Dissertations / Theses on the topic 'Monolithic Catalyst'

L'objectif de ce travail est la synthèse et la fonctionnalisation de monolithes siliciques à porosité hiérarchique et leur utilisation en tant que microréacteur en catalyse sous flux. Une synthèse reproductible de monolithes siliciques a été mise à point. La fonctionnalisation avec une variété de fonctions a été réalisée, telle que la fonctionnalisation avec des groupements aminopropyle, avec de l'oxyde d'aluminium, par incorporation des MOFs (CuBTC) et par dépôt de nanoparticules de palladium. Les monolithes fonctionnalisés ont été testés en tant que microréacteurs catalytiques sous flux pour les réactions de Knoevenagel, de Diels-Alder et de Friedländer et montrent dans plusieurs cas une augmentation de la productivité des réactions par rapport aux réacteurs batch ou à lit fixe ainsi qu'une automatisation des procédés. La transformation pseudomorphique de monolithes siliciques en monolithes zéolithiques en phase SOD et LTA a été mise a point. Nous avons ainsi montré la première utilisation d'un monolithe macroporeux à base de zéolithes en tant que microréacteur pour la synthèse de produits de chimie fine en continu. Les monolithes zéolithiques ont aussi été analysés pour l'échange d'ions en dynamique et sont prometteurs pour une application en tant que matériaux pour la décontamination d'effluents radioactifs
The aim of this work is the synthesis and the functionalization of silica monoliths with hierarchical porosity and their use as catalytic microreactors for flow-through chemistry. A reproducible synthesis of the silica monoliths was elaborated. The functionalization with a variety of functions has been performed, such as aminopropyl groups, aluminium oxide, MOFs (CuBTC), and palladium nanoparticles. These functionalized silica monoliths have been used for the Knoevenagel condensation, Diels-Alder reaction and Fiedländer reaction, where they show increasing productivities compared to classically used reactors (batch, packed-bed) and enable process automation. The pseudomorphic transformation of silica monoliths in zeolite monoliths in the SOD and LTA phase has been elaborated. We have preformed the first implementation of a macroporous zeolite monolith as microreactor for the fine chemical production in flow continuous conditions. The zeolite monoliths have been tested for dynamic ion exchange and are promising materials for the use as decontaminants of radioactive discharges

Les matériaux polymères ont connu un engouement considérable avec l’avènement de l’ère du pétrole et connaissent aujourd’hui encore un succès considérable notamment au travers de la valorisation de ressources naturelles mais également d’applications spécifiques à haute valeur ajoutée, liées à des domaines aussi divers que la chimie analytique, l’exploration spatiale, la médecine où l’enjeu premier est souvent la conception d’objet miniaturisés. Dans ce travail de thèse nous avons développé des matériaux polymères à taille micrométrique, immobilisés soit dans des microcanaux (diamètre interne = 75 µm) ou à la surface de substrats de verre (épaisseur de quelques centaines de µm). Une morphologie de type monolithique a été choisie afin de conférer auxdits matériaux des propriétés de perméabilité, résistance mécanique et thermique compatibles avec des applications dans le domaine de la chimie en flux. Afin de contrôler les propriétés d’interaction aux interfaces des matériaux, un monolithe générique, présentant des unités ester de N-hydroxysuccinimide en surface, a été préparé et fonctionnalisé à façon. Ainsi ont été immobilisés des segments moléculaires jouant le rôle de sélecteurs – pour des applications en électrochromatographie – ou de ligands de nanoparticules métalliques – pour applications en catalyse supportée – via des méthodes classiques (substituion nucléophile) ou originales (photo-addition radicalaire thiol-ène) de greffage.Les matériaux ont été caractérisés par une combinaison de méthodes spectroscopiques, microscopiques, de diffraction, de thermogravimétrie permettant de corréler les propriétés électrochromatographiques ou catalytiques avec la structure interfaciale des matériaux monolithiques. A titre d’exemples d’application, nous pouvons citer la séparation électrochromatographiques de molécules toxiques tels les polluants organiques (aniline, phénols, hydrocarbures aromatiques polycycliques, polychlorobiphényles) et les conservateurs pour les crèmes cosmétiques (parabènes), de biomarqueurs (hydrocarbures aromatiques polycycliques, bases pyrimidiques). Ces analyses ont été réalisées avec des solutions modèles de laboratoire mais aussi des matrices réelles (crèmes cosmétiques, analogues d’échantillons extraterrestres). Aussi les réactions catalytiques de réduction de nitroarènes, d’oxydation d’alcool aromatique, de couplage carbone-carbone et la détection par spectroscopie Raman exaltée de surface de pesticides (trifuraline) et d’intermédiaires de synthèse (para-nitrophénol) ont été réalisées
Polymeric materials have gained immense popularity with the golden age of petroleum and they still today meet with great success through Green polymer chemistry approaches and numerous high added value dedicated application in scientific domains such as analytical chemistry, medicine, space investigations, where one of the key for success is the design of miniaturized objects. In this contribution, micro-sized monolithic materials have been designed though either in microchannel immobilization (I.D. = 75 µm) or surface attachment on glass substrates (hundredths of microns in thickness). Polymers exhibiting monolithic morphology were considered to benefit of high permeability, mechanical and thermal resistances which are mandatory to flow chemistry applications. With the aim to control the interfacial interaction ability, a generic monolith having N-hydroxysuccinimide ester groups was used and on purpose functionalized. Molecular segments acting as selector – for electrochromatographic applications – of metal nanoparticles ligands – for supported catalysis applications – have been immobilized on the monolith surface via classical (nucleophilic substitution) or original (photo-induced thiol-ene click) grafting reactions.The so-designed materials were characterized through spectroscopic, microscopic, diffraction, thermogravimetric methods providing insight into correlation between the observed separation and catalytic abilities and the interfacial structure of the monolith. As representative examples of application, one may cite the electrochromatographic separation of toxic molecules such as organic pollutants (phenols, anilines, polycyclic aromatic hydrocarbons, polychlorobiphenyls), preservatives in cosmetics (parabens) and biomarkers (polycyclic aromatic hydrocarbons, pyrimidic bases). The analyses were conducted on model solutions and complex matrices (cosmetics, extraterrestrial analog samples). Flow catalytic reaction meant for the reduction of nitroarenes, the oxidation of aromatic alcohol, the carbon-carbon coupling and the sensitive detection of pesticides and synthesis intermediates (para-nitrophenol) have been achieved

