La réactivité d'un oxyde de manganèse naturel vis-à-vis de quatre composés pharmaceutiques a été étudiée. Alors que la carbamazépine ne présente aucune interaction avec l'oxyde, le paracétamol est éliminé pour des temps de séjour en colonne de quelques minutes et converti en benzoquinone (BZQ) pour pH < 6. La vitesse d'oxydation diminue quand le pH augmente. Le tampon MOPS inhibe la réactivité par des phénomènes de compétition. Le manganèse dissous n'a pas d'influence mais les matières organiques inhibent la formation de BZQ probablement par des réactions de couplage croisées. Le diclofénac est éliminé dans les mêmes conditions avec des effets similaires du pH et du MOPS. L'identification des sous-produits a mis en évidence une décarboxylation du diclofénac. Une analyse par ATR-FTIR a montré l'adsorption du triclosan mais pas d'oxydation. Des capacités d'adsorption ont été obtenues en réacteur fermé et en colonne. Les oxydes de manganèse peuvent ainsi participer à la dégradation de ces molécules dans l'environnement et le traitement de l'eau. / The reactivity of a natural manganese oxide towards four pharmaceutical compounds was studied. Whereas carbamazepine does not interact with the oxide, paracetamol is eliminated for residence time of a few minutes during column experiment and converted into benzoquinone (BZQ) for pH < 6. The oxidation rate decreases with increasing pH. MOPS buffer inhibits the reactivity because of competition mechanism. Dissolved manganese has no effect but organic matter reduces BZQ formation probably through cross coupling reactions. Diclofenac is eliminated in the same conditions with similar effect of pH and MOPS. Identification of by-products shows decarboxylation of diclofenac. ATR-FTIR analysis shows adsorption of triclosan without oxidation. Sorption capacities were obtained in column and closed reactors. Manganese oxides can then participate to the degradation of these molecules in the environment and water treatment.

Philosophiae Doctor - PhD / Supercapacitors are charge-storage devices. Compared to batteries, they have higher power density, more excellent reversibility and longer cycle life. Therefore, supercapacitors have played an increasingly important role in the fields of power source especially in automotive applications, such as electric and hybrid electric vehicles. The higher power density of supercapacitors offers improved vehicle acceleration and the ability to recover more energy from regenerative breaking, since they can be charged and discharged at high current. Generally, the key for supercapacitors to achieve high specific power depends on the inherent properties and the surface areas of their electrode materials. Therefore, current research in the field of supercapacitors has been carried out with increased emphasis on the development of new electrode materials. Optimal novel synthesis of electrode materials for supercapacitor application in hybrid vehicles was accomplished with polypyrrole nanowires, manganese oxide and its carbon composites, ruthenium oxide and its carbon composites being the products. A set of structural and chemical parameters influencing the performance of synthesized electrode materials were identified. Parameters included crystallinity, particle size, particle size distribution, surface area, electrochemical activity. A large range of analytical tools were employed in characterizing the electrode materials of interest. High accuracy and precision in the quantitative and qualitative structural characterization of electrode materials collected by x-ray diffractometry, transmission electron microscopy, scanning electron microscopy and Fourier transform infra-red spectroscopy was demonstrated. N₂-physisorption produced surface area and pore size distribution data of high quality. Cyclic voltammetry, charge and discharge cycling, electron impedance spectroscopy were employed in the electrochemical characterization of the synthesized electrode materials and both qualitative and quantitative information obtained. The techniques were able to discriminate between various synthesized electrode materials and identify the highly electroactive materials. Preparation variables could be critically evaluated for the synthesis of electrode materials. The techniques were deemed to be applicable in discriminating high and low activity electrode materials based on their structural and chemical properties.

