Academic literature on the topic 'Magnetic heterogeneous catalyst'

The development of a catalyst for the conversion of CO2 and epoxides to the corresponding cyclic carbonates is still a very attractive topic. Magnetic nano-catalysts are widely used in various organic reactions due to their magnetic separation and recycling properties. Here, a magnetic nano-catalyst containing a Schiff base unit was designed, synthesized and used as a heterogeneous catalyst to catalyze CO2 and epoxides to form cyclic carbonates without solvents and co-catalysts. The catalyst was characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric (TG), VSM, SEM, TEM and BET. The results show that the magnetic nano-catalyst containing the Schiff base unit has a high activity in the solvent-free cycloaddition reaction of CO2 with epoxide under mild conditions, and is easily separated from the reaction mixture driven by external magnetic force. The recovered catalyst maintains a high performance after five cycles.

With the rapid development of industry and the increasing demand for transportation, traditional sources of energy have been excessively consumed. Biodiesel as an alternative energy source has become a research focus. The most common method for biodiesel production is transesterification, in which lipid and low carbon alcohol are commonly used as raw materials, in the presence of a catalyst. In the process of transesterification, the performance of the catalyst is the key factor of the biodiesel yield. This paper reviews the recent research progress on homogeneous and heterogeneous catalysts in biodiesel production. The advantages and disadvantages of current homogeneous acid catalysts and homogeneous base catalysts are discussed, and heteropolyacid heterogeneous catalysts and biomass-derived base catalysts are described. The applications of the homogeneous and heterogeneous catalyst derivatives ionic liquids/deep eutectic solvents and nanocatalysts/magnetic catalysts in biodiesel production are reviewed. The mechanism and economic cost of current homogeneous acid catalysts and homogeneous base catalysts are also analyzed. The unique advantages of each type of catalyst are compared to better understand the microscopic details behind biodiesel. Finally, some challenges of current biodiesel catalysts are summarized, and future research directions are presented. This review will provide general and in-depth knowledge on the achievements, directions, and research priorities in developing novel homogeneous/heterogeneous catalysts for the green and cost-effective production of biodiesel.

Catalyst-type mixed metal oxides with different compositions and Co/Fe ratios were obtained from layered double hydroxides to be used as heterogeneous catalysts in the production of biodiesel. The effect of the Co/Fe ratio on the precursors of the catalysts was analyzed, considering their thermal, textural and structural properties. The physicochemical properties of the catalysts were determined by thermogravimetric analysis (differential scanning calorimetry and thermogravimetric), X-ray diffraction, Fourier-transform infrared spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy and N2-physisorption. The conversion to biodiesel using the different catalysts obtained was determined by diffuse reflectance infrared Fourier-transform spectroscopy and 1H-Nuclear magnetic resonance spectroscopy, allowing us to correlate the effect of the catalyst composition with the catalytic capacity. The conditions for obtaining biodiesel were optimized by selecting the catalyst and varying the percentage of catalyst, the methanol/oil ratio and the reaction time. The catalysts reached yields of conversion to biodiesel of up to 96% in 20 min of reaction using only 2% catalyst. The catalyst that showed the best catalytic activity contains a mixture of predominant crystalline and amorphous phases of CoFe2O4 and NaxCoO2. The results suggest that cobalt is a determinant in the activity of the catalyst when forming active sites in the crystalline network of mixed oxides for the transesterification of triglycerides, with high conversion capacity and selectivity to biodiesel.

