This thesis includes both experimental and modelling studies on the treatment of drinking water. Three aspects were studied: (i) removal of fluoride (F– ) by adsorption, (ii) removal of fluoride and other contaminants by solar distillation, (iii) denitrification by a microbial fuel cell. The availability of potable water on earth is about 0.2% of the total available water. This very small quantity is polluted by anthropogenic and natural contaminants. Fluoride is a classic example of a natural contaminant, wherein the dissolution of F– bearing minerals causes the release of F– into the groundwater. Exposure to concentrations > 1 mg/L over ex-tended periods of time results in dental and skeletal fluorosis. Worldwide, about 220 million people are at risk. Nitrate is an example of anthropogenic contaminant, occurring because of addition of high quantities of fertilizers to the soil for better crop yields. The excess fertilizers penetrate the soil and mix with the groundwater, resulting in nitrate contamination. The major effect of nitrate contamination is met haemoglobin , which is caused because of the oxidation of ferrous ion in haemoglobin to ferric ion by the nitrite to form haemoglobin. The effects can be noticed by the change in colour of skin to bluish grey or brownish grey in infants. To counter the drastic effects of these anions, the World Health Organization (WHO) has prescribed permissible limits of 1.5 mg/L and 45 mg/L for F– and NO3 – , respectively. For obtaining contaminant-free water, many methods have been used. Reverse osmosis (RO) is one of the widely-used methods. Even though this process removes most of the contaminants, about 50 - 70% of the inlet water is wasted as a reject stream with higher concentrations of the contaminants. This is a very unsustainable way of using water, particularly in drought-prone areas. So, in the thesis a conceptual strategy with three different methods is developed to treat reject water. In the first part of the thesis, the removal of F– using adsorption was studied. Activated alumina (AA) and a hybrid anion exchange resin embedded with hydrous zirconium oxide nanoparticles (HAIX-Zr) (sample sent by Prof. Arup K SenGupta) were used as the adsorbents. The adsorbents were tested with synthetic water samples and reverse osmosis (RO) reject water. HAIX-Zr had a better adsorption capacity compared to AA when water containing only F– was used. The presence of high concentrations of co-ions affects the uptake of F– drastically, with a decrease of up to 34% and 79% for AA and HAIX-Zr, respectively. With AA, for a synthetic water sample with a small concentration of HCO3 – , there was a two-fold increase in the uptake of F– compared to a water sample containing only F– . There was no removal of NO3 – by AA. HAIX-Zr removes NO3 – , but to a lesser extent than F– . With AA, the pH of the inlet solution affected the adsorption capacity, because of the change in the surface charge of AA. Based on the type of water sample used, the cost of treated water varied from Re. 0.1 - 1.0/L ($ 0.0015 - 0.015/L) for AA and 0.2 - 11.5/L ($ 0.003 - 0.17/L) for HAIX-Zr. A community-level plant was set up to treat the RO reject water using AA. Due to challenges at the field level, the pilot plant had to be stopped after 80 bed volumes of water were treated. From our observations and as also reported by many authors, the adsorption of F– is affected by the presence of many ions. When modelling the adsorption of F– , it is usually taken as a single entity getting adsorbed on the adsorbent. As this is not a proper assumption, a model was developed which takes into account all the speciation reactions that take place during adsorption, and all the species like H+, OH– , Na+, Cl– , and NO3 – present in the solution along with F– . Using the model, the equilibrium constants and rate constants for the reactions were obtained. For one initial concentration of F– , a good fit was obtained to the batch adsorption data, except at short times. Due to uncertainty about the amount of impurity present in the adsorbent, at higher initial concentrations of F– , there was a significant discrepancy between predictions and data. Considering column experiments, the breakthrough curve for F– was simulated using the developed model. For the special case of negligible mass transfer resistances, the predicted break-through volume was within 3% of the observed value. In the second part of the thesis, nitrate removal was investigated using microbial fuel cell (MFC). In a MFC, power is generated by the activity of the microorganisms present in the cell. The organisms present in the anode side release electrons (e– ) by the use of substances that can be oxidized, namely, glucose, acetate, etc. On the cathode