<p>Ispitivani su dvostruki slojeviti hidroksidi, LDH i me&scaron;oviti oksidi nastali njihovom<br />razgradnjom, sa različitim sadržajem Mg-Al-Fe i pro&scaron;irenom supstitucijom aluminijuma.<br />Koprecipitacione metode male i velike prezasićenosti odabrane su za sintezu LDH op&scaron;te<br />formule [Mg1_-xM(III)_x(OH)₂](CO₃)_x/2 &sdot; mH₂O, gde M(III) pretstavlja Al i/ili Fe, a x udeo<br />trovalentnih anjona, x = M(III) / [M(II) + M(III)], variran u intervalu 0,15 &lt; x &lt; 0,7.<br />Katalizatori na bazi me&scaron;ovitih oksida sa gvožđem pogodni za upotrebu u redoks<br />reakcijama, formirani su nakon termičke aktivacije - razlaganja LDH. Izvr&scaron;ena je<br />karakterizacija me&scaron;ovitih oksida nastalih iz LDH, kao i netretiranih LDH, ispitivanjem<br />kristalne strukture (XRD), termičke stabilnosti (TG-DTA), teksture (adsorpcija N₂), redoks<br />(H₂ TPR) i kiselo-baznih karakteristika (NH₃ TPD), a utvrđena je i priroda prisutnih vrsta<br />gvožđa (Moessbauer spektroskopija). Pokazano je kako metoda pripreme i obim<br />supstitucije M(III) jona utiču na strukturne, povr&scaron;inske i redoks karakteristike LDH i<br />njihovih me&scaron;ovitih oksida u korelaciji sa katalitičkim svojstvima u odabranim test<br />reakcijama (razgradnja N₂O i redukcija sa NH₃). Utvrđeno je da na katalitičku aktivnost<br />dominantno utiču redoks karakteristike i priroda vrste gvožđa u me&scaron;ovitom oksidu, ali<br />takođe i strukturne karakteristike polaznog LDH, pri čemu je povr&scaron;inska struktura aktivnih<br />centara intervalentnog Fe²⁺-Fe³⁺gvožđa ključna za redoks procese ispitivanih reakcija.<br />Kod svih me&scaron;ovitih oksida dobijenih iz LDH aktivni centri imaju relativno jednake jačine,<br />dok razlike u katalitičkom pona&scaron;anju potiču od razlika u dostupnosti aktivnih centara.<br />Najbolje performanse u katalitičkim reakcijama pokazali su uzorci sa najmanjom<br />stabilno&scaron;ću inicijalnih LDH kod kojih je količina supstituisanih M(III) jona bila blizu<br />granice za inkorporaciju u LDH matricu (x = 0,5), a naročito uzorak sintetisan metodom<br />velike prezasićenosti sa malom količinom dodatne Al(OH)₃ faze.</p> / <p>Layered double hydroxides (LDHs) and derived mixed oxides with different Mg-Al-Fe content and extended aluminum substitution were investigated. High and low supersaturation precipitation methods were used for the synthesis of LDHs with general formula [Mg1_-x M(III)_x (OH)₂](CO₃)_x/2 &sdot; mH₂O where M(III) presents Al and/or Fe and x the content of trivalent ions, x = M(III) / [M(II) + M(III)], varied between 0.15 &lt; x &lt; 0.7. Iron-containing mixed oxides, suitable as catalysts for redox reactions, were formed after thermal activation - decomposition of LDH. Both, LDHs and derived mixed oxides were characterized with respect to crystalline structure (XRD), thermal stability (TG-DTA), textural (N₂ adsorption), redox (H₂ TPR) and acid-base properties (NH₃ TPD) as well as the nature of the iron species (Moessbauer spectroscopy). It was demonstrated how preparation method and the extent of M(III) substitution influence the structure, surface and redox properties of LDHs and derived mixed oxides in correlation to catalytic properties in chosen test reactions (N₂O decomposition and reduction with NH3). The catalytic behavior is mainly determined by the redox properties and the nature of the iron species in mixed oxides, but also by the structural properties of initial LDHs. It was confirmed that surface structure of intervalent Fe²⁺-Fe³⁺ iron active sites is crucial for the redox processes in chosen reactions. The strength of active sites is similar for all mixed oxides derived from LDH, but the differences in catalytic behavior arise from the differences in active sites accessibility. The best catalytic results were obtained when the stability of the initial LDH matrix was lowest e.g. when the amount of substituted M(III) was near the limit for the incorporation into LDH matrix (x = 0.5), especially for the sample synthesized with high superasaturation method containing a small amount of additional Al(OH)₃ phase.</p>