AbstractOne of the essential themes in modern catalysis is that of bridging the gap between its homogeneous and heterogeneous counterparts to combine their individual advantages and overcome shortcomings. One more incentive can now be added to the list, namely the ability of transition metal complexes to provide strong nuclear magnetic resonance (NMR) signal enhancement upon their use in homogeneous hydrogenations of unsaturated compounds with parahydrogen in solution. The addition of both H atoms of a parahydrogen molecule to the same substrate, a prerequisite for such effects, is implemented naturally with metal complexes that operate via the formation of a dihydride intermediate, but not with most heterogeneous catalysts. Despite that, it has been demonstrated in recent years that various types of heterogeneous catalysts are able to perform the required pairwise H2 addition at least to some extent. This has opened a major gateway for developing highly sensitive and informative tools for mechanistic studies of heterogeneous hydrogenations and other processes involving H2. Besides, production of catalyst-free fluids with NMR signals enhanced by 3-4 orders of magnitude is essential for modern applications of magnetic resonance imaging (MRI), including biomedical research and practice. The ongoing efforts to design heterogeneous catalysts which can implement the homogeneous (pairwise) hydrogenation mechanism are reported.

Magnetic heterogeneous Fe3O4/TiO2/CuO catalyst were synthesized using sol-gel method. The molar ratio of Fe3O4/TiO2/CuO were varied from 1:1:0.1 until 1:1:5. The all synthesized catalyst were characterized using X-ray Diffraction (XRD), Energy Dispersive X-ray (EDX), Field Emission Scanning Electron Microscope (FE-SEM), and Vibrating Sample Magnetometer (VSM). The result show that the magnetic heterogeneous Fe3O4/TiO2/CuO catalyst exhibit ferromagnetic behavior under room temperature. The catalytic performance were evaluated on the degradation of methylene blue under UV light and combination of ultrasound and UV-light Irradiation. The combination of ultrasound and UV-light irradiation exhibit batter catalytic performance than ultrasound irradiation only. The Magnetic heterogeneous Fe3O4/TiO2/CuO with molar ratio 1:1:0.1 shows highest catalytic performance. The reusability of catalyst were also observed.

The commercialisation of biodiesel as an alternative energy source is challenged by high production costs. The cost of feedstock, catalyst and separation of the dissolved catalyst (homogeneous catalyst) from the product are the major contributors to the total manufacturing cost of biodiesel. This study investigated the potential of a heterogeneous catalyst produced from mineral processing waste for biodiesel production. Tailings from the concentration of cupriferous minerals served as the starting material for synthesis of the catalyst. The nanomagnetic catalysts were prepared using co-precipitation (CMCO) and sol-gel (CMSG) methods, combined with zero-valent iron nanoparticles (ZVINPs) to form a hydride catalyst (CMSG/ZVINPs). Catalyst properties were assessed using SEM, TEM, BET and EDX. The catalyst activity was enhanced by a large number of basic sites that were afforded by the presence of calcite and magnesite. Good surface areas and particle sizes of 58.9 m2/g and 15.4 nm, and 52.6 m2/g and 16.9 nm were observed for the catalysts that were prepared using the CMSG and CMCO methods, respectively. 173 emu/g mass magnetisation was obtained for CMSG/ZVINPs, which was sufficient for the catalyst to be regenerated and reused for biodiesel production by exploiting the magnetic properties. The maximum yield obtained with this catalyst was 88% and an average of 27% decrease in biodiesel yield was observed after four reaction cycles. The physicochemical properties of the biodiesel produced complied with the ASTM standard specification. The results showed that mineral processing tailings are a viable starting material for catalyst preparation in biodiesel production.

Gold nanoparticles have shown excellent activity for selective oxidation of alcohols; such catalytic systems are highly dependent on the initial activation of the substrates, which must occur on the catalyst surface in heterogeneous catalysts.

Sulfonated-silica-coated cobalt ferrite (CoFe2O4) magnetic nanoparticles (MNPs-SiCoFe-SO3H) are efficient heterogeneous catalysts for the synthesis of 3,4-dihydropyrimidin-2(1H)-one and octahydroquinazoline derivatives in the absence of solvent. The effects of solvent, temperature, and catalyst amount on the reaction are investigated. The easy separation, reusability of the catalyst, simplicity of the procedure, mild reaction conditions, and good yields (68–95%) within short reaction times (15–70 min) are the advantages of this method. The catalyst can be reused up to eight times with not much loss of activity. Scanning electron microscopy images, X-ray diffraction spectra, and elemental analysis of the recycled catalyst show that the catalyst is stable after the reaction.