side, the organisms have the potential to take in e– and reducible substances, and release reduced products like nitrogen, hydrogen, etc. In the present case, nitrates added to the cathode side were reduced to nitrogen gas by the use of a consortium of micro-organisms taken from seawater. A similar consortium was used in the anode chamber Here, the study was focused on improving the efficiency of MFC for removal of NO3 – , by changing the buffering medium used in the cells. Commonly, phosphate buffer is used, but when using a MFC for treatment, the presence of PO43 – causes water contamination and is not suitable for drinking. There-fore, PO43 – was replaced with HCO3 – on the cathode side of the cell. This resulted in a higher removal of NO3 – and power production compared to the PO43 – buffered solution In the third part of the thesis, contaminant removal using solar distillation was investigated. For this as inclined basin still was used. Investigations were based on the evaporation rate of contaminated water, and the odour and concentrations of ions in the distillate. In order to improve the evaporation rates, different radiation absorbing materials like sand, activated charcoal, and carbon nanoparticles encapsulated in polymer sheets (PCNP) were investigated. It was observed that the evaporation rates were higher with activated carbon than the other materials. Using this technique there was about 99% removal of NO3 – , F– , SO42 – and the concentrations of ions in the distillate were well below the acceptable limits. When sand or PCNP was used as an absorbing/wicking medium, the distillate had an objectionable odour. With the use of AC, the odour could be eliminated because of the adsorption of odour-causing compounds.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-07-22T14:59:52Z No. of bitstreams: 1 HeytorVitorSouzaBezerraDeAzevedo_DISSERT.pdf: 4226943 bytes, checksum: 879f905d96e12f6e15faa6de0fec4be5 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-07-26T22:08:45Z (GMT) No. of bitstreams: 1 HeytorVitorSouzaBezerraDeAzevedo_DISSERT.pdf: 4226943 bytes, checksum: 879f905d96e12f6e15faa6de0fec4be5 (MD5) / Made available in DSpace on 2016-07-26T22:08:45Z (GMT). No. of bitstreams: 1 HeytorVitorSouzaBezerraDeAzevedo_DISSERT.pdf: 4226943 bytes, checksum: 879f905d96e12f6e15faa6de0fec4be5 (MD5) Previous issue date: 2016-01-29 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Comp?sitos ? base de alumina (Al2O3), carbeto de tungst?nio (WC) e cobalto (Co) apresentam propriedades espec?ficas como baixa densidade, alta resist?ncia ? oxida??o, alto ponto de fus?o e elevada in?rcia qu?mica. Esse comp?sito revela ser um material promissor para ser aplicado em diversos campos da engenharia. Este trabalho tem como objetivo avaliar algumas propriedades mec?nicas durante a confec??o e, ap?s a sinteriza??o do comp?sito (Al2O3 - WC - Co). P?s comp?sitos com a composi??o de 80%.p de Al2O3, 18%.p de WC e 2%.p de Co foram processados pela rota de moagem de alta energia (MAE), em moinho planet?rio por 50 horas, bem como por mistura manual em um recipiente de vidro, seguindo a mesma propor??o em peso. Amostras foram coletadas (2, 10, 20, 30, 40 e 50 horas) durante o processo de moagem. Em seguida, os p?s foram prensados no formato de amostra circular com di?metro de 5 mm em uma prensa uniaxial com press?es de 200 e 400 MPa. A sinteriza??o ocorreu de duas maneiras: a primeira sinteriza??o via fase s?lida foi realizada ? 1300 ?C e ? 1126 ?C durante 1h com taxa de aquecimento de 10?C/min em forno resistivo sob atmosfera de arg?nio as press?es de compacta??o utilizadas foram de 200 e 400 MPa, a segunda sinteriza??o foi realizada em dilat?metro via fase s?lida ? 1300 ?C com press?o de compacta??o de 200 MPa, tamb?m foi realizada em dilat?metro outra sinteriza??o, desta vez por fase l?quida ? 1550 ?C com press?es de compacta??o de 200 e 400 MPa, obedecendo os mesmos par?metros utilizados no forno resistivo. As mat?rias-primas foram caracterizadas por difra??o de raios X - (DRX), fluoresc?ncia de raios X - (FRX), microscopia eletr?nica de varredura (MEV), espectroscopia por dispers?o de energia (EDS) e particulometria a laser. As amostras sinterizadas foram submetidas a ensaios de microdureza. Os resultados mostraram que a moagem de alta energia atingiu os objetivos quanto ao tamanho de part?cula e a densifica??o do comp?sito. Entretanto, a microdureza n?o alcan?ou resultados significativos, isso ? um ind?cio que o comp?sito possui baixa tenacidade ? fratura. / Composites based on alumina (Al2O3), tungsten carbide (WC) and cobalt (Co) exhibit specific properties such as low density, high oxidation resistance, high melting point and high chemical inertia. That composite shows to be a promising material for application