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Os óxidos de enxofre (SOx) são um dos maiores poluentes atmosféricos e um dos precursores da chuva ácida. Um levantamento feito na Petrobrás mostrou que cerca de 17% dos SOx emitidos numa refinaria são oriundos do processo de FCC. Com o avanço dos controles ambientais, traduzido numa legislação mais restritiva, a técnica de incorporação de aditivos para remoção de SOx em UFCCs apresenta-se como a alternativa de menor custo frente outras tecnologias de abate das emissões de SOx. No presente trabalho, foram estudados aditivos constituídos por compostos derivados de hidrotalcitas com a substituição parcial do magnésio e do alumínio por cobre e/ou manganês, sendo estes impregnados ou não por dióxido de cério. Estes aditivos foram submetidos a testes de desempenho em uma unidade multi-propósito acoplada a um micro-GC/TCD. Em todos os testes, a corrente gasosa para a etapa de adsorção oxidativa foi de 1700 ppm de SO2 e 1,5% O2 em He e, para a etapa de regeneração, 30% H2/He. No primeiro conjunto de testes, realizou-se uma adsorção a 720C de 10 min e regeneração com um patamar a 530C, seguido de um TPR até 800C. Observou-se que as amostras impregnadas com cério apresentaram o melhor desempenho na remoção de SO2, indicando que o cério pode ter um papel de promotor da oxidação de SO2 a SO3. Os resultados do TPR mostram que as amostras com cério e com manganês parecem apresentar menores temperaturas de redução dos sulfatos, apesar das maiores liberações de H2S serem identificadas nas amostras com cobre. No segundo conjunto de testes, a adsorção foi a 720C durante 35 min e a regeneração a 650C por 5 minutos em um patamar de 5 minutos, seguida de um TPR até 800C. Para os tempos de sulfatação curtos (5 e 10 min), os resultados confirmaram o efeito positivo que a incorporação de CeO2 apresenta sobre a adsorção oxidativa do SO2. Todavia, para tempos de reação maiores (35 min), não se observou uma correlação clara entre a composição química do catalisador e a quantidade total de SOx removida. Os aditivos foram ainda testados em ciclos de reação-regeneração em condições equivalentes ao segundo conjunto de testes descrito. De um modo geral, os aditivos que contêm cobre têm uma vida útil superior aos demais, possivelmente, pelo fato do cobre ter importante papel na regeneração do aditivo / The sulfur dioxide emissions are one of the most atmospheric pollutant and precursor of acid rain. A survey carried out by Petrobras shows that around 17% of the SOx emissions of its refineries derive from the FCC process. In recent years, the strengthening of environmental controls with more restrictive legislation turns the incorporation of additives for SOx removal into a low-cost alternative technique compared with other technologies of SOx abatement. The purpose of this work is to study additives composed by derivated hydrotalcite compounds with partial substitution of magnesium and aluminium for copper and/or manganese, and with or without dioxide cerium impregnation. The performance of these additives has been tested in a multi-proposal unit coupled with a micro-GC/TCD. In all the tests it was used a gas stream of 1700 ppm of SO2 and 1,5% O2 in He for the oxidative adsorption step and for the regeneration step a 30% H2 in He stream. In the first test, it was carried out an adsoprtion step at 720C for 10 minutes and a regeneration step at a 530C level, flollowed by an TPR until 800C. The cerium dioxide impregnated samples showed a better result for SO2 removal, which implies cerium may play a role as catalyst for SO2 to SO3 oxidation. The TPR results