L'impact environnemental dû à l'utilisation de carburants et de lubrifiants non renouvelables, associé aux préoccupations liées au changement climatique, a accru la demande de sources d'énergie durables. Les produits d'origine biologique, tels que le biodiesel et les biolubrifiants, sont apparus comme des alternatives aux carburants et lubrifiants minéraux en raison de leur disponibilité, de leur caractère renouvelable, de leurs faibles émissions de gaz, de leur non-toxicité et de leur biodégradabilité. Bien que le biodiesel et les biolubrifiants soient généralement produits par la réaction de transestérification avec des catalyseurs homogènes dans des réacteurs conventionnels, deux défis principaux restent à relever. D’abord, l'utilisation de catalyseurs homogènes nécessite de nombreuses et coûteuses étapes de purification. Les catalyseurs hétérogènes qui ont une surface de contact élevée et qui sont réutilisables et faciles à séparer constituent une solution prometteuse pour pallier ces difficultés. Ensuite, la réaction de transestérification est une réaction lente nécessitant un bon transfert de masse entre les deux liquides non miscibles, l’huile et le méthanol. La production de biodiesel dans des réacteurs agités est souvent limitée, en raison d’une surface d’échange réduite entre les phases et des temps de réaction longs. Il en résulte une faible teneur en biodiesel et la formation de produits secondaires indésirables. Des systèmes de mélange qui favorisent un meilleur contact liquide-liquide afin d'intensifier la réaction de transestérification méritent d’être explorés.L'objectif de cette étude est d’examiner comment améliorer la production de biodiesel et de biolubrifiants via deux manières différentes: en développant un nouveau catalyseur hétérogène et en utilisant un système d’agitation vibrant. Tout d'abord, un catalyseur hétérogène appelé « charbon actif magnétique », dérivé de déchets de coquilles d'amandes et modifié par de l'oxyde de calcium (MAC@CaO), a été synthétisé. Ensuite, le potentiel du MAC@CaO comme catalyseur récupérable pour les réactions de transestérification a été exploré, en se concentrant sur la production d'ester méthylique d'acide gras (EMAG) et de triester de triméthylolpropane (TMPTE). Les conditions optimales de réaction ont permis d'obtenir des rendements en EMAG et en TMPTE de 93,2 % et 95,3 %, respectivement. La recyclabilité du catalyseur MAC@CaO a également été évaluée afin de déterminer sa stabilité chimique. Les rendements en FAME et TMPTE sont restés constamment supérieurs à 85% pendant cinq cycles consécutifs, montrant ainsi le potentiel du nouveau catalyseur. Dans la deuxième partie de cette thèse, le système d’agitation vibrant a été caractérisé afin d'évaluer ses capacités de mélange en monophasique et en multiphasique (solide-liquide et liquide-liquide-solide). L'objectif était de mieux comprendre le fonctionnement de ce système en évaluant le temps de mélange, ses performances pour les suspensions liquide-solide et la production d'émulsions de Pickering. Les résultats montrent que le mélange en monophasique et la suspension des solides sont facilités lorsque l'amplitude des vibrations et le diamètre de la plaque du mélangeur augmentent. Les émulsions de Pickering ont une stabilité supérieure à deux mois. Ensuite, les résultats des expériences de synthèse de biodiesel ont montré une tendance similaire. L'augmentation de l'amplitude des vibrations, du diamètre de la plaque et du nombre de trous coniques dans la plaque s'est accompagnée d'une augmentation de la teneur en EMAG. La teneur maximale en FAME atteinte était de 97,8 % après seulement 30 minutes, durée équivalente ou plus courte qu’avec un réacteur agité. Ce résultat s’explique par une bonne circulation du flux et par une rupture efficace des gouttelettes, ce qui améliore de manière significative les processus de transfert de masse impliqués dans la réaction de transestérification des triglycérides en EMAG
The environmental impact caused by the use of non-renewable fuel and lubricant resources, coupled with concerns about climate change, has increased the demand for sustainable energy sources. Biobased products, such as biodiesel and bio-lubricants, have emerged as alternatives to mineral fuels and lubricants due to their availability, renewability, lower gas emissions, non-toxicity and biodegradability. Although biodiesel and bio-lubricants are typically produced through the transesterification reaction with homogeneous catalysts in conventional stirred-tank reactors, there are two primary challenges associated with each of these processes. Firstly, the use of homogeneous catalysts requires numerous and costly purification steps. Heterogeneous basic catalysts that have high surface area and that are reusable and easy to separate are a promising solution to mitigate these challenges. Secondly, the transesterification reaction is a slow mass-transfer limited reaction that involves two immiscible liquids, specifically triglyceride and methanol. For biodiesel production in stirred-tank reactors there are many associated challenges such as inadequate mixing, limited interfacial area between liquids and long process times. This results in low biodiesel content and the formation of undesirable secondary products. Alternate mixing equipment that improves liquid-liquid contacting to intensify and enhance the transesterification may be required.The objective of this study is to explore two different ways to enhance biodiesel and biolubricant production: by developing a new heterogeneous catalyst and by using a vibromixer to enhance mixing. Firstly, a heterogeneous basic catalyst named magnetic activated carbon, derived from almond shell waste and modified by calcium oxide (MAC@CaO), was synthesized. The resulting material underwent comprehensive characterization using various techniques. Subsequently, the potential of the MAC@CaO as a recoverable basic catalyst in transesterification reactions was explored, focusing on the production of fatty acid methyl ester (FAME) and trimethylolpropane triester (TMPTE). Optimal reaction conditions yielded FAME and TMPTE yields of 93.2% and 95.3%, respectively. The recyclability of the MAC@CaO catalyst was also assessed to determine its chemical stability. FAME and TMPTE yields remained consistently above 85% over five consecutive cycles, highlighting the potential of the developed catalyst. In the second part of this thesis, the vibromixer underwent comprehensive testing to evaluate its mixing capabilities for both single-phase and multiphase (solid-liquid and liquid-liquid-solid) mixing operations. The objective of this assessment was to gain a better understanding of the vibromixer device for various mixing processes by quantify mixing time, cloud height, and Pickering emulsion production before applying it to biodiesel production. The results show that single phase mixing and solids suspension improve when increasing the vibration amplitude and mixer plate size. Pickering emulsions characterized with small droplet sizes (approximately 2 microns) have a stability exceeding two months. Subsequently, the results from the biodiesel production experiments using the vibromixer demonstrated a similar trend. With an increase in vibration amplitude, plate size and the number of conical holes in the plate, the FAME content also increased. The maximum FAME content achieved was 97.8% after only 30 minutes; this is equivalent or shorter than for stirred tank reactors. It is expected that the enhanced reaction is due to good flow circulation and excellent breakup of droplets, which consequently increases interfacial area and significantly improves the mass transfer processes involved in the transesterification reaction of triglycerides into FAMEs