Dans le contexte actuel de développement de nouvelles sources d'énergie non fossiles tout en minimisant l'impact environnemental, la production de carburants solaires par la valorisation des émissions anthropiques de CO2 apparaît comme une solution à fort potentiel. Le principal défi dans les processus artificiels photo-induits concerne le caractère bidimensionnel des systèmes utilisés, en raison de la faible profondeur de pénétration des photons. Ce travail de thèse se concentre sur le développement de mousses solides alvéolaires, issues de la chimie intégrative, présentant une porosité hiérarchiquement organisée. A travers l’imprégnation de précurseurs de TiO2, des photocatalyseurs autosupportés ont été synthétisés et ont montré une augmentation de la pénétration des photons d’un ordre de grandeur. D’autre part, ces solides limitent les réactions inverses par un effet de dilution, tout en assurant une sélectivité élevée envers la génération d'alcanes. Un modèle cinétique, basé sur un formalisme mixte de Langmuir-Hinshelwood et Eley-Rideal, est proposé pour décrire le comportement des matériaux
In the current context of developing novel non-fossil energy sources while minimizing the environmental impact, solar-driven-fuel-production by exploiting anthropogenic CO2 emissions appears to be a solution with great potential. The main challenge in artificial photo-induced processes concerns the two-dimensional character of the systems used, due to the low photon penetration depth. This thesis work focuses on the development of alveolar solid foams, derived from integrative chemistry and bearing a hierarchically organized porosity. By TiO2 precursor impregnation, self-standing photocatalysts were synthesized and provided a photon penetration increase by an order of magnitude. Moreover, these solids limit back-reactions by a dilution effect, while ensuring high selectivity towards alkane generations. A kinetic model, based on a mixed formalism of Langmuir-Hinshelwood and Eley-Rideal, is proposed to describe material behavior

L’objectif général de notre travail est de donner une vue d'ensemble sur les caractéristiques hydrodynamiques, les transferts de chaleur et de matière et les réactions chimiques dans les pots catalytiques monolithiques. Nous avons développé un modèle de calcul de perte de charge à travers le pot catalytique qui compose la ligne d'échappement. Ce modèle est en accord avec des mesures expérimentales. La distribution des gaz au sein du monolithe a été mesurée en fonction des paramètres géométriques du pot catalytique et du nombre de Reynolds dans le tube d'échappement. Dans le but d'uniformiser l'écoulement, l'effet d'un obstacle placé dans le divergent a été étudié. L'étude, sur le banc moteur, de la réponse thermique en régime transitoire de monolithes chimiquement actifs et inactifs nous a permis de déterminer les grands principes de mise en régime du pot sans pour cela mesurer les teneurs en polluants. Un modèle mathématique tenant compte de l'écoulement des gaz, des transferts gaz-solide et des réactions chimiques a été développé. Bien qu'il soit moins détaillé que les modèles tridimensionnels, notre modèle est particulièrement adapté pour étudier les effets des conditions opératoires, du dessin et des paramètres physico-chimiques sur le fonctionnement et l'efficacité du pot catalytique

Automotive catalytic converters are used extensively in the automotive industry to reduce toxic pollutants from vehicle exhausts. The flow across automotive exhaust catalysts is distributed by a sudden expansion and has a significant effect on their conversion efficiency. The exhaust gas is pulsating and flow distribution is a function of engine operating condition, namely speed (frequency), load (flow rate) and pressure loss across the monolith. The aims of this study are to provide insight into the development of the pulsating flow field within the diffuser under isothermal conditions and to assess the steady-state computational fluid dynamics (CFD) predictions of flow maldistribution at high Reynolds numbers. Flow measurements were made across an automotive catalyst monolith situated downstream of a planar wide-angled diffuser in the presence of pulsating flow. Cycle-resolved Particle Image Velocimetry (PIV) measurements were made in the diffuser and hot wire anemometry (HWA) downstream of the monoliths. The ratio of pulse period to residence time within the diffuser (J factor) characterises the flow distribution. During acceleration the flow remained attached to the diffuser walls for some distance before separating near the diffuser inlet later in the cycle. Two cases with J ~ 3.5 resulted in very similar flow fields with the flow able to reattach downstream of the separation bubbles. With J = 6.8 separation occurred earlier with the flow field resembling, at the time of deceleration, the steady flow field. Increasing J from 3.5 to 6.8 resulted in greater flow maldistribution within the monoliths; steady flow producing the highest maldistribution in all cases for the same Re. The oblique entry pressure loss of monoliths were measured using a one-dimensional steady flow rig over a range of approach Reynolds number (200 < Rea < 4090) and angles of incidence (0o < α < 70o). Losses increased with α and Re at low mass flow rates but were independent of Re at high flow rates being 20% higher than the transverse dynamic pressure. The flow distribution across axisymmetric ceramic 400 cpsi and perforated 600 cpsi monoliths were modelled using CFD and the porous medium approach. This requires knowledge of the axial and transverse monolith resistances; the latter being only applicable to the radially open structure. The axial resistances were measured by presenting uniform flow to the front face of the monolith. The transverse resistances were deduced by best matching CFD predictions to measurements of the radial flow profiles obtained downstream of the monolith when presented with non-uniform flow at its front face. CFD predictions of the flow maldistibution were performed by adding the oblique entry pressure loss to the axial resistance to simulate the monolith losses. The critical angle approach was used to improve the predictions, i.e. the oblique entry loss was limited such that the losses were assumed constant above a fixed critical angle, αc. The result showed that the perforated 600 cpsi monolith requires the entrance effect to be restricted above αc = 81o, while the losses were assumed constant above αc = 85o for the ceramic 400 cpsi monolith. This might be due to the separation bubble at the monolith entrance being restricted by the smaller hydraulic diameter of the perforated monolith thus limiting the oblique entry loss at the lower incidence angle.

In recent years Green Chemistry has become a central area of research for chemists working in both industry and academia. The fundamental concepts of sustainable chemistry are, among others, atom efficiency, waste prevention, use of renewable materials and innocuous solvents, as well as design of safer products. Within this context, microreactor technology offers, on the one hand, safe, environmentally benign, and high throughput processes typically intensified by a fast postreaction phase (workup and purification) and direct scalability; on the other hand, asymmetric organocatalysis allows for new and unique opportunities towards efficient and highly stereoselective metal-free catalytic syntheses. In the first part of this thesis project it has been carried out the synthesis of new heterogeneous organocatalysts for their ultimate utilization in continuous-flow processes. Precisely, proline-like mimetics and thiazolium salt pre-catalysts have been immobilized on silica and polystyrene macroporous supports, respectively; next, these functionalized solid materials have been employed as packing material for the fabrication of fixed-bed microreactors in the form of either packed or monolithic columns. During this research, it has been demonstrated that operation of this type of organocatalytic microreactors results in flow processes with levels of stereoselectivity comparable to those of the corresponding homogeneous batch processes, allowing at the same time productivity enhancements thanks to the higher long-term stability of the heterogeneous organocatalytic species in flow regime. In the second part of this thesis project, the same techniques of support functionalization have been employed to prepare perfluorinated stationary phases for the determination of perfluorinated compounds (PFCs). These are emerging pollutants widely spread in the environment. They can be found in soils, sediments, superficial waters, particulate matter, as well as in animal and human tissues or organs. PFC are characterized by environmental persistence and have negative side effects for the biota where they accumulate. The chromatographic behavior of perfluorinated acid pollutants have been investigated on the basis of the specific fluorine-fluorine interactions (fluorophilicity) occurring between these analytes and the perfluoroalkyl groups of the newly prepared stationary phases. It has been demonstrated that the retention profile of perfluorinated acids is dependent on the composition of the mobile phase, thus permitting the use of the prepared fluorinated stationary phases as means of pre-concentration of PFCs from environmental and biological matrices.