Electrochemical supercapacitors (ECs) attract significant attentions for their unique characteristics of high power density, good cycling capability and low cost. This dissertation will focus on fabrication of composite materials for electrodes and devices of ECs. A conceptually new colloidal approach to the fabrication of metal oxide – multiwalled carbon nanotube (MWCNT) composites is proposed. The heterocoagulation of positively charged oxide nanoparticles and negatively charged MWCNT allows the fabrication of advanced nanocomposites with improved dispersion of individual components. The proof-of-principle was demonstrated by the fabrication of MnO2-MWCNT electrodes for ECs with excellent performance. We proposed another novel concept based on electrostatic heterocoagulation of MnO2-MWCNT composites in aqueous environment. In this case, Benzyldimethylhexadecylammonium chloride (BAC) surfactant and caffeic acid (CA) were selected for adsorption and dispersion of MWCNT and MnO2, respectively, and this allowed the formation of stable aqueous suspensions of positively charged MWCNT and negatively charged MnO2. The asymmetric device showed high capacitance, high powerenergy characteristics with enlarged voltage window of 1.8 V, good capacitance retention at high charge-discharge rates and cyclic stability. A novel capacitive material BiMn2O5 was firstly discovered and synthesized for ECs applications in our studies. The BiMn2O5 nanocrystals were prepared by a hydrothermal method. We demonstrated for the first time that BiMn2O5 – MWCNT composite can be used as a new active material for positive electrodes of ECs. The composite electrode with high mass loading showed a capacitance of 6.0 F cm-2 (540 F cm-3) at a scan rate of 2 mV s-1 and excellent capacitive behavior at high scan rates. As-fabricated device showed good cyclic stability in a voltage window of 1.8 V with energy density of 13.0 Wh L-1 (9.0 Wh kg-1) and power density of 3.6 kW L-1 (2.5 kW kg-1). We firstly discovered that Poly[1-[4-(3-carboxy-4 hydroxyphenylazo)benzenesulfonamido]- 1,2-ethanediyl, sodium salt] (PAZO) can be used as an universal dispersant for various materials and its thin film fabricated by electrophoretic deposition (EPD) exhibited photo-induced birefringence. Our new findings indicated that PAZO is good candidate for diverse materials dispersing because it contains diaromatic monomers with salicylate ligands, which can provide multiple adsorption sites for efficient adsorption on particles and impart electrical charges to the particles. Additionally, the use of PAZO polymer offers the advantages of improved steric stabilization. We discovered that Celestine blue (CB) can be developed as an efficient dispersing agent for the nanoparticles. We found that CB includes a catechol ligand, which can provide CB adsorption on inorganic nanoparticles. The relatively large size of the CB molecules is beneficial for the electrosteric dispersion. The benefits of cathodic EPD for nanotechnology were demonstrated by the formation of nanostructured MnO2 films on commercial high surface area current collectors for energy storage in ECs. / Thesis / Doctor of Philosophy (PhD)

In the area of sustainable energy, a major focus has been to design robust electrocatalysts that can be used for the electrolysis of water to produce H2 with a sustainable energy source such as solar. Sustainable H2 generation would potentially be a prelude to the adoption of a hydrogen economy, allowing the phasing out of fossil fuels as a primary fuel source. Toward this end, there is a global research effort to develop electrocatalysts that would facilitate the kinetics of the two half-reactions that make up the water-splitting process: the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). A challenge is to develop active electrocatalysts that are largely composed of earth-abundant elements and show catalytic stability during water splitting at low pH, where the scientific community feels that commercial electrolysis will operate most efficiently. Currently, iridium oxide (IrO2) is being looked at for low pH water splitting because of its stability at low pH, but its relative scarcity (e.g., it is a precious metal) may well make it an unacceptable choice in the long run.In this dissertation, we focus on understanding the scientific issues that will allow the development of earth-abundant catalysts that contain a loading of Ir that is low as possible, while maintaining suitable activity and stability. We began by synthesizing a series of Ir-based OER electrocatalysts by incorporating varying amounts of Ir into 2D layered MnO2 (birnessite, nominally δ-MnO2) and 3D MnO2 (pyrolusite, β-MnO2) phases. The Ir-incorporated δ-MnO2 (Ir/δ-MnO2) electrocatalysts with 16-22 wt% Ir were synthesized by a wet chemical method using a ligating agent, such that Ir was present on the surface and partially intercalated into the interlayer of δ-MnO2. Ir-incorporated