in various fields of engineering. In this work, the mechanical properties of the composite (Al2O3 ? WC ? Co), particularly density and hardness, were evaluated according to the effects of the variables of powder processing parameters, green compact and sintered. Powder composites with the composition of 80 wt% Al2O3, 18 wt% WC and 2 wt% Co were processed by high energy ball milling in a planetary mill for 50 hours as well as mixed by manual mixing in a glass vessel with the same proportion. Samples were collected (2, 10, 20, 30, 40 and 50 hours) during the milling process. Then, the powders were compacted in a cylindrical die with 5 mm in diameter in a uniaxial press with pressures of 200 and 400 MPa. The sintering was in two stages: first, the solid phase sintering was performed at 1126 and 1300 ?C for 1 hour with a heating rate of 10 ?C/min in a resistive furnace under argon atmosphere for green samples compacted in 200 and 400 MPa; the second sintering was performed on dilatometer in solid phase at 1300 ?C for green sample compacted in 200 MPa, another sintering also was performed on dilatometer, this time in liquid phase at 1550 ?C for green samples compacted in 200 and 400 MPa, with the same parameters used in resistive furnace. The raw materials were characterized by X ? ray diffraction (XRD), X ? ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and laser particlemeter. The sintered samples were subjected to microhardness testing. The results showed that high energy milling achieved to the objectives regarding the particle size and the dispersion of composite phases. However, the hardness did not achieve to significant results, this is an indication that the composite has low fracture toughness.

Neste trabalho estudamos a interação de troca entre a camada antiferromagnética (AFM) de IrMn, e a ferromagnética (FM) de Co, no sistema IrMn/Co através de uma camada espaçadora. Usamos dois materiais com propriedades distintas como espaçador, ou o Cr (um material antiferromagnético com anisotropia fraca) ou a alumina (Al2O3, material isolante, não-magnético), para analisarmos o alcance dessa interação. Caracterizamos o sistema através de diferentes técnicas, ou seja, medidas de magnetização estática, ressonância ferromagnética, difratometria e refletividade de raios-X, microscopia de força atômica e microscopia eletrônica de transmissão. Tratamentos térmicos na presença de campo magnético foram feitos a fim de maximizar o efeito de exchange bias. Inicialmente, investigamos como utilizar adequadamente os diversos modelos fenomenológicos na interpretação de dados experimentais. Mostramos, através da utilização de dois modelos e de um simples experimento, a importância de considerarmos a distribuição de eixos fáceis e a anisotropia uniaxial do material FM. Negligenciar essas considerações pode ser a causa, ou pelo menos parte, das grandes diferenças relatadas em trabalhos experimentais referente à avaliação da interação FM/AFM obtida por meio de diferentes técnicas de medida. Também mostramos que, mesmo quando o modelo descreve corretamente uma bicamada que apresenta exchange bias, nenhuma das técnicas convencionais de caracterização, reversíveis ou irreversíveis, aplicadas à mesma amostra, é capaz de distinguir entre os campos de acoplamento de troca e o de anisotropia AFM, se a razão entre estes for suficientemente grande ou pequena. Demonstramos que o valor do acoplamento FM/AFM pode ser determinado a partir da variação da coercividade com a espessura da camada AFM. Dos resultados experimentais (tanto nas medidas de magnetização quanto nas de ressonância ferromagnética) obtidos para as tricamadas IrMn/Al2O3/Co, é ressaltada a variação do campo de exchange bias com o aumento da espessura da camada isolante e nãomagnética de alumina. Foi observado que a intensidade do acoplamento entre Co e IrMn diminui exponencialmente com o aumento da espessura da camada de alumina, sendo esta supressão muito abrupta, com decaimento pelo menos quatro vezes mais rápido que os anteriormente relatados. Estes resultados foram explicados em termos da perda do contato direto entre as camadas AFM e FM com o aumento da espessura da alumina. A série de IrMn/Cr/Co apresentou um comportamento oscilatório das grandezas campo de exchange bias e coercividade em função da espessura da camada de cromo, bastante peculiar. O valor do campo de anisotropia rodável, obtido a partir das simulações de FMR, tem sinal oposto ao do caso clássico, indicando que este campo é antiparalelo ao campo magnético externo aplicado. Ainda observa-se uma tendência geral de aumento do campo de anisotropia rodável com a espessura de Cr sugerindo que, nestas amostras, há uma grande contribuição proveniente da camada de Cr para esse campo. / The