Automotive catalytic converters are increasingly used to reduce emissions from internal combustion engines to comply with emission regulations. Maldistributed flow across the catalyst affects its warm up, light off time, ageing, and conversion efficiency. This thesis concerns flow distribution in automotive catalytic converters and methods to improve CFD predictions. Previous studies showed that modelling the monolith flow resistance using the Hagen- Poiseuille’s formulation under predicted flow maldistribution. The predictions were improved by incorporating an additional pressure loss term V2 2 1  , where V is transverse velocity just upstream of a monolith channel, for oblique entry of the flow into the monolith known as the entrance effect. Further improvement was obtained by incorporating the critical angle of attack method. However, there was no experimental evidence to support these oblique entry loss formulations. There also remained the possibility that under prediction of flow maldistribution might be due to the failure to predict flow in the diffuser accurately. A one-dimensional oblique angle flow rig was designed and built to measure the effect of oblique entry flow losses in monoliths. Experiments were performed at different angles of attack (α), using different lengths of substrate and a methodology was developed to obtain the oblique flow entrance losses. The results showed that the pressure loss attributed to the entrance effect increased with the angle of attack. The entrance effect was also found to be dependent on channel Reynolds number and substrate length. The theoretical assumption of V2 2 1  predicts accurately at low Reynolds number but looses its validity at high Reynolds number. From the experimental studies, an improved correlation for the entrance effect has been derived as a function of major controlling variables, i.e., angle of attack, length of the substrates and Reynolds number. A two-dimensional rig was designed to measure the flow field using PIV in a 2-D diffuser placed upstream of two different length substrates. The results showed that the flow in a wide angle diffuser consisted of a central core, free shear layer and recirculation regions. The near-field region was found similar to that of a plane jet. The flow field was found to be independent of Reynolds number. Increasing the substrate length resulted in a flattening of the axial profiles close to the substrate face. A CFD study was undertaken to predict maldistributed flow at the exit of the substrate for an axisymmetric catalyst model by incorporating the measured entrance effect correlation. A fixed critical angle of attack (αc,F) approach was used whereby the entrance effect is assumed constant for α>αc,F. Incorporating the entrance effect with αc,F= 810 improved the prediction of maldistribution in the flow profiles. A 2-D CFD study was undertaken to predict the flow distribution in the diffuser and downstream of the substrate. A comparison of the CFD predictions in the diffuser using different turbulence models showed that all the turbulence models used in this study over predicted the width of the central core region and the V2F turbulence model gave velocity predictions that compared best with PIV. Incorporating the entrance effect improved the predictions close to the diffuser-substrate interface and downstream of the substrate.

Heavy-duty diesel truck engines are routinely idled at standstill to provide cab heating or air conditioning, and in addition to supply electricity to comfort units such as radio and TV. Idling is an inefficient and unfavorable process resulting in increased fuel consumption, increased emissions, shortened engine life, impaired driver rest and health, and elevated noise. Hydrogen-fueled, polymer-electrolyte fuel-cell auxiliary power unit (PEFC-APU) as a silent external power supply, working independently of the main engine, is proposed as viable solution for better fuel economy and abatement of idling emissions. In a diesel PEFC-APU, the hydrogen storage problem is circumvented as hydrogen can be generated onboard from diesel by using a catalytic reformer. In order to make catalytic diesel PEFC-APU systems viable for commercialization research is still needed. Two key areas are the development of reforming catalyst and reformer design, which both are the scope of this thesis. For diesel-reforming catalysts, low loadings of Rh and RhPt alloys have proven to exhibit excellent reforming and hydrogen selectivity properties. For the development of a stable reforming catalyst, more studies have to be conducted in order to find suitable promoters and support materials to optimize and sustain the long-term performance of the Rh catalyst. The next step will be full-scale tests carried out at realistic operating conditions in order to fully comprehend the overall reforming process and to validate promising Rh catalysts. This thesis can be divided into two parts; the first part addresses the development of catalysts in the form of washcoated cordierite monoliths for autothermal reforming (ATR) of diesel. A variety of catalyst compositions were developed containing Rh or RhPt as active metals, CeO2, La2O3, MgO, Y2O3 as promoters and Al2O3, CeO2-ZrO2, SiO2 and TiO2 as support materials. The catalysts were tested in a bench-scale reactor and characterized by using N2-BET, XRD, H2 chemisorption, H2-TPR, O2-TPO, XPS and TEM analyses. The second part addresses the development and testing of full-scale reformers at various realistic operating conditions using promising Rh catalysts. The thesis shows that a variety of Rh on alumina catalysts was successfully tested for ATR of diesel (Papers I-IV). Also, zone-coating, meaning adding two washcoats on specific parts of the monolith, was found to have beneficial effects on the ATR catalyst performance (Paper II). In addition, RhPt supported on CeO2-ZrO2 was found to be one of the most active and promising catalyst candidates for ATR of diesel. The superior performance may be attributed to higher reducibility of RhiOx species and greater dispersion of Rh and Pt on the support (Paper IV). Finally, two full-scale diesel reformers were successfully developed and proven capable of providing high fuel conversion and hydrogen production from commercial diesel over selected Rh catalysts (Papers II-III, V-VI).
QC 20110418