O presente trabalho descreve a preparação de catalisadores magnéticos para aplicação nos processos de fotocatálise heterogênea e ozonização catalítica heterogênea, visando a degradação de poluentes emergentes. Primeiramente buscou-se preparar nanopartículas magnéticas para posterior aplicação no preparo de catalisadores magnéticos de TiO2. Diversas variáveis experimentais foram avaliadas na preparação das nanopartículas magnéticas, tais como: temperatura de reação, tempo de agitação, tempo no ultrasom, velocidade de agitação, velocidade de agitação da base, tempo de agitação do estabilizante, concentração da base e do estabilizante. A influência destes parâmetros de preparação no diâmetro hidrodinâmico e distribuição de tamanho das partículas foi avaliada por meio de um planejamento estatístico. Dependendo das condições experimentais, obteve-se materiais com um tamanho médio variando entre 11 e 36 nm e entre 23% e 77% de distribuição de tamanho. Na condição otimizada, obteve-se partículas com um tamanho médio, obtido pela técnica de espalhamento de luz dinâmico, de 18 nm e 21% de distribuição. O nanomaterial magnético foi utilizado para preparar os catalisadores híbridos Fe3O2@TiO2 e Fe3O4@SiO2@TiO2. Os materiais foram caracterizados por difratoemtria de raios-X (XRD), microscopia de varredura (MEV) e transmissão (TEM), espectroscopia no infravermelho (FT-IR), análise térmica (TG e DTA), espectrometria de emissão óptica (ICP-OES), medidas de área superficial (BET) e espalhamento dinâmico de luz (DLS). Os catalisadores magnéticos foram empregados na degradação dos poluentes emergentes paracetamol; 4-metilaminoantipirina (4-MAA); ibuprofeno; 17 β-estradiol; 17 α-etinilestradiol, e do fenol. Nos processos de degradação também variou-se o efeito do pH nas respostas dos sistemas. De maneira geral, o material Fe3O4@TiO2 apresentou atividade catalítica nos processos de degradação fotoquímica e de ozonização, com desempenho similar ou, em alguns casos, superior ao TiO2. Em relação a 4-MAA, obteve-se, em 60 minutos de tratamento, 25% de mineralização para o processo de fotólise e 66% para o processo de fotocatálise empregando Fe3O4@TiO2. Para o processo de ozonização em pH 3, obteve-se, em 180 minutos de tratamento, 40 e 60% de mineralização para o processo não catalítico e o processo catalítico empregando Fe3O4@TiO2, respectivamente. Os resultados utilizando-se TiO2 foram semelhantes à ozonização não catalítica, o que demonstra o efeito positivo do núcleo magnético para a atividade do material. Assim, o material híbrido multifuncional Fe3O4@TiO2 mostrou-se eficiente para a degradação de poluentes emergentes empregando-se os processos de fotocatálise e de ozonização catalítica heterogênea, possibilitando uma adicional praticidade de separação do meio de tratamento.
The present work describes the preparation of magnetic catalysts for application in heterogeneous photocatalysis and heterogeneous catalytic ozonation processes, aiming the degradation of emerging pollutants. Magnetic nanoparticles were prepered as substratum of magnetic TiO2 catalysts. Several experimental variables were evaluated in the preparation of the magnetic nanoparticles, such as temperature, stirring time, sonication time, precipitation reaction stirring speed, base addition rate, dispersion stirring time, base concentration and stabilizer percentage. The influence of these parameters on particle hydrodynamic diameter and size distribution were measured by a statistical design. Depending on the experimental conditions, materials with an average size ranging between 11 nm and 35 nm and distribution between 23% and 77% were obtained. In the optimum preparation conditions, Fe3O4 magnetic particles with a hydrodynamic diameter of 18 nm and 21% distribution were obtained. The magnetic nanomaterial was used to prepare the hybrid catalysts Fe3O4@TiO2 and Fe3O4@SiO2@TiO2. The prepared materials were characterized by X-ray diffraction (XRD), field-emiss ion scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric (TG), differential thermal analysis (DTA), inductively coupled plasma optical emission spectrometry (ICP-OES), BET specific surface area and dynamic light scattering (DLS). The magnetic catalysts were employed in the degradation of the emerging pollutants paracetamol; 4-methylaminoantipyrin (4-MAA); ibuprofen; 17 β-estradiol; 17 α-ethinyl estradiol, and phenol. In the treatment processes the effect pH on the systems was also varied. In general, the material Fe3O4@TiO2 showed catalytic activity in the processes of photochemical degradation and ozonation, with performance similar or, in some cases, superior to TiO2. For example, the 4-MAA mineralization, after 60 minutes of treatment, by the photolysis process reached a m aximum value of 25%. In the same treatment time by the photocatalytic process using Fe3O4@TiO2 it was obtained 66% of 4-MAA mineralization. For the ozonation process, in pH 3, after 180 minutes of treatment, 40% of 4-MAA mineralization was achieved by non-catalytic method. On the other hand, in the same treatment time employing Fe3O4@TiO2, 60% of 4-MAA mineralization was obtained. In addition, for the ozonation process using TiO2 similar results to non-catalytic ozonation were observed, which demonstrates the positive effect of the magnetic core for the activity of the catalyst. Thus, the hybrid material Fe3O4@TiO2 was efficient for the degradation of emerging pollutants employing the photocatalysis and heterogeneous catalytic ozonation processes, allowing an additional practicality for separating the catalyst from the treatment medium.