present work reports on the exchange interaction between an antiferromagnetic (AFM) layer, i.e., IrMn, and a ferromagnetic (FM) one, Co, in IrMn/Co systems across spacer layers. Two materials with distinct properties were used as spacers, namely Cr (weak anisotropy antiferromagnet) and alumina (Al2O3, a non-magnetic insulator material), in order to investigate the intensity of this coupling. The systems were characterized using several different techniques, i.e., static magnetic characterization, ferromagnetic resonance, X-ray diffractometry and small-angle reflectivity, atomic force microscopy as well as highresolution transmission electron microscopy. Magnetic annealing was used in order to maximize the exchange-bias effect. First, it was investigated how to correctly employ different phenomenological models for experimental data interpretation. It was demonstrated, through two models and a straightforward experiment, that it could be very important to consider the easy-axis distributions and the uniaxial anisotropy of the FM material. Neglecting these distributions or underestimating the FM anisotropy could be the reason, at least in part, for the significant differences in the evaluation of the AFM/FM exchange coupling obtained via different measurement techniques reported in experimental works. It was also shown here that even when the adopted model describes correctly the EB system, none of the conventional reversible or irreversible techniques, applied to the same sample, is capable to distinguish between the exchange coupling and the AFM anisotropy fields if their ratio is sufficiently high or low. It is demonstrated that the values of AFM/FM coupling can be properly determined with the help of the variation in the coercivity with the AFM layer thickness. In the experimental results (obtained here using both static magnetic characterization and ferromagnetic resonance) of the IrMn/Al2O3/Co trilayers, special attention was paid on the EB field variation with the thickness of the non-magnetic insulator alumina spacer. It was observed that the IrMn/Co coupling strength decreases exponentially with the alumina spacer thickness, being the exponential decay length at least four times smaller than the values previously reported for exchange-bias systems. Such a rapid suppression of the coupling is explained in terms of the prompt loss of the direct contact between the antiferromagnet and the ferromagnet with the alumina layer's thickness. The IrMn/Cr/Co series presented an oscillatory behavior of both exchange bias and coercive fields as a function of the Cr layer thickness, which is rather peculiar. The value of the rotatable anisotropy field, estimated from the ferromagnetic resonance measurements, shows a sign oppose to that normally obtained, indicating that this field is antiparallel to the external applied magnetic field. Moreover, the general tendency for enhancement of the rotatable anisotropy field with the Cr spacer thickness suggests that, in these samples, there exists a considerable contribution coming from the Cr layer to this field.

Neste trabalho foram avaliados os efeitos da adição de polímeros precursores na sinterização, microestrutura, dureza e na tenacidade à natura de materiais cerâmicos à base de carbeto de silício e de AI2O3. As matérias-primas cerâmicas foram caracterizadas por análise semi-quantitativa por espectrometria de fluorescência de raios X, difração por laser, adsorção gasosa e microscopia eletrônica de varredura. Para os polímeros utilizou-se análise termogravimétrica. A cinética de sinterização das amostras compactadas foi estudada por dilatometria. A caracterização dos materiais sinterizados incluiu medidas de densidade aparente pelo princípio de Arquimedes e/ou por picnometria de He, porosimetria por intrusão de Hg, análises de difração de raios X, de carbono total, avaliação da microestrutura e por microscopia eletrônica de varredura e de transmissão, análise por espectrometria de raios X por dispersão de energia, ensaios de impressão Vickers para determinação de dureza e tenacidade à fiatura. No estudo de cerâmica à base de carbeto de silício foram utilizados os aditivos óxidos AI2O3 (4% em peso) e Y2O3 (4% em peso) e os aditivos poliméricos PMHS (polimetilhidrogenossiloxano) e polimetilhidrogenossiloxano com D4Vi. O processamento envolveu a cura do material, pirólise e sinterização (1850 °C e 1950 °C/l h. Ar ou N2). Nas amostras à base de carbeto de silício houve elevada perda de massa, principalmente quando a atmosfera de sinterização foi argônio. As amostras à base de carbeto de silício, com adição de polímeros atingiram densidade de até 3,15 g/cm3 quando pirolisadas a 900 °C em N2 e sinterizadas a 1950 °C, em atmosfera de nitrogênio. Para as amostras à base