Abstract The harmful emissions of chlorinated volatile organic compounds (CVOCs) originate only from man-made sources. CVOCs are used in a variety of applications from pharmaceuticals production to decaffeination of coffee. Currently, CVOC emissions are limited by strict legislation. For these reasons, efficient CVOC abatement technologies are required. Catalytic oxidation is very promising option for this purpose, since catalysts can be tailored to each case to maximize the efficiency and minimize the formation of unwanted products, such as dioxins or Cl2. The goal of this thesis was to study the role of the physico-chemical properties of catalysts in dichloromethane (DCM) oxidation. To reach the aim, several catalytic materials were prepared and characterized, and their performance was tested in total oxidation of DCM. The catalytic materials used were powders of four single metal oxides (γ-Al2O3, TiO2, CeO2, MgO), three mixed oxides (Al2O3-xSiO2) washcoated on a cordierite monolith and four active phases (Pt, Cu, V, Mn). At first, support properties were studied. It was found that the DCM conversion and HCl production are dependent on support acidity when the studied single oxides are considered. The best DCM conversions and HCl yields were observed with the support having the highest total acidity (γ-Al2O3). Further, the quality of the by-products formed was dependent on the type of the acid sites present on the support surface. Secondly, the impregnation of the active compound was observed to improve the selectivity of the material. From the tested active phases, Pt presented the best performance, but also V2O5 and CuO showed almost equal performances. Especially CuO supported on γ-Al2O3, that had less formation of by-products and is less toxic than V-containing oxides, seems to be a promising alternative to Pt. Concerning stability, no deactivation was observed after 55h of testing of Pt/Al2O3. Furthermore, in the used reaction conditions, the formation of CuCl2 is not thermodynamically favoured. Finally, the good characteristics of the powder form catalysts were successfully transferred to the monolith. The performance of the Pt/90Al2O3-10SiO2 catalyst in DCM oxidation was improved when the channel density was increased due to an increase in geometric surface area and mechanical integrity factor, and a decrease in open fraction area and thermal integrity factor
Tiivistelmä Haitallisten kloorattujen orgaanisten yhdisteiden (CVOC) päästöt ovat ihmisten aiheuttamia. CVOC-yhdisteitä käytetään mm. liuottimina lääkeaineiden valmistuksessa ja kofeiinin poistossa. Nykyisin CVOC-päästöjä rajoitetaan tiukalla lainsäädännöllä. Näistä syistä tehokas CVOC-yhdisteiden käsittelymenetelmä on tarpeen. Katalyyttinen hapetus on hyvä vaihtoehto tähän tarkoitukseen, koska katalyytit voidaan räätälöidä niin, että puhdistuksen tehokkuus saadaan maksimoitua samalla kun ei-haluttujen tuotteiden, kuten dioksiinit ja kloorikaasu, muodostuminen voidaan minimoida. Tämän väitöskirjatyön tavoitteena oli selvittää katalyyttien fysikaalis-kemiallisten ominaisuuksien yhteyksiä dikloorimetaanin (DCM) hapetukseen. Tavoitteen saavuttamiseksi valmistettiin useita katalyyttejä, jotka karakterisoitiin ja testattiin DCM:n kokonaishapetuksessa. Työssä tutkittiin neljää jauhemaista metallioksidia (γ-Al2O3, TiO2, CeO2 ja MgO), kolmea metallioksidiseosta (Al2O3-xSiO2), jotka pinnoitettiin kordieriittimonoliitille, sekä neljää aktiivista ainetta: Pt, Cu, V and Mn. Aluksi työssä keskityttiin tukiaineiden ominaisuuksiin. Työn tulokset osoittivat, että DCM:n konversio ja HCl:n tuotanto ovat riippuvaisia tukiaineen happamuudesta. Paras tulos saavutettiin alumiinioksidilla, jolla oli korkein kokonaishappamuus. Lisäksi havaittiin, että sivutuotteiden laatu riippuu tukiaineen pinnalla olevien happopaikkojen tyypistä. Aktiivisen aineen impregnointi tukiaineeseen paransi materiaalin selektiivisyyttä. Tutkituista aineista Pt osoittautui parhaimmaksi, mutta myös V2O5 ja CuO olivat lähes yhtä hyviä. Erityisesti CuO-katalyytti, joka tuotti vähemmän sivutuotteita ja joka on materiaalina vähemmän haitallinen kuin V2O5, osoittautui lupaavaksi jalometallikatalyyttien korvaajaksi. Materiaalien stabiilisuuteen liittyen Pt/Al2O3-katalyytin toiminnassa ei havaittu muutoksia 55 tunnin testauksen jälkeen. Lisäksi CuCl2:n muodostuminen ei mallinnuksen mukaan ole termodynaamisesti todennäköistä tutkituissa reaktio-olosuhteissa. Jauhemaisen katalyytin hyvät ominaisuudet pystyttiin pinnoituksessa siirtämään monoliittirakenteiseen katalyyttiin. Pt/90Al2O3-10SiO2 -katalyytin aktiivisuus DCM:n hapetuksessa tehostui, kun monoliitin aukkoluku kasvoi aiheutuen suuremmasta geometrisestä pinta-alasta ja mekaanisesta eheystekijästä sekä pienemmästä avoimen pinnan osuudesta ja termisestä eheystekijästä

Des molécules oxygénées ont démontré des propriétés de co-carburant diesel pouvant réduire les émissions nocives des moteurs diesel. Ainsi la synthèse de nouvelles molécules oxygénées à partir de bioéthanol et/ou de glycérol a été mise en œuvre. L'obtention de diéthoxyéthane et de butanol à partir d'éthanol en synthèse « one-pot » a été menée sur catalyseur oxydes mixtes ainsi que sur oxydes mixtes supportés sur nanotubes de carbone. D'autre part, l'éthérification du glycérol par l'éthanol a ensuite été étudiée sur catalyseur acide hétérogène en vue d'obtenir le 1-éthoxy-2,3-propanediol de manière sélective. Ce mono-éther est ensuite utilisé pour une réaction d'acétalisation avec l'acétaldéhyde pour donner un mélange dioxane/dioxolane adapté à une utilisation co-carburant diesel. Les résultats obtenus pour l'éthérification ont permis de mettre en avant un mécanisme réactionnel et de définir les caractéristiques qu'un catalyseur « idéal » doit posséder. La réaction d'acétalisation avec l'acétaldéhyde a conduit à l'utilisation d'un catalyseur innovant synthétisé au laboratoire : les monolithes siliciques fonctionnalisés. Les nombreuses propriétés de ces matériaux ouvrent de multiples perspectives pour la réaction étudiée et pour d'autres réactions de chimie organique
Oxygenates have shown interesting properties as diesel fuel additives in reducing the emissions of a diesel engine. The synthesis of new oxygenate molecules from glycerol and bioethanol has been then studied. The one pot synthesis of diethoxyethane and butanol from ethanol only as been done on mixed oxide catalysts as well as on mixed oxide supported on carbon nanotubes. Etherification of glycerol with ethanol has also been studied on various heterogeneous acid catalysts in order to obtain selectively 1-ethoxy-2,3-propanediol. This mono-ether has then been used for an acetalization reaction with acetaldehyde to give a mixture of dioxane/dioxolane products well suited for a diesel blending. Results obtained for the etherification reaction allowed us to propose a reaction mechanism and define the characteristics of an “ideal” catalyst. Acetalization reaction with acetaldehyde led us to use a new type of catalyst synthesized in the laboratory: functionalized silica monoliths. The various interesting properties of those materials opened multiple developments for the studied reaction as well as for a large number of organic chemistry reactions

Considerable research is being carried out into the parameters that affect catalyst performance in order to meet the latest emission regulations. The conversion efficiency and the durability of automotive catalytic converters are significantly dependent on catalyst flow performance. Related investigations are commonly conducted using CFD techniques which represent an inexpensive and fast alternative to experimental methods. This thesis focuses on the flow performance of automotive catalytic converters using both experimental and computational techniques. The work describes the effects of inlet flow conditions on catalyst performance, the application of radial vanes to catalyst systems and the refinement of the CFD flow model which increases the accuracy of the predicted catalyst flow performance. the effects of inlet flow conditions on the flow maldistribution across the catalyst face and the total pressure loss through the system were assessed using a steady air flow rig. Tests were conducted over a range of Reynolds numbers typically encountered in automotive catalytic converters using a uniform and a fully-developed inlet flow condition. The results showed that the flow maldistribution significantly increases with Reynolds number notably in wide-angled diffusers. The catalyst flow performance is considerably improved when the inlet flow is uniform rather than fully-developed, the non-dimensional total pressure loss is reduced by 8% at Re=60000 and the flow maldistribution across the catalyst face is decreased by 12.5% and 15% respective Reynolds numbers of 30000 and 60000 when using a 60 degree diffuser. The total pressure loss through the system was found to be mostly associated with the monolith brick resistance. When the flow maldistribution is approximately 2, the pressure loss across the monolith brick represents 80% of the system pressure loss. The flow maldistribution across the catalyst face was improved by locating a system of radial splitters in the diffuser. The optimum flow performance was found to be a complex function of the vane design. A maximum improvement in the flow maldistrution indices M and Mi of 25% and 50% respectively was achieved at the expense of an increase in total pressure loss of 13.5% at Re = 60000. Both CFD and flow visualisation techniques were used as an aid to interpreting the flow field in the diffuser. Although a qualitative agreement was obtained using CFD, the flow maldistribution across the catalyst face was underpredected by up to 20%. The accuracy of the flow predictions was significantly improved by investigating the flow field in the monolith channels. Flow recirculation occurs in the channel entry length when the flow approaches the monolith channels at an angle which induces an additional implemented into four models of the flow through axisymmetric catalyst assemblies using various diffuser geometries and inlet flow conditions. By including the flow entrance effects in the porous media approach, the flow maldistribution was predicted within 8% instead of 15% when these effects are neglected. Further investigation of the flow in the monolith channels will be required to accurately model three-dimentional flows (racetrack catalysts) and to include various channel geometries and system flow rates.

