flexibilidade de composição, fácil síntese, baixo custo e elevada estabilidade térmica justificam o especial interesse por esses materiais. Contudo, as baixas áreas superficiais específicas desses sólidos (< 10 m2/g), quando sintetizados por métodos convencionais, limitam o seu uso em processos catalíticos. Algumas tentativas têm sido feitas no sentido de contornar essa desvantagem. No entanto, a obtenção de óxidos ternários ou multinários de alta área superficial específica é especialmente difícil, uma vez que sua síntese está associada a reações no estado sólido realizadas em temperaturas elevadas. Considerando o contexto discutido, neste trabalho foram obtidas perovskitas através de método convencional ou via nanomoldagem seqüencial. No primeiro caso, perovskitas com composição nominal LaFe1-xCoxO3 (x = 0; 0,2; 0,3; 0,4; 0,5 e 1) foram preparadas utilizando o método do citrato e sais de nitratos como precursores inorgânicos. No segundo caso, perovskitas LaFeO3 e LaFe0,6Co0,4O3 foram obtidas por nanomoldagem utilizando carbono ativado Fluka 05120, negro de fumo Black Pearls 2000 (Cabot Corporation), e carbonos porosos nanomoldados em sílica pirogênica Aerosil 200 e peneira molecular mesoporosa sílica-SBA-15. Difração de raios X (DRX), medidas de adsorção/dessorção de N2, fluorescência de raios X (FRX), redução com hidrogênio a temperatura programada (RTP-H2), microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET), espectroscopia no infravermelho por transformada de Fourier (IV) e termogravimetria (TG) foram utilizadas para caracterizar os sólidos estudados. A atividade catalítica das perovskitas preparadas foi avaliada na redução de NO a N2 com CO e na oxidação desse último composto a CO2. De acordo com os resultados obtidos, ficou evidente que em comparação com a rota convencional, a técnica de nanomoldagem utilizando moldes de carbono foi eficiente na obtenção da fase perovskita pura com área superficial específica substancialmente maior (25 a 49 m2/g). As perovskitas preparadas foram altamente ativas e seletivas na redução de NO a N2 com CO, bem como na oxidação desse último composto a CO2, sendo mais ativas aquelas cujos sítios B contêm até cerca de 30 % de Co. A presença de O2 ou vapor de água, entretanto, reduz fortemente a atividade desses catalisadores. As perovskitas binárias La-Fe nanomoldadas apresentaram, nas reações estudadas, atividade catalítica consideravelmente superior a da perovskita com a mesma composição preparada pelo método convencional. A maior atividade desses materiais foi relacionada com o aumento da sua área superficial específica. As perovskitas nanomoldadas ternárias com composição LaFe0,6Co0,4O3, apesar do significativo aumento na sua área superficial específica, não apresentaram um aumento considerável na atividade, fato esse condizente com o comportamento de perovskitas ternárias La-Fe-Co, nas quais o Co ocupa uma proporção de sítios B superior a 30 %.

<p>Electrospinning has gained immense interests in recent years due to its potential application in various fields, including energy storage application. The V₂O₅/GO as a layered crystal structure has been demonstrated to fabricate nanofibers with diameters within a range of ~300nm through electrospinning technique. The porous, hollow, and interconnected nanostructures were produced by electrospinning formed by polymers such as Polyvinylpyrrolidone (PVP) and Polyvinyl alcohol (PVA), separately, as solvent polymers with electrospinning technique. </p> <p> </p> <p>In this study, we investigated the synthesis of a graphene-modified nanostructured V₂O₅ through modified sol-gel method and electrospinning of V₂O₅/GO hybrid. Electrochemical characterization was performed by utilizing Arbin Battery cycler, Field Emission Scanning Electron Microscopy (FESEM), X-ray powder diffraction (XRD), Thermogravimetric analysis (TGA), Mercury Porosimetery, and BET surface area measurement. </p> <p> </p> <p>As compared to the other conventional fabrication methods, our optimized sol-gel method, followed by the electrospinning of the cathode material achieved a high initial capacity of <b>342 mAh/g</b> at a high current density of 0.5C (171 mA/g) and the capacity retention of ~80% after 20 cycles. Also, the prepared sol-gel method outperforms the pure V₂O₅cathode material, by obtaining the capacity almost two times higher.</p> <p>The results of this study showed that post-synthesis treatment of cathode material plays a prominent role in electrochemical performance of the nanostructured vanadium oxides. By controlling the annealing and drying steps, and time, a small amount of pyrolysis carbon can be retained, which improves the conductivity of the V₂O₅ nanorods. Also, controlled post-synthesis helped us to prevent aggregation of electro-spun twisted nanostructured fibers which deteriorates the lithium diffusion process during charge/discharge of batteries.</p>

Self-activation is a process that takes advantage of the gases emitted from the pyrolysis process of biomass to activate the converted carbon. The pyrolytic gases from the biomass contain CO2 and H2O, which can be used as activating agents. As two common methods, both of physical activation using CO2 and chemical activation using ZnCl2 introduce additional gas (CO2) or chemical (ZnCl2), in which the CO2 emission from the activation process or the zinc compound removal by acid from the follow-up process will cause environmental concerns. In comparison with these conventional activation processes, the self-activation process could avoid the cost of activating agents and is more environmentally friendly, since the exhaust gases (CO and H2) can be used as fuel or feedstock for the further synthesis in methanol production. In this research, many types of biomass were successfully converted into activated carbon through the self-activation process. An activation model was developed to describe the changes of specific surface area and pore volume during the activation. The relationships between the activating temperature, dwelling time, yield, specific surface area, and specific pore volume were detailed investigated. The highest specific surface area and pore volume of the biomass-derived activated carbon through the self-activation process were up to 2738 m2 g-1 and 2.209 cm3 g-1, respectively. Moreover, the applications of the activated carbons from the self-activation process have been studied, including lithium-ion battery (LIB) manufacturing, water cleaning, oil absorption, and electromagnetic interference (EMI) shielding.