show cerium and manganese may diminish the temperature of sulfates reduction, besides copper samples releases more H2S gases. In the second test, the adsorption step was carry out at 720C for 35 minutes and the regeneration step at 650C for 5 minutes folloewd by a TPR until 800C. In short times reaction (5 or 10 min) the results confirm the positive effect of cerium in the SO2 oxidantion adsorption. However, for longer time reaction (35 min), it cant be observed a relationship between chemical composition of the aditive and the total amount of SOx removed. Additives were still tested in reaction-regeneration cycles in the same conditions of the second test described above. In general, the additives without copper in their composition has a life time minor than that with copper; possibly, because copper plays an important role in the additive regeneration

The reversible and topotactic insertion of guest species within layered host lattices, known as intercalation is a widely studied phenomena. The Layered Double Hydroxides (LDHs) or Anionic Alloys are important class of layered solids with its own distinct ion-exchange host-Guest Chemistry. The LDH structure may be derived from that of Brucite, Mg(OH)2, by random isomorphous substitution of Mg2+ ions by trivalent cations like Al3+, Ga3+ etc. This substitution leaves an excess positive charge on the layers, which is compensated by interlamellar anions. These ions are exchangeable and thus new functionalities can be introduced to ion exchange reactions. Insertion of neutral, non-polar or poorly water-soluble guest molecules remains a challenge. In the present study, two methodologies were adopted to extend the host-guest chemistry of LDHs to neutral and non-polar species, first by using Hydrophobic interaction and second, charge transfer (CT) interaction as driving force. Hlydrophobic interaction as driving force involves functionalization of the Mg-Al-LDH galleries as bilayers, thus covering the essentially hydrophilic interlamellar space of the LDH to one that is hydrophobic and able to solubilize neutral molecules like Anthracene. CT interaction as driving force, involves pre-functionalization of the galleries of the LDH with a donor species e.g. 4-aminobenzoic acid by conventional ion exchange methods to form a LDH-donor intercalated compound. This compound can selectively adsorb acceptor species like Chloranil, Tetracyanoquinodimethane etc. into the interlamellar space of the solid by forming donor-acceptor complexes. The confined donor-acceptor complexes have been characterized by X-Ray Diffraction, UV-Visible, Fourier Transformed Infra-Red and Raman Spectroscopy, Molecular Dynamics Simulations were able to reproduce the experimental results. One dimensional gold nanostructure like nanorods (AuNRs) have received great attention due to their size dependent optical properties, Extending these applications requires assembling the AuNRs into one-, two- and if possible three-dimensional architectures. Several approaches have been developed to assemble AuNRs in two-orientation modes namely end-to-end and side-to-side. The present study self-assembly of the AuNRs has been achieved by anchoring β-cyclodextrin (β-CD) cavities to the nanorods surface. The host-guest chemistry of β-CD has been exploited to assemble the AuNRs. Our strategy was to use a guest molecule that is capable to link β-CD into 1:2 host-guest fashions to link up two β-CD capped nanorods. The guest molecule chosen for the present study was 1,10-phenanthroline. Linkage between the ends of rods leading to V-shaped rods dimmer assembly and side-to-side assembly was achieved by varying the extent of cyclodextrin capping of the AuNRs followed by the addition of linker, 1,10-phenanthroline. The formation of the assembly was characterized using UV-Visible-Near-IR Spectoscopy and Transmission Electron Microscopy.