The immobilization of metal NPs and metal single sites on silica support materials offers an interesting approach to heterogeneized catalysts for a multitude of different reactions. Selective hydrogenation reactions of prochiral substrates, such as (hetero-)aromatics, can be catalyzed by heterogeneized “hybrid catalysts” of the type RhI-Pd0/SiO2, consisting of silica-supported PdNPs and chiral Rh(I) phosphine single sites. These new “hybrid catalysts” were reported in the recent years, revealing the synergetic effect between Pd and Rh. Regarding the hydrogenation of benzene/toluene, it could be shown that RhI-Pd0/SiO2 are 4 times more active than Pd0/SiO2. In particular, the scope of this work was the extension of the “hybrid catalysts” by the use of chiral phosphine ligands. PdNPs were immobilized onto various mesoporous silica supports, having an ordered (e.g. MCM-41, SBA-15) or a non-ordered (e.g. Davisil B, Davison 62) structure, both in powdery form and as monoliths. Different immobilization methods were tested (impregnation, ionic exchange, CVD), whereupon CVD proved to be a promising procedure, giving high Pd loadings up to 1.95 wt % (expected: 2 wt %). Moreover, this method was suitable for both powdery silica materials and silica monoliths. Silica-supported chiral Cu(I) complexes of the type [CuI(PC-L*)]CF3SO3/SiO2 can be applied in the asymmetric cyclopropanation of -methyl styrene with ethyl diazoacetate (EDA). Regarding the different mesoporous ordered- and non-ordered silica supports (MCM-41, SBA-15, Davisil B, Aerosil, basic silica), SBA-15 turned out to be the most-suitable one, giving excellent Cu loadings up to 1.79 wt %. The application of the [CuI(PC-L*)]CF3SO3/SiO2 catalysts gave the cyclopropanes in high yields (83 %). In this context, the recyclability of [CuI(PC-L*)]CF3SO3/SiO2 could be proven. Silica monoliths are very advantageous and thus gladly used as support material: Besides their easy handling, they allow to work in flow conditions without packing a reactor. Within this work, silica monoliths were grafted and subsequently applied in the dehydration of fructose to 5-hydroxymethylfurfural (HMF). It was shown that the reaction works in batch as well as in flow, both homogeneously (using the sole unsupported grafting agent) and heterogeneously (using blank or grafted silica monoliths).

碩士
國立成功大學
化學工程學系碩博士班
93
Monolithic catalysts have been widely applied to abate exhaust gases. Because of the shape, the honeycomb gives a low pressure drop and its catalyst layer does not attrition the fluid.It can be used as a reactor directly.On the other hand,nano-particle technology is appropriate for producing high performance catalysts. The nano- catalysts prossess a markedly higher activity and selectivity compared with the conventional ones. The nano-catalysts can be also used for reactions at relativity low temperatures, thereby reducing energy consumption. 　In this study, for catalyzing the reduction of nitric oxide with hydrogen as a reducing agent, the cordierite monolith was coated with several kinds of supported metal oxides first. Then the activities of the prepared catalysts were evaluated by a monolithic reactor.The best catalyst was screened from those prepared. The causes for different activities were also closely examined basing on the result of catalyst characterization. 　Experimental results indicate that active species of coating layer,support of coating layer,method of preparing the support, calcination temperature,and pretreatment all are important factors affecting catalyst activity. The results of activity test indicate that coating a γ-alumina layer with sol-gel coating method and loading 14 wt% copper with deposition-precipitation method give the highest activity. 　The surface area of γ-Al2O3/monolith,of which γ-Al2O3 was made by sol-gel coating and calcined at 500℃, is the largest and the catalyst thus prepared is more active than those prepared by other methods.The XRD patterns, reveal that the particle-size of alumina prepared with sol-gel coating is smaller then those prepared by another method. The SEM graphs show that the sizes of γ-Al2O3 particles prepared by various methods are all in the nano range. 　At the end of this study, the activities and stabilities of the powder catalyst and the monolithic catalyst were compared. The results show that monolithic catalyst has a better performance and hence has a potential for being applied to air pollution control.

碩士
高苑科技大學
高分子環保材料研究所
94
In this study, the performance of nanosized CeO2 used as catalysts for the catalytic incineration of aromatic hydrocarbons was investigated. We tested the efficacy of seven metal oxide catalysts in the catalytic incineration of aromatic hydrocarbons and found CeO2 to be the most active of the seven. With the use of CeO2, complete oxidation of toluene was achieved at 240 ℃. There was a similar outcome in the incineration of p-xylene, whereas benzene was more refractory. In preparation of the CeO2 catalyst, four different methods were evaluated; a redox reaction in hydrogen peroxide was found to produce the most active catalyst. This is because CeO2 prepared using this method (designated as CeO2-A) had the smallest crystallite size and the largest BET surface area, both characteristics that confer higher activity. O2-TPD and toluene-TPD also demonstrated the superior activity of the CeO2-A catalyst, as it was best able to adsorb both toluene and O2. The effect of calcination temperature was also assessed to find the optimal preparation conditions. CeO2 calcined at 500 ℃ was the most active catalyst; its higher activity can be attributed to its smallest crystallite size and hence largest surface area. In the reaction, a higher reaction temperature was necessary for 100% conversion of toluene at higher values of weight hourly space velocity (WHSV) and higher toluene concentrations. For the catalytic incineration of aromatic hydrocarbons, nanosized CeO2 was coated to honeycomb support by redox reaction in hydrogen peroxide and the used as the support to prepare several kinds of supported metal-oxide catalysts by incipient wetness impregnation method. Then the activities of the honeycomb catalysts were evaluated by a fixed bed reactor. Experimental results indicate that active species of coating layer, calcination temperature are important factors affecting catalyst activity. The results of activity test indicate that coating a CeO2 layer with redox reaction in hydrogen peroxide coating method and loading 0.3 wt% palladium with incipient wetness impregnation method give the highest activity. At the end of this study, the activities and stabilities of the powder catalyst and the monolithic catalyst were compared. The results show that monolithic catalyst has a better performance and hence has a potential for being applied to air pollution control.