de alumina foram utilizados os aditivos poliméricos PMHS, PMS (polimetilsilsesquioxano) e PPS (polifenihnetilvinilhidrogenosilsesquioxano) e as sinterizações foram realizadas a 1650 °C e 1700 °C, não havendo variações significativas nas densidades obtidas nas duas temperaturas. Nos materiais com adição de PMHS foram obtidos compósitos de alumina e mulita, sendo que os grãos de mulita foram formados intergranularmente. Nas amostras contendo PMS ou PPS a distribuição das feses formadas, Si2Al4O4N4 e Si2ON2, foi bastante heterogênea, A obtenção de compósitos cerâmicos utilizando pequenas adições de polímeros precursores cerâmicos mostrou-se viável para materiais à base de alumina, sendo uma rota simples de conformação, com grande potencial para a obtenção de peças com geometria complexa. / The effects of the addition of precursor polymers on sintering, microstructure, hardness and fiacture toughness of silicon carbide and alimiina ceramics were studied. The ceramic raw materials were characterized by semi-quantitative analysis by X-ray fluorescence, particle size by laser diffraction, specific surface area by gas adsorption and microstructural analysis by scanning elecfron microscopy. The polymers were analyzed by thermogravimetry. The sintering kinetics of cold-pressed specimens was studied by dilatometry. The sintered materials were characterized by evaluation of apparent density by the Archimedes technique and/or helium picnometry, by mercury porosimetry, by X-ray diflftaction, by evaluation of total carbon content, by scanning and transmission electron microscopy, by enetgy dispersion X-ray spectrometry, and by Vickers indentation analysis for determining hardness and fiacture toughness. AI2O3 (4wt.%) and Y2O3 (4wt.%) and polymetylhydrogenosiloxane and polymetylhydrogenossiloxane with D4Vi were the sintering aids for SiC. The processing procedures were material cure, pyrolysis and sintering (1850 X and 1950 °C/1 h, Ar or N2). High mass loss was measured in silicon carbide based ceramics, mainly under argon. Silicon carbide based ceramics with polymer sintering aids achieved 3.15 g/cm3 density after pyrolysis at 900 °C under N2 and sintering at 1950 °C under nitrogen. PMHS, PMS and PPS polymer sintering aids were used for almnina based ceramics sintering carried out at 1650 °C and 1700 °C, without significant difference in the final density. Addition of PMHS yielded alumina and mullite composites, with intergranular mullite grains. Heterogeneous Si2AI4O4N4 and Si2ON2 phases were obtained in specimens with PMS or PPS, The preparation of ceramic composites using small amounts of precursor polymers showed a suitable process for alumina-based ceramics, a simple forming route, with high potential for the fabrication of complex shape pieces.

L'objectif de ce travail de thèse est la compréhension de l'impact des propriétés acido-basiques des supports oxydes sur l'interaction métal-support ainsi que les effets du milieu réactionnel sur les propriétés structurales, électroniques, thermodynamique et réactives des catalyseurs métalliques hyper-dispersés. Le catalyseur modèle choisi est un agrégat monométallique de platine déposé sur alumine qui est la référence des études fondamentales pour permettre des progrès dans la compréhension de ce système complexe. La mise en œuvre de calculs dans le formalisme de la théorie de la fonctionnelle de la densité, réalisés à partir de modèles moléculaires périodiques, a permis de déterminer l'état de surface du catalyseur pour des conditions de température et de pression représentatifs de l'expérience. L'influence de la taille des particules conjointement à la présence de chlore sur la stabilité thermodynamique des agrégats de Pt supportés sur alumine-γ a démontré une stabilisation significative des agrégats Pt3 lors de la migration d'espèces de surface (H, OH et Cl) sur la particule. La reconstruction d'une morphologie biplanaire (la plus stable en absence d'hydrogène) vers une morphologie cuboctaédrique pour les forts taux de recouvrement en hydrogène sur les particules de Pt supportées a été démontrée et permet d'expliquer plusieurs observations expérimentales encore mal comprises. L'impact du milieu réactionnel sur la rupture C-C et C-H à partir de l'éthane sur l'agrégat Pt13 supporté sur alumine- γ a été démontré. Les résultats obtenus permettent de mieux comprendre l'importance des conditions de température et de pression du milieu réactionnel (notamment du rapport P(H2)/P(C2H6)) sur la stabilité des intermédiaires réactionnels. Ces résultats sont en accord avec les observations expérimentales et permettent de mettre en évidence que l'optimum de pression en hydrogène est relativement élevé dans le cas des réactions de reforming catalysées par du Pt seul. / The aim