β-MnO2 (Ir/β-MnO2) was prepared for the first time via a thermally induced phase transition of Ir/δ-MnO2. This phase transition of δ-MnO2 to β-MnO2 was facilitated by the presence of Ir in the structure, as both Ir in IrO2 and Mn in β-MnO2 could adopt the more thermodynamically stable rutile structure. Extended X-ray absorption fine structure (EXAFS) of Ir/β-MnO2 showed that the catalyst consisted of Ir substituted into the crystalline β-MnO2 lattice, additionally, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscopy (SEM) imaging revealed micron-sized particles with non-uniform distribution of Ir in the MnO2. In 0.5 M H2SO4 electrolyte, 22 wt% Ir/β-MnO2 (60 〖μg〗_Ir cm_geo^(-2)) resulted in the most active catalyst with an η@10 (overpotential at 10 mA cm_geo^(-2)) of 337 mV and stability of 6 h. This electrocatalyst outperformed a commercial IrO2 on a per Ir mass basis. EXAFS, HAADF-STEM and X-ray absorption near edge structure (XANES) showed that 22 wt% Ir/β-MnO2 had a strained structure containing ~41% Mn3+, an OER active species, along with a modified Ir bonding due to the presence of Ir-O-Ir and Ir-O-Mn. Density functional theory (DFT) computation has demonstrated that this modified bonding environment in Ir/β-MnO2 has contributed to enhancing the thermodynamic stability of the structure. Furthermore, the literature suggests that the presence of Ir-O-Mn bond can favorably tune the d-orbital energy of Ir, enabling superior performance in the Ir/β-MnO2 compared to IrO2. The thesis research also included the investigation of the activity and stability of Ir/β-MnO2 that was synthesized via a novel strategy. The resulting material maintained a homogeneous distribution of Ir in the MnO2 lattice and exhibited excellent OER activity and stability. A surfactant-assisted (SA) synthesis method was carried out to achieve uniform doping of 22-28 wt.% Ir in 3D MnO2 (ramsdellite, R-MnO2). Upon annealing, Ir/R-MnO2 transformed to Ir/β-MnO2 (SA), composed of nano-sized particles. Electrochemical studies in 0.5 M H2SO4 showed that, Ir/β-MnO2 (SA) with 75.6 〖µg〗_Ir cm_geo^(-2) exhibited an η of 327 mV and exceptional stability (up to 50 h). At similar Ir mass loadings, the Ir/β-MnO2 (SA) outperformed Ir/R-MnO2 (SA) and commercial IrO2. This enhanced activity and stability was attributed to a thermodynamically stable structure composed of uniform distribution of Ir (Ir-O-Mn) in the MnO2 lattice. Overall, the research results presented in this dissertation contributed towards designing a novel class of Ir-MnO2 catalysts, which potentially will point the scientific community in the right direction for designing future noble metal-incorporated earth-abundant metal oxides for electrocatalytic energy conversion reactions. / Chemistry

Mn oxides have high redox potentials and are known to be very reactive, rendering many contaminants susceptible to degradation via oxidation. Although Mn oxides typically occur as mixtures with other metal oxides (e.g., Fe, Al, and Si oxides) and natural organic matter (NOM) in soils and aquatic environments, most studies to date have studied the reactivity of Mn oxides as a single oxide system. This study, for the first time, examined the effect of representative metal oxides (Al2O3, SiO2, TiO2, and Fe oxides) and NOM or NOM-model compounds (Aldrich humic acid (AHA), Leonardite humic acid (LHA), pyromellitic acid (PA) and alginate) on the oxidative reactivity of MnO2, as quantified by the oxidation kinetics of triclosan (a widely used phenolic antibacterial agent) as a probe compound. The study also examined the effect of soluble metal ions released from the oxide surfaces on MnO2 reactivity. In binary oxide mixtures, Al2O3 decreased the reactivity of MnO2 as a result of both heteroaggregation and complexation of soluble Al ions with MnO2. At pH 5, the surface charge of MnO2 is negative while that of Al2O3 is positive resulting in intensive heteroaggregation between the two oxides. Up to 3.15 mM of soluble Al ions were detected in the supernatant of 10 g/L of Al2O3 at pH 5.0 whereas the soluble Al concentration was 0.76 mM in the mixed Al2O3 + MnO2 system at the same pH. The lower amount of soluble Al in the latter system is the result of Al ion adsorption by MnO2. The experiments with the addition of 0.001 to 0.1 mM Al3+ to MnO2 suspension indicated the triclosan oxidation rate constant decreased from 0.24 to 0.03 h-1 due to surface complexation. Fe oxides which are also negatively charged at pH 5 inhibited the reactivity of MnO2 through heteroaggregation. The concentration of soluble Fe(III) ions ( 4 mg-TOC/L or [alginate/PA] &gt; 10 mg/L, a lower extent of heteroaggregation was also observed due to the negatively charged surfaces for all oxides. Similar effects on aggregation and MnO2 reactivity as discussed above were observed for ternary MnO2‒Al2O3‒NOM systems. HAs, particularly at high concentrations (2.0 to 12.5 mg-C/L), alleviated the effect of soluble Al ions