Among the various heterogeneous catalytic reactions three way catalysis (TWC), catalytic combustion of hydrogen, water gas shift reaction (WGS) and preferential oxidation of CO (PROX) in the hydrogen rich stream are some of the important reactions receiving the attention presently. Three-way catalysis (TWC) involves simultaneous removal of the three pollutants (i.e., CO, NOx, and HCs) from the automobile exhaust. Catalytic combustion of hydrogen by oxygen or hydrogen-oxygen recombination reaction is an industrially important reaction. It has variety of application such as in sealed lead acid batteries and nuclear reactors. Water gas shift (WGS) reaction is of specific importance to produce hydrogen from carbonaceous material. PROX is an important step to further purify hydrogen produced form WGS. Hydrogen purified using PROX can be directly fed to polymer electrolyte membrane fuel cells. By and large, noble metals Pt, Pd, Rh, Ru and some of their alloys are dispersed on oxide or high surface area carbon are the active catalysts. An alternative approach can be to make Pt2+, Pd2+, Rh3+, Ru4+ ions substituted in reducible support such as CeO2, Ce1-xTixO2-δ and TiO2 to increase the dispersion and bring down the cost. In this thesis we have followed this new approach and show that noble metal ionic catalysts are superior to noble metal nano particles. In the 1st chapter we present an overview of heterogeneous catalysis and important heterogeneous catalytic reactions. Monolithic catalyst and various ways to coat catalysts for application have been reviewed. Metal-support interaction till date is also reviewed. In the 2nd chapter, synthesis of noble metal ionic catalysts by solution combustion method is described. Coating of washcoat and active catalyst phase over ceramic honeycomb by a new combustion method is described. Solution combustion reaction and characterization of the catalyst by x-ray diffraction, x-ray photoelectron spectroscopy, temperature programmed reduction and reaction is given. We have fabricated experimental systems to carryout catalytic reaction and in this chapter they have been presented. In the 3rd chapter, we report a new process of coating of active exhaust catalyst over -Al2O3 coated cordierite honeycomb. The process consists of (a) growing  -Al2O3 on cordierite by solution combustion of Al(NO3)3 and oxylyldihydrazide (ODH) at 600 0C. Active catalyst phase, Ce0.98Pd0.02O2- is coated on - Al2O3 coated cordierite again by combustion of ceric ammonium nitrate and ODH with 1.2  10-3 M PdCl2 solution at 500 0C. In this way a coat layer over cordierite ceramic has been achieved and catalyst has the active sites in the form of Pd2+ ions rather than Pd metal. Weight of the active catalyst can be varied from 0.02 to 2 wt% which is sufficient but can be loaded even up to 12 wt% by repeating dip dry combustion [1]. Adhesion of catalyst to cordierite surface is via oxide growth on oxide ceramic which is very strong. 100 % conversion of CO is achieved below 80 oC at a space velocity of 880 h-1. At much higher space velocity of 21000h-1, 100 % conversion is obtained below 245 oC. Activation energy for CO oxidation is 8.4 kcal/mol. At a space velocity of 880 h-1 100% NO conversion is attained below 185 oC and 100 % conversion of ‘HC’(C2H2) below 220 oC. At the same space velocity 3-way catalytic performance over Ce0.98Pd0.02O2- coated monolith shows 100% conversion of all the pollutants below 220 o C with 15% excess oxygen. Catalytic activity of cordierite honeycomb coated by this new coating method for the oxidation of major hydrocarbons in exhaust gas is discussed further in this chapter. ‘HC’ oxidation over the monolith catalyst is carried out with a mixture having the composition, 470 ppm of both propene and propane and 870 ppm of both ethylene and acetylene with the varying amount of O2. 3-way catalytic test is done by putting hydrocarbon mixture along with CO (10000ppm), NO (2000ppm) and O2 (15000ppm). Below 350 oC full conversion is achieved [2]. A comparison of the results shows that Ce1-xPdxO2-δ far superior to other catalysts. In this method, handling of nano material powder is avoided. In the 4th chapter we present a detailed study on the catalytic combustion of hydrogen by oxygen (hydrogen oxygen recombination reaction). Ever since Michel Faraday showed H2 + O2 recombination reaction over platinum metal plates, Pt metal has remained the only room temperature recombination catalyst. In search of an alternative catalyst, we discovered a new Pt free Ti0.99Pd0.01O2- compound which shows high rates of this reaction above 45 oC compared to Ce0.98Pt0.02O2-, Pt/Al2O3 and Pd/Al2O3. High rates of H2+O2 recombination over Pt and Pd ion respectively in CeO2 and TiO2 is due to the protonic type H2+ adsorption on Pt2+ or Pd2+ and dissociative chemisorption of O2 on the electron rich oxide ion vacancies [3]. In the case of Ce0.98Pt0.02O2-, H2/Pt ratio in a TPR experiment is ~2.3 at 0 oC. In the case of Ti0.99Pd0.01O2- also, H2 adsorption occurs below 0 oC and H2 / Pd ratio is ~2.2. Thus, more than 4-5 H atoms are adsorbed per metal ion. This is attributed to hydrogen spillover. H2 is known to be adsorbed as hydride ion (H-) over Pt, Pd, Rh, Ru, Os and Ir metals. Proton NMR studies of H2 adsorbed on Pd metal have shown upfield i.e. negative shift of 12 ppm with respect to TMS. We have studied proton NMR of Ti0.99Pd0.01O2- + H2 which show a downfield shift of 11.35 ppm confirming H+ or H2+ kind of species over Pd2+ ion in Ti0.99Pd0.01O2-. In Ce0.98Pt0.02O2- also H2 adsorption led to H2+ like species observed at 8 ppm and DFT calculations indeed showed H2+ kind species. H2+ is a precursor for dissociation and can readily induce O2 dissociation leading to high rates of recombination. In the 5th chapter we report water gas shift reaction (WGS) and preferential oxidation of CO (PROX) over Ti0.99Pt0.01O2-, Ce0.83Ti0.15Pt0.02O2- and Ce0.98Pt0.02O2-δ. The water gas shift reaction (WGS) is an important reaction to produce hydrogen. In this study, we have synthesized nano crystalline catalysts where Pt ion is substituted in the +2 state in TiO2, CeO2 and Ce1-xTixO2-δ. The catalysts have been characterized by X-ray diffraction and X-ray photoelectron spectroscopy (XPS) and it has been shown that Pt2+ ions in these reducible oxides of the form Ti0.99Pt0.01O2-, Ce0.83Ti0.15Pt0.02O2- and Ce0.98Pt0.02O2-δ are highly active. These catalysts were tested for the water gas shift reaction both in presence and absence of hydrogen. It is shown that Ti0.99Pt0.01O2- exhibits higher catalytic activity than Ce0.83Ti0.15Pt0.02O2- and Ce0.98Pt0.02O2-δ [4]. Further, experiments were conducted to determine the deactivation of these catalysts by performing the daily startup and shutdown of the reactor for over 24 hours. There was no sintering of Pt and no carbonate formation and, therefore, the catalyst did not deactivate even after prolonged reaction. There was no carbonate formation because of the highly acidic nature of Ce4+, Ti4+ ions in the catalysts. Further, PROX activity of these catalysts has been studied. Ce0.83Ti0.15Pt0.02O2- and Ce0.98Pt0.02O2-δ showed high activity, large operating temperature window and low working temperature proving them to be highly effective PROX catalysts. In the 6th chapter we study the electrocatalysis of formic acid electro-oxidation and simultaneously mapping the electronic states of the electrodes by X-ray photoelectron spectroscopy (XPS). Ionically dispersed platinum in Ce1-xPtxO2-δ and Ce1-x-yTiyPtxO2-δ is very active towards oxygen evolution and formic acid oxidation. Higher electro-catalytic activity of Pt2+ ions in CeO2 and Ce1-xTixO2 compared to Pt0 in Pt/C is due to Pt2+ ion interaction with the supports, CeO2 and Ce1-xTixO2 respectively [5]. Further, ionic platinum does not suffer from CO poisoning effect unlike Pt0 in Pt/C. Utilization of lattice oxygen from the electrodes during the reaction has been demonstrated. This lattice oxygen exchange is responsible to convert CO to CO2 in the lower potential region to remove CO poisoning effect. In 7th chapter we repeat our study on the noble metal ion reducible oxide interaction in Ce1-xPtxO2- and Ce1-xPdxO2- (x= 0.02) system by a novel electrochemical method combined with XPS. Working electrodes made of CeO2 and Ce0.98Pt0.02O2- mixed with 30% carbon are cycled between 0.0-1.2 V in potentio-static (chronoamperometry) and potentio-dynamic (cyclic voltametry) mode with reference to saturated calomel electrode (SCE). Reversible oxidation of Pt0 to Pt2+ and Pt4+ state due to the applied positive potential is coupled to simultaneous reversible reduction of Ce4+ to Ce3+ state. CeO2 reduces to CeO2-y (y= 0.35) after applying +1.2 V which is not reversible. But Ce0.98Pt0.02O2- reaches a steady state with Pt2+: Pt4+ in the ratio of 0.60: 0.40 and Ce4+: Ce3+ in the ratio of 0.55: 0.45 giving a composition Ce0.98Pt0.02O1.74 at 1.2 V which is reversible [6]. Composition of Pt ion substituted compound is reversible between Ce0.98Pt0.02O1.95 to Ce0.98Pt0.02O1.74 within the potential range of 0.0-1.2 V. Thus, Ce0.98Pt0.02O2- forms a stable electrode for oxidation of H2O to O2 unlike CeO2. A linear relation between oxidation of Pt2+ to Pt4+ with simultaneous reduction of Ce4+ to Ce3+ is observed demonstrating Pt-CeO2 metal support interaction is due to reversible Pt0/Pt2+/Pt4+ interaction with Ce4+/Ce3+ redox couple. Similar studies have been performed with Ce0.98Pd0.02O2- catalyst to show the redox coupling between Pd2+/Pd0 and Ce4+/Ce3+ redox couples. We expect similar redox coupling for Pd, Pt ions substituted TiO2, and Ce1-xTixO2. In the final chapter 8, a critical review and conclusion on the results presented in the thesis is presented. The combustion synthesized catalysts reported in this thesis stabilizes the Pt and Pd metals in their ionic state rather than zero valent metallic state. Thus, the catalysts are uniform solid catalysts. High activity and stability of these catalysts are shown to be due to the electronic interaction between noble metal ions and the reducible oxide. Redox couples Pt0/Pt2+, Pt2+/Pt4+ and Pd0/Pd2+ interact with Ce4+/Ce3+, Ti4+/Ti3+ couples such that metal is oxidized and the support is reduced. This has been established in the thesis by a combined use of electrochemistry and XPS thus solving a long standing problem of metal support interaction in catalysis. We hope that the results presented in the thesis is a worthwhile contribution to catalysis. (For mathematical equations pl refer pdf file.)