Surface catalysed reactions play an important role in chemical productions. Developments of catalyst requiring high activity whilst improving on product selectivity can potentially have a profound effect in the chemical industry. Traditional catalyst modifications were focused on tuning the size, shape and foreign metal doping to form well defined metal nanoparticles of unique functionalities. Here, we show new approach to engineering of metal nanocatalysts via a subsurface approach can modify the chemisorption strength of adsorbates on the surface. Carbon modified nanoparticles were synthesised using glucose to stabilise Pd nanoparticles at a molecular level. Upon heat treatment, the carbonised glucose encapsulated the Pd nanoparticles with carbon atoms take residence in the octahedral holes (15 at.%). These materials were tested in liquid phase stereoselective hydrogenations of 3-hexyn-1-ol and 4-octyne. The former has importance in the fragrance industry towards the production of leaf fragrance alcohol. It was shown for the first time that the geometrically and electronically modified Pd with interstitial carbon atoms reduced the adsorption energy of alkenes, ultimately leading to higher reaction selectivity. Boron modified Pd nanoparticles was synthesised using BH₃.THF in the liquid phase. The material possess high B interstitial saturation (20 at.%), which can be synthesised for the first time below 100°C. These materials were tested in the liquid phase selective hydrogenation of various alkynes and 2-chloronitrobenzene, of which the latter has importance in the pesticides industry. Kinetic modelling on the hydrogenation of 4-octyne suggests these subsurface occupied B does play a pivotal role on increasing the reaction selectivity, as removal of these species lead to decreased selectivity. Au nanoparticles were synthesised and characterised using H¹³COOH NMR. The new liquid NMR characterisation method is successfully applied to examine the chemisorption strength of metal nanoparticles. An attempt to synthesise PVP capped B modified Pd nanoparticles with the above NMR characterisation was investigated. It is believed the examples of subsurface atom modifications as shown here may offer future catalyst developments in this area.