on MnO2 reactivity as a result of the formation of soluble Al-HA complexes. Alginate and PA, however, did not form soluble complexes with Al ions so they did not affect the effect of Al ions on MnO2 reactivity. Despite the above observations, the amount of Al ions dissolved in MnO2+Al2O3+NOM mixtures was too low, as a result of NOMs adsorption on the surface to passivate oxide dissolution, to have a major impact on MnO2 reactivity. In conclusion, this study provided, for the first time, a systematical understanding of the redox activity of MnO2 in complex model systems. With this new knowledge, the gap between single oxide systems and complex environmental systems is much narrower so that it is possible to have a more accurate prediction of the fate of contaminants in the environment. / Civil Engineering

This thesis describes the preparation and characterization of manganese oxide catalysts and their application in the oxidation of acetone, a typical volatile organic compound (VOC), and ozone decomposition. This topic is of great value because of environmental concerns of the elimination of the harmful VOCs and ozone. Manganese oxide was chosen because it is a well-known complete oxidation catalyst for VOCs and also an active catalyst for ozone decomposition. Two cases of studies were carried out in this work. The first study involved the oxidation of acetone using ozone on silica- and alumina-supported manganese oxide catalysts deposited on aluminum oxide foam substrates. The characteristics of the catalysts were determined through various techniques, including x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), Brunauer-Emmett-Teller (BET) surface area analysis, temperature-programmed reduction (TPR), and oxygen chemisorption. The use of these techniques allowed better understanding of the nature of the catalysts. Activity tests were carried out in the acetone oxidation reaction and it was found that the usage of ozone substantially reduced the oxidation temperature. Steady-state in situ Raman spectroscopy was also carried out to better understand the mechanism of the acetone oxidation reaction using ozone. The second study involved an investigation of structural and electronic properties of manganese centers of the MnOx/SiO2 and MnOx/Al2O3 catalysts during the ozone decomposition reaction using in situ x-ray absorption spectroscopy (XAS). The number of surface active sites was again determined through TPR and oxygen chemisorption measurements. The performance of the catalysts with different loadings and supports were also compared. / Master of Science

Yes / The present study explored a novel oxidative desulfurization (ODS) method of light gas oil fuel, which combines a catalytic oxidation step of the dibenzothiophene compound directly in the presence of molecular air as oxidant to obtain high quality fuel for light gas oil. In chemical industries and industrial research, catalysis play a significant role. Heightened concerns for cleaner air together with stricter environmental legislations on sulphur content in addition to fulfill economic have created a driving force for the improvement of more efficient technologies and motivating an intensive research on new oxidative catalysts. As the lower quality fuel becomes more abundant, additional challenges arise such as more severe operation conditions leading to higher corrosion of the refinery installations, catalyst deactivation and poisoning. Therefore, among the technologies to face these challenges is to develop catalysts that can be applied economically under moderate conditions. The objective of this work is to design a suitable synthetic catalyst for oxidative desulfurization (ODS) of light gas oil (LGO) containing model sulphur compound (dibenzothiophene (DBT)) using air as oxidant and operating under different but moderate operating conditions. The impregnation method is used to characterize two homemade catalysts, cobalt oxide (Co3O4/γ-Al2O3) and manganese oxide (MnO2/γ-Al2O3). The prepared catalysts showed that the manganese oxide has a good impregnation (MnO2=13%), good pore size distribution and larger surface area. A set of experiments related to ODS of dibenzothiophene has been carried out in a continuous flow isothermal trickle bed reactor using light gas oil as a feedstock utilizing both catalysts prepared in-house. At constant pressure of 2 bar and with different initial concentration of sulphur within dibenzothiophene, the temperature of the process was varied from 403K to 473K and the liquid hourly space velocity from(LHSV) was varied from 1 to 3 hr-1. The results showed that an increase in reaction temperature and decreasing in LHSV, higher conversion was obtained. Although both catalysts showed excellent catalytic performance on the removal of molecule sulphur compound from light gas oil, the catalyst MnO2 catalyst exhibited higher conversion than Co3O4 catalyst at the same process operating conditions.