Thesis (M.S.) -- University of Tennessee, Knoxville, 2006.
Title from title page screen (viewed on Sept. 18, 2006). Thesis advisor: Ke Nguyen. In abstract [gamma] is lower case Greek letter. Vita. Includes bibliographical references.

Miniaturisation of reactions to the sub-millilitre scale, through the use of microreactor technology, has the potential to reduce costs by drastically reducing reaction times, improving yields and selectivities, as well as decreasing the environmental impact by reducing reagent and solvent use. Further improvements can be achieved by utilising heterogeneous and supported catalysts within microreactors in order to increase reaction efficiency, reduce energy requirements, and simplify product purification. This should also enable the integration of microreactors with other existing microfluidic technologies allowing synthesis, purification, analysis, and bio-testing to be performed on a single device in an automated fashion. In this work, novel microreactors were fabricated utilising porous polymer monoliths (PPM's) prepared in situ within microfluidic devices as a support for the immobilisation of palladium complexes. Poly(glycidyl methacrylate-co-ethylene glycol dimethylacrylate) and poly(chloromethylstyrene-co-divinylbenzene) monoliths were prepared by either thermal or UV initiated radical polymerisation in several formats, including capillary, microchip, and column using both glass and polymer substrates. This required the development of new methods for anchoring PPM within polymer substrates with poor transmission in the deep UV region, which is necessary for photografting, thus enabling the use of polymer substrates with greater thermal resistance. The development of polymeric microreactors was pursued as mass production of microfluidic devices with multiple components is considerably easier and more economical compared to other substrates. Additionally, conditions were developed to allow the formation of PPM in columns with an internal diameter (ID) greater than 1 mm without the need for external compression to avoid shrinkage. The preparation of PPM using light emitting diode light sources was investigated with the aim of reducing the cost associated with development of photoinitiated PPM's, enabling greater access to this technique. The PPM's were utilised to immobilise ligands that will bind palladium, 5-hydroxy-1,10- phenanthroline, 5-amino-1,10-phenanthroline, and an N-methylimidazolium salt. In order to demonstrate the feasibility of this technology, the Suzuki-Miyaura coupling of iodobenzene and p-tolylboronic acid was performed under continuous flow in the reactors, which produced quantitative yields with less than 0.01% of the immobilised palladium leached over a 24 h reaction period. This is the first reported used on a polymer microchip for supported Suzuki-Miyaura catalysis and also the first demonstration of non-room temperature supported palladium catalysis within a polymer microreactor. Novel technology was developed to allow easy interfacing with a broad range of microchips and for producing PPM in batch via UV initiation using low intensity light sources.

The diesel engine is growing in popularity due to its energy efficiency and solving the emissions issues associated with diesel engine exhaust would clear the way for further growth. The key pollutants are NOx, particulate matter and unburned hydrocarbons. Selective catalytic reduction (SCR) catalysis is likely the best choice for NOx control. In SCR, NH3 selectively reacts with NOx to form N2 – the selectivity refers to NH3 reacting with NOx instead of the abundant O2. Urea is used as the NH3 source, being injected into the exhaust as an aqueous solution where the urea decomposes and NH3 is generated. Spatial resolution characterization techniques have been gaining attention in the catalysis field because of the higher level of information provided. In this thesis, a new spatial resolution technique, called SpaciFTIR (spatially-resolved, capillary-inlet Fourier transform infra-red spectroscopy), was developed, which overcomes the interference of water in the detection of NH3 in an earlier developed technique, SpaciMS (spatially-resolved, capillary-inlet mass spectrometry). With the new test method, three SCR topics were addressed. First, the three key SCR reactions were spatially resolved. These are the standard SCR reaction (2NO + 2NH3 + 1/2O2 = 2N2 + 3H2O), the fast SCR reaction (NO + NO2 + 2NH3 = 2N2 + 3H2O), and NO2-SCR, (6NO2 + 8NH3 = 7N2 + 12H2O). Results show that in the presence of NO2, but at a NO2/NOx ratio < 0.5, the fast SCR reaction proceeds followed by the standard SCR reaction, i.e. in series. If the NO2/NOx ratio exceeds 0.5, the NO2-SCR and fast SCR reactions occur in parallel. Compared to the standard integral test method, this spatial resolution technique clearly showed such trends. Secondly, the spatial resolution technique was used to characterize the effects of thermal aging on catalyst performance. It was found that for a highly aged catalyst, there was a radial activity profile due to an inhomogeneous temperature distribution in the process of aging. Aging effects on various key SCR reactions, i.e. NO oxidation, NH3 oxidation, and the reduction reactions, were studied. Last but not least, for the purpose of passive SCR system development, transient NH3 storage profiles along the monolith channel were measured with SpaciFTIR. Passive SCR is a system where the NH3 is generated on an upstream catalyst, such as a three-way catalyst or lean-NOx trap, instead of via urea injection. In such a system, NH3 is therefore not constantly being fed to the SCR catalyst, but “arrives” in pulses. Factors such temperature, NH3 concentration, pulsing time, flow rate and thermal aging were investigated. For the first time, NH3 migration was observed and its effect on SCR reactions along the length of catalyst was studied.