of this work is the understanding of the impact of acido-basic properties of oxide supports on the metal-support interaction as well as on the effects of reactive conditions on the structural, electronic, thermodynamic and reactive properties of hyper-dispersed metallic catalysts. The chosen model catalyst is a monometallic platinum cluster supported on alumina which is the reference of fundamental studies to improve the understanding of this complex system. DFT calculations were performed from periodic models to determine the surface state of the catalyst under representative experimental temperature and pressure. The influence of nano-clusters' size combined with the presence of chlorine on the thermodynamic stability of supported Pt clusters on γ-alumina demonstrated a significant stabilization of Pt3 clusters with the migration of surface species (H, OH and Cl) on the particle. The morphology reconstruction from biplanar (the most stable in absence of hydrogen) to a cuboctahedral morphology for the high hydrogen coverages on the supported Pt13 cluster is demonstrated and explains several experimental observations still controversial. The impact of the reactive conditions on the C-C and C-H bond scission from ethane on the Pt13 cluster supported on γ-alumina was demonstrated. Results helps to better understand the importance of temperature and pressure conditions in the reactive medium (notably the P(H2)/P(C2H6) ratio) on the stability of reactive intermediates. These results are in agreement with experimental observations and highlight that the optimum of hydrogen pressure is relatively high in the case of catalytic reforming reactions catalyzed by Pt only.

Ce travail porte sur le procédé NSR (NOx Storage-Réduction) de dépollution des gaz d'échappement automobile Diesel. Des catalyseurs contenant 2,12% Pt déposés sur alumine, cérine-zircone ou cérine modifiée, ont été caractérisés et évalués dans des conditions NSR, avec un regard particulier sur la sélectivité de la réduction des NOx. Les tests catalytiques sont effectués dans des conditions complexes : cycles 60s de stockage (mélange pauvre)/ 4s de réduction (mélange riche), avec des traces de réducteurs dans la voie pauvre et d’oxydant dans la voie riche. Des sélectivités importantes en N2O (gaz à effet de serre) ont pu être observées. Les émissions de N2O varient en fonction de la nature du support, de la température et des réducteurs mis en œuvre (C3H6, CO, H2 ou mélange C3H6+CO+H2). Dans certaines conditions, la présence de réducteur dans les phases pauvres contribue à la majorité du N2O émis lors des cycles NSR. Ces valeurs sont en bon accord avec les résultats obtenus en parallèle en régime stationnaire (SCR). A 200°C, H2 donne la plus grande sélectivité en N2O, essentiellement à cause de la réduction partielle des NOx en milieu pauvre. En revanche, à 300°C, C3H6 est le réducteur le plus sélectif en N2O, toujours avec une forte contribution des phases pauvres. Les résultats sont plus homogènes avec les catalyseurs supportés sur oxydes redox car ils favorisent la transformation des réducteurs dans la voie riche (réactions du gaz à l’eau et reformage de C3H6), conduisant à mélange réducteur moyenné. Les propriétés redox du support permettent aussi de limiter les émissions de NH3. / Lean reduction of NOx was studied on NSR (NOx storage-reduction) catalyst, with a special attention on N-compound selectivities. Platinum (2.12wt%) catalysts supported on various supports (alumina, ceria-zirconia and modified ceria) were characterized and evaluated in cycling conditions. Catalytic tests were performed and realistic and complex conditions: 60s for the storage phases (lean periods)/ 4s for the reduction (rich pulses). Gas mixture was composed of reducers and oxidants in both lean and rich atmosphere. In these conditions, high N2O emissions were measured (powerful greenhouse gas). The N2O selectivity depends on the redox properties of the support, the temperature and the chemical nature of the reducer (C3H6, CO, H2 or C3H6+CO+H2 mixture). In some conditions, more than half of the N2O production can occur during the storage phase, in lean condition. These results are in good agreement with those obtained in specific SCR tests. At 200°C, H2 lead to the higher N2O selectivity especially due to the partial NOx reduction in the lean period. At 300°C, N2O emission is mainly favoured with C3H6, with still a high contribution of the lean pulses. Results are less distinct with supported catalysts on redox material, due to the support involvement in the reducer transformation reactions (water gas shift and steam reforming), leading to a blend of reducers in the rich pulses. In addition, lower NH3 emissions were observed on platinum supported on redox oxides.