High dielectric constant materials are of technological importance as they lead to the miniaturization of the electronic devices. For instance, in the case of memory devices based on capacitive components, such as static and dynamic random access memories, the dielectric constant will ultimately decide the level of miniaturization. In this context, the observation of anomalously high dielectric constant (>10) in the double perovskite Sr2SbMnO6 (SSM) over wide frequency (100 Hz1 MHz) and (190373 K) temperature range has attracted a great deal of attention. However, unfortunately their dielectric losses were also high which limit their use for possible capacitor and related applications. The dielectric loss however was known to decrease with decreasing crystallite size in electroceramics. Therefore, the present work has been focused on the synthesis of nanocrystalline SSM powders by moltensalt route. The characterization of the ceramics fabricated from these powders for their microstructural and dielectric properties. A cubic phase of SSM powder was obtained by calcining the as synthesized powders at 900°C/10h by using sulphate flux. The crystallite size was ~ 60 nm. The activation energy associated with the particle growth was found to be 95 ± 5 kJmol-1 . The ceramic sintered at 1075°C/16h exhibited high dielectric constant (>10at 1 kHz) with low loss (0.72 at 1 kHz) at room temperature. The results are interpreted in terms of a twolayer model with conducting grains partitioned from each other by poorly conducting grain boundaries. Using this model, we attributed the two electrical responses in impedance and modulus formalisms to the grain and grain boundary effects, respectively, while the detected Debyelike relaxation and large dielectric constant were explained in terms of MaxwellWagner relaxation.

Metalorganic Chemical Vapour Deposition (MOCVD) is a versatile technique for the deposition of thin films of oxide materials as it offers advantages, such as deposition over large surface area, conformal coverage, selective area deposition, and a high degree of compositional control. The MOCVD process uses metalorganic (MO) complexes, such as β-diketonate and alkoxide-based complexes, as precursors. These complexes are stable and moderately volatile. Because of the direct bond between metal and oxygen, MO complexes are natural precursors for oxide coatings. As the process involves chemical reactions taking place on the substrate surface, growth of thin films by MOCVD depends on various parameters such as the chemical nature and concentration of precursors, reaction pressure, reaction temperature, and the nature of the substrate. Such a large parameter space of the CVD process, when combined with the dynamics (thermodynamics and fluid dynamics) and kinetics, makes it rather complex. This complexity allows one to make thin films of metastable phases, including amorphous materials. One of the important findings of the work is that MOCVD process is capable of making composite coatings of carbonaceous metal oxide. Manganese is multivalent and forms various stable oxides, such as MnO, Mn2O3, Mn3O4 and MnO2. There are various potential applications of manganese oxides. MnO2 is a very well studied material for its electrochemical applications in dry cells, lithium-ion batteries, and in supercapacitors. Hence, it becomes pertinent to explore the properties of thin films of manganese oxides prepared by MOCVD for various electrochemical and other applications. The thesis work is divided into two parts. Part 1 describes the synthesis of manganese complexes, their characterization, and their application to the CVD of coatings, especially those of carbonaceous MnO. Part 2 is devoted to a detailed study of electrochemical aspects of the carbonaceous MnO coatings, followed by a report on their unusual transport properties. Chapter 1 begins with a brief introduction to thin film deposition processes. In particular, the CVD process is described with reference to various parameters such as carrier gas flow, pressure, temperature and most importantly, the CVD precursor. The chapter ends with a description of the scope of the work undertaken for the present thesis. Chapter 2 deals with “Synthesis and Characterization of MO complexes”. It begins with a description of the classification of CVD precursors with the description of MO complexes such as β-diketonates, which are generally subliming crystalline solids. Manganese β-diketonate complexes are discussed in detail. Due to the multivalent nature of Mn, there are two possible complexes namely Mn(acac)2(H2O)2 and Mn(acac)3. These complexes have been synthesised and characterized (confirmed) by various techniques, such as elemental analysis (CHN), X-ray diffraction (XRD), FTIR spectroscopy, and mass spectroscopy. Thermal analysis of the complexes shows that they are suitable as MOCVD precursors. We have used Mn(acac)2(H2O)2 as a