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Os óxidos de enxofre (SOx) são um dos maiores poluentes atmosféricos e um dos precursores da chuva ácida. Um levantamento feito na Petrobrás mostrou que cerca de 17% dos SOx emitidos numa refinaria são oriundos do processo de FCC. Com o avanço dos controles ambientais, traduzido numa legislação mais restritiva, a técnica de incorporação de aditivos para remoção de SOx em UFCCs apresenta-se como a alternativa de menor custo frente outras tecnologias de abate das emissões de SOx. No presente trabalho, foram estudados aditivos constituídos por compostos derivados de hidrotalcitas com a substituição parcial do magnésio e do alumínio por cobre e/ou manganês, sendo estes impregnados ou não por dióxido de cério. Estes aditivos foram submetidos a testes de desempenho em uma unidade multi-propósito acoplada a um micro-GC/TCD. Em todos os testes, a corrente gasosa para a etapa de adsorção oxidativa foi de 1700 ppm de SO2 e 1,5% O2 em He e, para a etapa de regeneração, 30% H2/He. No primeiro conjunto de testes, realizou-se uma adsorção a 720C de 10 min e regeneração com um patamar a 530C, seguido de um TPR até 800C. Observou-se que as amostras impregnadas com cério apresentaram o melhor desempenho na remoção de SO2, indicando que o cério pode ter um papel de promotor da oxidação de SO2 a SO3. Os resultados do TPR mostram que as amostras com cério e com manganês parecem apresentar menores temperaturas de redução dos sulfatos, apesar das maiores liberações de H2S serem identificadas nas amostras com cobre. No segundo conjunto de testes, a adsorção foi a 720C durante 35 min e a regeneração a 650C por 5 minutos em um patamar de 5 minutos, seguida de um TPR até 800C. Para os tempos de sulfatação curtos (5 e 10 min), os resultados confirmaram o efeito positivo que a incorporação de CeO2 apresenta sobre a adsorção oxidativa do SO2. Todavia, para tempos de reação maiores (35 min), não se observou uma correlação clara entre a composição química do catalisador e a quantidade total de SOx removida. Os aditivos foram ainda testados em ciclos de reação-regeneração em condições equivalentes ao segundo conjunto de testes descrito. De um modo geral, os aditivos que contêm cobre têm uma vida útil superior aos demais, possivelmente, pelo fato do cobre ter importante papel na regeneração do aditivo / The sulfur dioxide emissions are one of the most atmospheric pollutant and precursor of acid rain. A survey carried out by Petrobras shows that around 17% of the SOx emissions of its refineries derive from the FCC process. In recent years, the strengthening of environmental controls with more restrictive legislation turns the incorporation of additives for SOx removal into a low-cost alternative technique compared with other technologies of SOx abatement. The purpose of this work is to study additives composed by derivated hydrotalcite compounds with partial substitution of magnesium and aluminium for copper and/or manganese, and with or without dioxide cerium impregnation. The performance of these additives has been tested in a multi-proposal unit coupled with a micro-GC/TCD. In all the tests it was used a gas stream of 1700 ppm of SO2 and 1,5% O2 in He for the oxidative adsorption step and for the regeneration step a 30% H2 in He stream. In the first test, it was carried out an adsoprtion step at 720C for 10 minutes and a regeneration step at a 530C level, flollowed by an TPR until 800C. The cerium dioxide impregnated samples showed a better result for SO2 removal, which implies cerium may play a role as catalyst for SO2 to SO3 oxidation. The TPR results show cerium and manganese may diminish the temperature of sulfates reduction, besides copper samples releases more H2S gases. In the second test, the adsorption step was carry out at 720C for 35 minutes and the regeneration step at 650C for 5 minutes folloewd by a TPR until 800C. In short times reaction (5 or 10 min) the results confirm the positive effect of cerium in the SO2 oxidantion adsorption. However, for longer time reaction (35 min), it cant be observed a relationship between chemical composition of the aditive and the total amount of SOx removed. Additives were still tested in reaction-regeneration cycles in the same conditions of the second test described above. In general, the additives without copper in their composition has a life time minor than that with copper; possibly, because copper plays an important role in the additive regeneration

Recently, Zn-XAl-YMg coatings have emerged as lighter-weight substitutes for traditional Zn-based coatings for the corrosion protection of steels; however, little is currently known concerning the interactions between the oxides present on advanced high strength steel (AHSS) surfaces and the Zn-Al-Mg bath. In the current contri- bution, the selective oxidation and reactive wetting of a series of C-Mn AHSS were determined with the objective of providing a quantitative description of this pro- cess. The process atmosphere pO2 was varied using dew points of −50◦C, −30◦C and −5◦C. The surface oxide chemistry and morphology were analysed by means of SEM and XPS techniques. Reactive wetting of the selectively oxidized surfaces using a Zn-1.6 wt.% Al-1.6 wt.% Mg bath was monitored as a function of annealing time at 60 s, 100 s and 140 s at 800◦C. The resulting bare spot defects in the Zn-1.6 wt.% Al-1.6 wt.% Mg coating were assessed by means of SAM-AES and FIB, while coating adhesion was analysed by 180◦ bend tests. Annealing the steel substrates resulted in the formation of surface MnO, which varied based on pO2 and Mn alloy content, and that this MnO greatly reduced the wettability of the steel by the Zn-1.6 wt.% Al- 1.6 wt.% Mg bath, resulting in bare spot defects. It was determined that the reactive wetting of the steel substrate was dependant on the oxide morphology and oxidation mode, which was a function of both alloying content of Mn in the steel and annealing pO2 process atmosphere (dew point). Finally, it was concluded that the bare spot area percentage on the coated panels was statistically invariant for annealing times of between 60 s and 140 s at 800◦C. / Thesis / Master of Applied Science (MASc) / Metallic coatings are applied to steels that are not naturally corrosion resistant. The aim of this research was to determine how well a coating containing zinc, aluminum and magnesium adhered to high strength automotive steel. It was deter- mined that manganese oxides formed on the steel during heating prior to applying the metallic coating. The manganese oxides prevented good adhesion between the steel and the coating, resulting in bare spot defects in the coating. The bare spot defects are undesirable as they leave the steel exposed and therefore susceptible to corrosion and are unsightly when painted.