Nano-deposits of Ni and Co, supported on porous oxide materials, serve as heterogeneous catalysts within Johnson-Matthey plc. in the steam reforming and Fischer-Tropsch processes, with the size, shape and dispersity of the metal crystallites linked to the catalytic profile. Here we study the magnetic properties of nickel systems synthesised on the nano-scale, with the aim of developing an industrially viable technique by which the diameter of the nickel species can be evaluated. A series of nickel nanoparticles, synthesised via the thermal decomposition of Ni(acac)2, are studied as a model for the catalytic systems. The nanoparticles were studied via magnetometry and microscopy to identify the super-paramagnetic and nuclear volume of the particles, respectively. The magnetisation studies demonstrate that the widely used Langevin function based method of particle sizing does not reflect the total nuclear volume, and a surface correction term is introduced based on the low temperature, high applied field magnetisation. To demonstrate the applicability of the proposed analysis, the study of a series of industrially-viable precipitation catalysts are reported. The catalysts are studied via x-ray diffraction (XRD) and gas adsorption to establish comparable values of crystallite diameter. The values of crystallite diameter determined from the magnetic analysis are demonstrated to be consistent with the range of sizes determined from the XRD and gas adsorption studies, with additional sensitivity to the polydispersity of the crystallites. During the study of the precipitation catalysts, the magnetic volume was demonstrated to be reduced from the nuclear volume. This behaviour was also confirmed via small angle neutron scattering experiments, which demonstrated a magnetic scattering volume reduced from the nuclear by = 1 nm, on the order previously reported for nano-ferromagnetic materials. Through these studies we have established the methods for determining the surface correction term to magnetic granulometry studies. We have demonstrated that the corrected values are in agreement with the nuclear volumes determined via TEM, gas adsorption and XRD and that our proposed technique for the study of catalyst crystallites requires a short time scale, is insensitive to the catalytic support and is sensitive to the distribution of crystallite diameters.