precursor in the present work. Metalorganic complexes, where metal ion is directly bonded with both nitrogen and oxygen, can be potential candidates for the precursor for oxynitrides coatings. We have therefore studied solid crystalline anthranilate complexes of various metal ions, such as Mn2+, Co2+, Cu2+ and Zn2+ and confirmed their formation. Thermal analysis shows that anthranilate complexes are fairly volatile below 250oC and decompose below 500oC. These complexes were pyrolysed in open air and in sealed tube at different temperatures, and the resulting powder product examined by XRD, SEM, EDAX and FTIR. This preliminary study shows that anthranilate complexes yield different oxides of Mn, Co and Cu under different pyrolysis conditions, with very interesting morphological features. Pyrolysis of Zn(aa)2 in a sealed tube leads to the formation of a nanocomposite of carbon and zinc oxide (wuerzite), rich in carbon, with potential for applications in catalysis. On the other hand, the pyrolysis of Zn(aa)2 in air at the same temperature leads to leads to crystalline, nanostructured zinc oxide (wuerzite). However, no attempt has been made to use these anthranilates as CVD precursors. Chapter 3 deals with “MOCVD of Manganese Oxides and their Characterization”. It begins with a brief review of various manganese oxides and their properties. This is followed by description of the CVD reactor used for the present work, together with the conditions employed for the deposition of MnOx films. Depositions have been carried out on different substrates such as SS-316, ceramic alumina and Si (111), while varying various deposition parameters, viz., substrate, reactor pressure, carrier gas (argon) flow rate, and the duration of deposition. Significantly, depositions are divided into two categories: one, carried out in argon ambient, in the absence of a supply of oxygen (or any other oxidant) and the second one, under oxygen flow, using argon as carrier gas. The films deposited in the absence of oxygen flow are thick, black in colour, and electrically conducting, indicating the presence of carbon. The growth rate follows a typical thermal pattern, with activation energy of ~ 1.7 eV. Detailed characterization by XRD, TEM/ED, Raman, FTIR and XPS (X-ray photoelectron spectroscopy) shows that these films are composed of MnO in a carbon-rich amorphous matrix. High-resolution SEM (fig. 1) reveals a fractal pattern of cauliflower morphology, comprising very fine particles (4 – 10 nm), characteristic of very large specific surface area of the film, which is confirmed by volumetric BET measurement (~2000 m2/g). We conclude that growth in argon ambient leads to a homogenous nanocomposite film of hydrated MnO in carbon-rich matrix. Thus, our study reveals that MOCVD is a novel one-step chemical method to produce homogenous composite thin films, wherein all components of the nanocomposite film emerge from the same chemical precursor. Carbon incorporation is generally avoided by empirical process design, as it is viewed as an impurity. The potential advantages of carbon incorporation are thus not examined and the composite nature of carbonaceous films not recognized in the literature. Carbonaceous nanocomposite film can be significant as an electrode in supercapacitors, as discussed in part 2 of the thesis. Chapter 3 describes films deposited under oxygen flow, which are no longer black and are highly resistive, indicating the absence of carbon in the film, as confirmed by Raman spectroscopy. XRD, FTIR and Raman spectroscopy reveal that the films obtained under oxygen flow are more crystalline than the ones obtained in the absence of oxygen flow, and that the films are generally nanocrystalline composites of two manganese oxides, such as MnO and Mn3O4. Given the context of the carbonaceous MnO films described above, chapter 4 begins with a review of electrochemical capacitors (also called supercapacitors or ultracapacitors), which are emerging as important energy storage devices. Until now, in the Mn-O system, hydrated MnO2 has been well-studied as an electrode material due to its low cost and environmental compatibility, but the low electrical conductivity of MnO2, together with irreversible redox reactions, reduces its performance. In electrochemical capacitor applications, metal-oxide/carbon composites are finding importance. Chapter 4 deals with “MnO/C Nanocomposite Coatings as Electrodes for Electrochemical Capacitor”. In this chapter, we have examined the novel EM, i.e., the hydrated MnO/C nanocomposite coating prepared by the MOCVD process on a conducting substrate (current collector) such as SS-316 as an electrode. Electrochemical measurements have been carried out for both the 3-electrode assembly (for basic aqueous electrolyte) and 2-electrode assembly (for gel polymer electrolyte) using cyclic voltammetry (CV), AC impedance and charge-discharge techniques. The studies lead