In the Fischer-Tropsch (FT) synthesis, CO and H2 (synthesis gas) are converted into hydrocarbons that can be further upgraded to high-quality fuels and chemicals. Different carbon sources such as natural gas, coal and biomass can be used as feed-stocks for the synthesis gas. In commercial applications, supported cobalt catalysts are commonly used in the FT synthesis, especially when the synthesis gas emanates from natural gas and when the desired final product is diesel. The activity and selectivity of a cobalt catalyst is dependent on several parameters, one of them being the support. The present thesis is focused on the design, synthesis and characterization of alumina and silica materials (with and without Ce and Zr promoters) with non-conventional morphology, and evaluation of their feasibility as cobalt supports in the FT synthesis. Ce- and Zr-alumina nanoparticles were synthesized by co-precipitation in water-in-oil microemulsion. The obtained product is amorphous alumina with highly dispersed promoters, resulting in strong cobalt-support interactions and low cobalt reducibility. By increasing the calcination temperature of the Ce-promoted support, crystalline CeO2 is obtained which apparently increases the cobalt reducibility and thereby the catalytic activity (per gram catalyst). The small pore size of the materials may induce diffusion limitations on the reactants arrival and/or result in very small cobalt particles, which favour methane over long-chain hydrocarbons.  Successful preparations of pore expanded mesoporous silicas with 1D, 2D and 3D pore structures via the atrane route, combined with the addition of swelling agents, have been demonstrated. The advantage of this method is that pore expansion can be achieved at mild conditions and there is no need for a post-synthesis process using an autoclave system. In larger silica support pores, larger cobalt particles will be formed and the weaker the cobalt-support interactions will be. This generally results in a higher cobalt reducibility for larger-pore supports and thereby a higher catalytic activity. / <p>QC 20171004</p>

Le contrôle de la porosité des supports de catalyseurs est un enjeu important dans l'industrie du raffinage. L'objectif de cette thèse est de développer un nouveau procédé de précipitation afin d'obtenir des alumines γ présentant des propriétés texturales originales vis-à-vis de celles préparées de façon conventionnelle par précipitation de boehmite en réacteur agité. Pour cela, les influences combinées du précurseur, de la technologie de mélange et du temps de micromélange sur les propriétés physiques du produit final ont été étudiées. Ce travail de thèse propose donc une comparaison de trois technologies de mélange : un réacteur agité conventionnel, un réacteur à disque tournant et un disperseur rotor-stator. Les gammes de temps de micromélange accessibles avec chacun de ces réacteurs sont déterminées par la méthode iodure-iodate. L'étude porte sur la précipitation de deux précurseurs de l'alumine : la boehmite, classiquement utilisée, ainsi que la NH4-dawsonite, dont l'intérêt pour la préparation de supports de catalyseurs est plus récent. Leur solubilité est estimée dans la mesure du possible à l'aide des données thermodynamiques de la littérature. Dans le cadre de cette étude préliminaire, un modèle de suivi de la sursaturation en fonction du temps de micromélange est mis en place à l'aide des équations cinétiques de la précipitation de la boehmite. La caractérisation de la NH4-dawsonite précipitée en réacteur agité met en évidence l'intérêt de ce précurseur pour obtenir des alumines à forte porosité présentant des diamètres poreux moyens entre 10 et 30 nm. Une nuance est toutefois apportée aux fortes surfaces spécifiques généralement revendiquées sur ce matériau dans la littérature. Malgré tout, les propriétés texturales de l'alumine ex-dawsonite présentent une évolution thermique atypique lui permettant de se démarquer de l'alumine ex-boehmite. L'étude de la précipitation en mélangeur rapide met en évidence une grande différence de comportement entre les deux précurseurs. Contrairement à la boehmite, la forte sensibilité de la NH4-dawsonite au temps de micromélange permet d'obtenir une large gamme de propriétés texturales. Ce travail de thèse confirme donc l'intérêt de la NH4-dawsonite comme précurseur alternatif de l'alumine pour obtenir des propriétés texturales originales. L'utilisation de plusieurs systèmes précurseur / technologie de mélange s'avère également prometteuse pour couvrir une large gamme de propriétés texturales / Control of catalyst supports porosity is an important challenge for the refining industry. The aim of