Magnesium alloys are being developed as advanced materials for structural applications where reduced weight is a primary motivator. Alloying can enhance the properties of magnesium without significantly affecting its density. Essential to alloy development, inclusive of processing parameters, is knowledge of thermodynamic, kinetic, and mechanical behavior of the alloy and its constituents. Appreciable progress has been made through conventional development processes, but to accelerate development of suitable wrought Mg alloys, an integrated Materials Genomic approach must be taken where thermodynamics and diffusion kinetic parameters form the basis of alloy design, process development, and properties-driven applications. The objective of this research effort is twofold: first, to codify the relationship between diffusion behavior, crystal structure, and mechanical properties; second, to provide fundamental data for the purpose of wrought Mg alloy development. Together, the principal deliverable of this work is an advanced understanding of Mg systems. To that end, the objective is accomplished through an aggregate of studies. The solid-to-solid diffusion bonding technique is used to fabricate combinatorial samples of Mg-Al-Zn ternary and Mg-Al, Mg-Zn, Mg-Y, Mg-Gd, and Mg-Nd binary systems. The combinatorial samples are subjected to structural and compositional characterization via Scanning Electron Microscopy with X-ray Energy Dispersive Spectroscopy, Electron Probe Microanalysis, and analytical Transmission Electron Microscopy. Interdiffusion in binary Mg systems is determined by Sauer-Freise and Boltzmann-Matano methods. Kirkaldy*s extension of the Boltzmann-Matano method, on the basis of Onsager*s formalism, is employed to quantify the main- and cross-interdiffusion coefficients in ternary Mg solid solutions. Impurity diffusion coefficients are determined by way of the Hall method. The intermetallic compounds and solid solutions formed during diffusion bonding of the combinatorial samples are subjected to nanoindentation tests, and the nominal and compositionally dependent mechanical properties are extracted by the Oliver-Pharr method. In addition to bolstering the scantly available experimental data and first-principles computations, this work delivers several original contributions to the state of Mg alloy knowledge. The influence of Zn concentration on Al impurity diffusion in binary Mg(Zn) solid solution is quantified to impact both the pre-exponential factor and activation energy. The main- and cross-interdiffusion coefficients in the ternary Mg solid solution of Mg-Al-Zn are reported wherein the interdiffusion of Zn is shown to strongly influence the interdiffusion of Mg and Al. A critical examination of rare earth element additions to Mg is reported, and a new phase in thermodynamic equilibrium with Mg-solid solution is identified in the Mg-Gd binary system. It is also demonstrated that Mg atoms move faster than Y atoms. For the first time the mechanical properties of intermetallic compounds in several binary Mg systems are quantified in terms of hardness and elastic modulus, and the influence of solute concentration on solid solution strengthening in binary Mg alloys is reported. The most significant and efficient solid solution strengthening is achieved by alloying Mg with Gd. The Mg-Nd and Mg-Gd intermetallic compounds exhibited better room temperature creep resistance than intermetallic compounds of Mg-Al. The correlation between the concentration dependence of mechanical properties and atomic diffusion is deliberated in terms of electronic nature of the atomic structure.