to a maximum specific capacitance of 230 – 270 F/g at 1 mA/cm2 discharge current density for the MnO/C nanocomposite coating grown at 680oC. The Bode plot shows a maximum phase angle of around 74 – 82o, indicating capacitive behaviour. The MnO/C nanocomposite film shows a very small time constant (0.5 – 3 msec), which is good for high frequency applications. The pulse power figure of merit is found to be 650 – 2000 W/g. Capacitance determined for a large number of charge-discharge cycles (~20000), and at large current densities (50 mA/cm2) show promising results. The energy density (5 - 32 Wh/kg) and power density (2 – 4 kW/kg) estimated from charge-discharge data at 1 mA/cm2 shows the potential of the nanocomposite MnO/C as electrode for superior capacitor devices. Gel polymer electrolytes (GPE) offer the advantage of large electrochemical potential window due to its structural and chemical stability. Studies have been carried out to show that the MnO/C nanocomposite film is compatible with gel polymer electrolytes based on poly(methyl methacrylate) (PMMA) and poly(acrylonitrile) (PAN) with salts of magnesium triflate and magnesium perchlorate, respectively) and plasticizers (ethylene carbonate (EC) + propylene carbonate (PC)), in a 2-electrode assembly. Chapter 5 deals with “Magnetoconductance in MnO/C Nanocomposite Coatings on Alumina”. Amorphous systems, such as MnO/C composites wherein carbon is amorphous and MnO is nearly so, are highly symmetric condensed phases, which do not possess long range translational or orientational order. Disorder in the system creates Anderson localized states just above the valence band, which lead to reduced electrical conductivity. Amorphous systems show either a small negative magnetoresistance (~ 5%) or a small positive magnetoconductance (~ 7%) at very low temperatures (~ 10 K). As such, the transport properties of the MnO/C nanocomposite film have been investigated, and are reported in chapter 5. Transport and magnetotransport measurements have been made on the MnO/C nanocomposite film grown on alumina. It is found that the MnO/C nanocomposite coating exhibits a giant negative MR (22.3%) at a temperature as high as 100 K, which is unusual because pure MnO is anti-ferromagnetic and does not ordinarily show any magnetoresistance (MR), while amorphous carbon is known to show a small MR at very low temperatures (~7 K), due to weak-localization. The present results mean that a mechanism other than weak-localization plays a role in this nanocomposite material. Further study of this material is called for, which can perhaps lead to giant magnetoresistance (GMR) at room temperature in a metal-oxide/carbon nanocomposite. A summary of the work and an outlook for further research are given in the concluding chapter 6.

Dans la première partie de mon travail, j'ai préparé quatre catalyseurs différents à base d'oxydes de manganèse: une perovskite (LaMnO3), par voie sol-gel; un oxide simple (Mn2O3), par méthode rapide et un tamis moléculaire octahedrique (OMS-2) par deux méthodes de préparation différentes, via l'état solide (OMS) et la méthode hydrothermale (OMSh). Les propriétés physicochimiques de ces catalyseurs ont été caractérisées par diffraction des rayons X (DRX), adsorption-désorption de N2, analyses thermogravimétriques (ATD/ATG), analyses chimiques (ICP-OES) et réduction en température programmée (H2-RTP). Leurs performances catalytiques ont été évaluées dans la réaction d’oxydation du toluène. Trois cycles catalytiques consécutifs ont été réalisés pour chaque catalyseur afin de confirmer les performances. Afin d'évaluer la stabilité des catalyseurs dans des conditions réactionnelles, les performances catalytiques ont été étudiées sur des expériences de longue durée à température constante, pendant 24 h à 25% de conversion du toluène. Des tests d'oxydation du toluène sur un catalyseur de référence, type Pd/Al2O3 contenant 0,78% en poids de Pd, ont également été effectués à des fins de comparaison. Les caractéristiques cristallines détectées dans les modèles DRX sont bien compatibles avec la formation des structures désirées. Sur la base de leur surface spécifique et de leur réductibilité à basse température, les catalyseurs ont été classés comme suit : OMSs > Mn2O3 > OMS > LaMnO3. Cette tendance est en bon accord avec les performances observées dans l'élimination catalytique du toluène. Un modèle cinétique a été proposé et un bon accord a été obtenu lors de l'ajustement avec les données expérimentales. Dans la seconde partie de mon travail, des catalyseurs LaMnO3 (LM) avec un rapport molaire acide citrique (CA) sur nitrates métalliques (Mn et La) allant de 0,5 à 2 (LM 0,5 à LM 2) ont été synthétisés par méthode sol-gel citrate, afin d'étudier l'effet du rapport de l'acide citrique sur les propriétés physico-chimiques et les performances catalytiques. Les propriétés physicochimiques de ces catalyseurs ont été