this thesis is to develop a new precipitation process in order to obtain γ-alumina supports exhibiting new textural properties compared with those prepared by the conventional boehmite precipitation route in stirred tank reactor. For that purpose, combined influences of precursor, mixing technology and micromixing time on the final product physical properties were studied.Three mixing technologies were compared: a classic stirred tank reactor, a sliding surface mixing device and a rotor-stator mixer. Micromixing time ranges achievable with each of these reactors were determined using the iodide-iodate method. The study focused on the precipitation of two alumina precursors: boehmite, usually used, and NH4-dawsonite, which interest for catalyst supports preparation is quite recent. A model was developed to simulate the supersaturation evolution as a function of the micromixing time, based on boehmite precipitation kinetic equations.Characterization of NH4-dawsonite precipitated in a stirred tank reactor confirmed this precursor interest in order to prepare high porosity aluminas with mean pore diameters ranging between 10 and 30 nm. Study of the precipitation conducted in fast contacting mixers highlighted a significant difference in the behaviour of both precursors. Contrary to boehmite, NH4-dawsonite high sensitivity to micromixing time led to a wide range of textural properties.This thesis work therefore confirms the NH4-dawsonite potential as an alternative alumina precursor in order to reach new textural properties. The use of several precursor / mixing technology systems has also proven promising to cover a wide range of textural properties

No description available.

Excess fluoride (F-) in drinking water poses a health threat to millions of people around the world. In the present work, activated alumina (AA) has been used as an adsorbent. Data obtained from batch experiments were fitted to the (i) pseudo-first order, (ii) pseudo-second order, and (iii) Langmuir kinetic model. Model (ii) performed better than model (i), and fitted the data well. However, the rate constant for adsorption ka had to be varied as a function of the initial concentration of F- in the liquid phase c0. A more satisfactory approach is provided by Langmuir model, which fitted the data reasonably even though ka was independent of c0. Shreyas (2008) developed a model for the batch adsorption of F- onto porous pellets of AA. Some errors were detected in his computer program were corrected. The parameters of the model were estimated by fitting predictions to data. The parameter values suggest that the adsorption process is likely to be diffusion limited. Column experiments were conducted as follows. The pellets were soaked in deionized water for a time ts before they were loaded into columns. A feed solution having a fluoride concentration cf = 3 mg/L was fed to column and the concentration of F- in the exit stream ce was measured at regular intervals. Breakthrough was deemed to have occurred when ce exceeded the permissible limit (= 1 mg/L). Constant values of the bed height H, and the empty bed contact time tc were used in the experiments. The volume of treated water V, scaled by the volume of the bed Vb, varied strongly with the soaking time ts, with a maximum at ts = 24 h. To understand the possible reasons for this behaviour, XRD, FESEM, and FTIR were used to characterize the surface of AA. Though the concentrations of the surface hydroxyl groups may influence the adsorption of F-, FTIR studies show there is no direct correlation between V/Vb and the concentrations of these groups. The FESEM and XRD studies indicate that fresh AA consists mainly of boehmite, which gradually converted to gibbsite during soaking. For fixed values of H and tc, the dimensionless volume of treated water V/Vb was a maximum at D = 45 mm. This behaviour may be caused by wall effects for small values of D and by occurrence of quasi-static regions near the wall for large values of D. The cost of treated of water was Rs. 0.42/L. It decreased slightly to Rs. 0.37/L after one regeneration cycle, but increased to Rs. 0.41/L after two cycles. The volume of treated water after two regeneration cycles was 595 L/kg. The concentration of Al3+ ions ca in the treated water increased and exceeded the permissible limit of 0.2 mg/L as the number of regeneration cycles increased. The concentration of F- in regeneration effluent cre was in the range 32-70 mg/L. The effluent was subjected to solar distillation, leading to a distillate whose fluoride concentration F- was in the range 9-12 mg/L. The distillate can be discharged into the public sewers, as the permissible limit is 15 mg/L.