Les réactions pallado-catalysées permettant la formation de liaisons carbone-carbone trouvent de nombreuses applications en synthèse organique et constituent l'étape clé de la synthèse d'un grand nombre de molécules. La première partie de cette thèse décrit la préparation et l'étude de catalyseurs hétérogènes et réutilisables comportant du palladium supporté sur un polymère portant des groupements phosphinés, polymère dérivé soit d'une résine de Merrifield soit d'une résine Rasta. De très bons résultats ont été obtenus pour leur utilisation dans les couplages croisés de Hiyama, Heck et Suzuki et dans chaque cas la possibilité de réutilisation jusqu'à 4 fois du catalyseur a été vérifiée. Notre travail constitue une des premières utilisations d'un catalyseur réutilisable dans le couplage de Hiyama. Nous avons aussi mis au point des conditions permettant d'effectuer le couplage de Heck en présence d'une quantité infime de palladium. Notre étude sur les résines Rasta constitue la première application de ces supports en pallado-catalyse. La deuxième partie de la thèse décrit l'étude de la préparation de catalyseurs où le palladium serait supporté sur des nanoparticules superparamagnétiques et qui pourraient donc être récupérés de tout milieu réactionnel grâce à un champ magnétique externe. Des nanoparticules de cobalt ont été préparées puis recouvertes de pyrocarbone par dépôt chimique en phase vapeur. Des groupements organiques ont été fixés sur la coque de carbone, ce qui permet l'introduction de ligands phosphinés. La structure de ces particules a été étudiée par microscopie électronique en transmission et leur préparation optimisée en fonction des résultats structuraux.

The first experimental work discussed in this thesis is a series of reaction studies to look at the effect of four solvents - methanol, propan-1-ol, propan-2-ol and octanol - on the hydrogenation of 4-tertiary butyl phenol (TBP). Experiments are first done in a stirred pot-type reactor with two different sized catalyst particles and the rate and selectivity were compared. The same reaction was also performed in a small trickle bed reactor so that the effect of the reactor could be considered along with the effect of particle size and solvent. The next three areas of experimental work, use NMR to examine the effect of the four solvents on mass transport issues. Firstly the diffusion of solvents within alumina pellets is investigated using a technique known as pulsed-field gradient (PFG) NMR. A two component model is fitted to the data and is explained on the basis that the larger diffusion coefficient gives the pore (or ordinary) diffusion rate, while the smaller diffusion coefficient gives a rate of diffusion which is reduced due to the effect of interaction with the pore wall. The same technique is then exploited to study the effect of the solvent on diffusion of TBP in liquid mixtures. In particular, the effect of concentration is considered, and models for diffusion at infinite dilution are compared with data extrapolated from experimental data. Strong association is seen between the TBP and the smaller polar solvents which weakens with increasing alcohol solvent size. The effect of temperature on the diffusion of solvents is effectively modelled by an Arrhenius equation. Magnetic Resonance Imaging (MRI) is used to look at the effect of the solvent on the hydrodynamics during trickle flow. 2D cross-sectional images were taken through the trickle bed were taken and algorithms were developed and applied to calculate the hold-up and wetting efficiency for each solvent over at least five different liquid flowrates. The solvents were then ranked based on these characteristics and trends seen between solvents were found mainly to depend on the viscosity of the solvent.