caractérisées par diffraction des rayons X (DRX), adsorption-désorption de N2 et par spectroscopie d'émission atomique de plasma à couplage inductif (ICP-AES). Sur des échantillons sélectionnés, des caractérisations supplémentaires par analyse thermogravimétrique et thermique différentielle (ATD/ATG), une réduction programmée en température par de l'hydrogène (H2-TPR) et une spectroscopie de photoélectrons X (XPS) ont été réalisées. Les résultats montrent que le rapport molaire acide citrique sur nitrates métalliques influence significativement le profil obtenu en ATD/ATG des solides non calcinés ainsi que les propriétés physico-chimiques des catalyseurs. Les caractéristiques cristallines détectées par DRX sont bien compatibles avec la formation de la phase perovskite LaMnO3. De petites caractéristiques de Mn2O3 ont été détectées dans les diagrammes de diffraction de tous les catalyseurs LM, à l'exception du rapport molaire élevé des nitrates CA / (Mn + La) (1,9 et 2,0). Inversement, des pics La2O3 sont observés pour des valeurs allant de 1,6 à 2, l'intensité la plus élevée étant détectée au rapport molaire égal à 2. Les performances catalytiques ont été évaluées dans l'oxydation du toluène en réalisant trois cycles catalytiques consécutifs pour atteindre des performances stables. Afin d'évaluer la stabilité des catalyseurs dans des conditions de réaction, des expériences à température constante ont été effectuées pendant 24 h à 17% de conversion du toluène. Les catalyseurs LM1.2, LM1.3 et LM1.5 ont montré les meilleures performances catalytiques en oxydation totale du toluène, tandis que LM1 et LM1.7 présentaient un comportement intermédiaire et LM0.8 était peu actif / In the first part of my work, I have prepared four different catalysts based on manganese oxides: a perovskite (LaMnO3), via sol-gel method; a simple oxide (Mn2O3), by rapid method and an Octahedral Molecular Sieve (OMS-2) by two different preparation methods, via solid state (OMSs) and hydrothermal method (OMSh). The physicochemical properties of these catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, TGA/DTA, ICP-OES and H2-TPR. Their catalytic performances were evaluated in the oxidation of toluene. Three consecutive catalytic cycles were performed for each catalyst in order to reach steady state performances. In order to assess the stability of the catalysts under reaction conditions, the catalytic performances were studied upon long-term experiments running for 24 h at 25% of toluene conversion. Tests of toluene oxidation over a typical industrial catalyst, such as a commercial Pd/Al2O3 catalyst containing 0.78 wt% Pd, were also performed for comparison purposes. The crystalline features detected in the XRD patterns are well consistent with the formation of the desired structures. Based on their specific surface area and their low-temperature reducibility, the catalysts were ranked as follows: OMSs> Mn2O3> OMSh> LaMnO3. This trend was in good agreement with the performances observed in the catalytic removal of toluene. A kinetic model was proposed and a good agreement was obtained upon fitting with the experimental data. In the second part of my work, LaMnO3 (LM) catalysts with molar ratio of citric acid (CA) to metal nitrates (Mn and La) ranging from 0.5 to 2 (LM 0.5 to LM 2) were synthesized by citrate sol–gel method, in order to study effect of citric acid ratio on the physico-chemical properties and the catalytic performances. The physicochemical properties of these catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption and by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Over selected samples, additional characterizations by thermogravimetric and differential thermal analysis (TGA/DTA), temperature-programmed reduction by hydrogen (H2-TPR) and X-ray photoelectron spectroscopy (XPS) were carried out. The results show that the molar ratio of citric acid to metal nitrates significantly influenced the TGA/DTA profile of gels along with the physico-chemical properties of the catalysts. The crystalline features detected by XRD are well consistent with the formation of LaMnO3 perovskite phase. Small features of Mn2O3 were detected in the diffraction patterns of all LM catalysts except for high CA/Mn+La nitrates molar ratio (1.9 and 2.0). Conversely, La2O3 peaks appeared for values ranging from 1.6 to 2, the highest intensity being detected at molar ratio equal to 2. The catalytic performances were evaluated in the oxidation of toluene, performing three consecutive catalytic cycles in order to reach steady-state performances. In order to assess the stability of the catalysts under reaction conditions, long-term experiments running for 24 h at 17 % of toluene conversion were carried out. The catalysts LM1.2, LM1.3 and LM1.5 showed the best catalytic performances in terms of toluene conversion, LM0.8 was poor performing, while LM1 and LM1.7 exhibited an intermediate behaviour