In this manuscript, the application of different nanocatalysts derived from metal oxides impregnated on the surface of the magnetite in different reaction of general interest in Organic Chemistry is described. In the First Chapter, a cobalt derived catalyst was used to study the hydroacylation reaction of azodicarboxylates with aldehydes. In the Second Chapter, a catalyst derived from copper was used to perform different reactions, including homocoupling of terminal alkynes and the subsequent hydration reaction to obtain the corresponding 2,5-disubstituted benzofurans, the reaction of alcohols and amines (or nitroarenes) to obtain the corresponding aromatic imines, the cross-dehydrogenative coupling reaction of N-substituted tetrahydroisoquinolines using deep eutectic solvents and air as final oxidant. Finally, the formation of benzofurans from aldehydes and alkynes through a tandem coupling-allenylation-cyclization process has been performed. In the Third Chapter, a bimetallic catalyst derived from nickel and copper was used to study the multicomponent reaction between benzyl bromides, sodium azide and alkynes to obtain the corresponding triazoles. In the Fourth Chapter, a catalyst derived from palladium was used in the direct arylation of heterocycles using iodonium salts. Also the synthesis of 4-aryl coumarins through the Heck arylation reaction and subsequent cyclization using the same catalyst is described. In the last Chapter, the use of different eutectic mixtures were studied as alternative media to perform in a single vessel the cyclation reaction of N-hydroxy imidoyl chlorides and alkynes, without any type of catalyst under oxidizing conditions.

Operando spectroscopic techniques are inevitable tools for deriving relevant relations between structure and performance of catalysts in a reaction as a basis for rational catalyst design. To ensure that the catalysts under study are indeed analyzed in their active working state, the spectroscopic cells must be connected to some kind of on-line product analysis for providing simultaneously data on conversion, selectivity, as well as spectroscopic data. This chapter provides an overview of the most common methods applicable in true operando mode with flowing reactants, at elevated temperatures and a total pressure of p ≥ 1 bar, including X-ray diffraction (XRD), absorption (XAS) and emission methods (XES), vibrational (FTIR and Raman) and electronic spectroscopy (UV-vis), as well as magnetic resonance techniques (NMR, EPR). For each technique, the basic principles, opportunities and limitations of the method are mentioned first, followed by a presentation of typical experimental setups and some instructive application examples from heterogeneous catalysis. The latter are described in more detail; however, application opportunities in homogeneous catalysis are also mentioned. At the end of this chapter, some ideas on future trends are put forward.

This chapter discusses materials chemistry, focusing on solid-state compounds, their synthesis, structure, and electronic, magnetic, and optical properties. Important applications of these solid materials include optoelectronics, renewable energy generation and storage, and heterogeneous catalysis using porous materials. The chapter describes how inorganic materials are synthesized as bulk solids. It shows the important role of defects in controlling the properties of solids, including ion migration. Then it focuses on key classes of inorganic materials, including intercalation compounds, photovoltaics, and photocatalysts, complex electronic oxides, magnetic compounds, framework structures, and their use as heterogeneous catalysts, pigments, and molecular materials. The discussion in the chapter also touches on nanomaterials chemistry, an area that has developed enormously in the past decade.

Nanostructured metal oxides represent one of the most important and well-recognized classes of materials owing to their unique size-tunable properties (e.g., optical, electronic, magnetic, catalytic, and mechanical), which make these materials potentially suitable for technological applications in the fabrication of devices for energy harvesting and storage, photonics, sensors as well as medical and biological applications. In the last two decades, the use of microwave irradiation, either alone or in conjunction with other synthesis techniques, has grown in popularity among scientists and researchers for the production of nanostructured oxides. In this chapter, we especially provide a detailed insight into microwave-assisted synthesis of different nanostructured materials including pure metal oxides, mixed metal oxides, spinels, perovskites, and composite oxides because these materials have attracted significant research interest.