The ability to resolve reactions within a monolith spatially and temporally is key in developing reliable kinetic models, as well as in validating proposed reaction mechanisms. In this work, two techniques, IR-thermography and spatially-resolved capillary inlet mass spectrometry (SpaciMS), were used to measure temperature and gas-phase concentrations. Specifically, they were applied to monitor the axial distribution of temperature and concentration profiles during propylene oxidation over a Pt/Al2O3 monolith-supported catalyst. Also, the effect of thermally aging the catalyst on the temperature and concentration patterns observed was investigated. During temperature programmed oxidation experiments, the data show that conversion of propylene began at the outlet, and a reaction front generated at the rear of the monolith traveled upstream, as a moving reaction zone, thereby creating a temperature wave pattern since the reaction is exothermic. The conversion was always complete downstream of this reaction zone at any point along the catalyst. When the reactor was cooled, the conversion of propylene started to drop, accompanied by a similar temperature wave pattern that traveled in the opposite direction (from upstream to downstream) and was attributed to a phenomenon known as wrong-way behavior. Finally, thermally aging the catalyst led to a slower and more localized moving hot zone.

碩士
國立交通大學
環境工程系所
104
Selective catalytic reduction of nitrogen oxides with NH3 is one of the most effective methods for removal of NOx from flue gases. In the SCR studies, TiO2 is developed as a superior support that exhibts high reactivity; however, it has no plasticity to extrude monolith applying on the field. Bentonite (clays) appears to have a relevant role as an inorganic binder and support. However, previous report showed that unmodified clays did not have great NO removal. Therefore, the aim of this research is to combine bentonite and TiO2 as bi-support, and then the catalysts were prepared by co-precipitation method. The NO conversion efficiencies of pellets and monolithic catalysts are discussed. To find out the best ratio of bi-supports, catalysts with high loading on the monolith and sucessful extruded monoliths were tested. The results show that bentonite-TiO2 catalysts had higher NO conversions than literature data which used unmodified Bentonite as support of SCR catalysts. The catalyst loading test on the monolithic showed that MnFe/TiO2 had low viscosity and less loading amount. However, bentonite:TiO2 ratios of 1:1, 1:2 and 1:3 have high viscosity and the highest loading amounts. In addition, MnFe/Bentonite:TiO¬2=1:3 could approach high NO conversion by only one time washcoat.

Η Ηλεκτροχημική Ενίσχυση της Κατάλυσης (ή φαινόμενο NEMCA) είναι ένα φαινόμενο όπου εφαρμογή μικρών ρευμάτων ή δυναμικών (±2 V) μπορεί να τροποποιήσει την ενεργότητα καταλυτών υποστηριγμένων σε ιοντικούς ή μικτούς ιοντικούς-ηλεκτρονικούς αγωγούς, να επηρεάσει την εκλεκτικότητα σε επιθυμητή κατεύθυνση και να μεταβάλλει τις ηλεκτρονικές και συνεπώς τις καταλυτικές ιδιότητες με τρόπο ελεγχόμενο, αντιστρεπτό και σε κάποιο βαθμό προβλέψιμο. Στην παρούσα διατριβή μελετήθηκε η επίδραση του πάχους του καταλυτικού υμενίου στο μέγεθος της ηλεκτροχημικής ενίσχυσης, χρησιμοποιώντας την αντίδραση της οξείδωσης του C2H4 σε πορώδη υμένια Pt πάχους μεταξύ 0.2 και 1.4 μm, εναποτεθειμένα με τη μέθοδο επάλειψης οργανομεταλλικής πάστας, σε στερεό ηλεκτρολύτη YSZ, έναν αγωγό ιόντων Ο2-. Βρέθηκε πως η αύξηση του πάχους των υμενίων που χρησιμοποιούνται στις μελέτες ηλεκτροχημικής ενίσχυσης, προκαλεί μείωση στο λόγο προσαύξησης του ρυθμού, ρ, συμπεριφορά που βρίσκεται σε καλή συμφωνία με τις αναλυτικές προβλέψεις του μαθηματικού μοντέλου που περιγράφει την επιφανειακή διάχυση-αντίδραση των προωθητικών ειδών. Με βάση τις επιτυχείς μελέτες ηλεκτροχημικής ενίσχυσης που έχουν πραγματοποιηθεί σε λεπτά (40 nm), εναποτεθειμένα με τη μέθοδο της ιοντοβολής (sputtering) καταλυτικά υμένια, έγινε επέκταση της μελέτης της επίδρασης του πάχους σε τόσο λεπτά υμένια. Συγκεκριμένα, εξετάσθηκε η καταλυτική και η ηλεκτροχημικά ενισχυμένη συμπεριφορά πολύ λεπτών (30-90 nm) καταλυτικών υμενίων εναποτεθειμένων με τη μέθοδο του sputtering, τη μέθοδο Pulsed Laser Deposition και την τεχνική εναπόθεσης με ατμό (vapor deposition). Τιμές του λόγου προσαύξησης του ρυθμού, ρ, έως και 440 και τιμές φαρανταϊκής απόδοσης, Λ, έως και 1000 παρατηρήθηκαν για τα υμένια που εναποτέθηκαν με τη μέθοδο του sputtering. Η διασπορά μετάλλου στα υμένια αυτά είναι έως και 20%, συγκρίσιμη δηλαδή με αυτή των εμπορικών υποστηριγμένων καταλυτών. Τέλος, παρουσιάζεται η λειτουργία ενός πρόσφατα ανεπτυγμένου μονολιθικού ηλεκτροχημικά ενισχυόμενου αντιδραστήρα (MEPR), χρησιμοποιώντας την περιβαλλοντικού ενδιαφέροντος αντίδραση της αναγωγής του ΝΟ από αιθυλένιο παρουσία Ο2. Χρησιμοποιώντας καταλυτικά στοιχεία τύπου Pt-Rh(1:1)/YSZ/Au, παρουσία 10% Ο2 και σε ογκομετρικές παροχές έως και 1000 cc/min, ο αντιδραστήρας λειτούργησε επιδεικνύοντας τιμές φαρανταϊκής απόδοσης που ξεπερνούν τη μονάδα και επιτυγχάνοντας 50% και 44% προσαύξηση στους ρυθμούς μετατροπής του καυσίμου και του ΝΟ αντίστοιχα. Αυτή η μελέτη είναι η πρώτη που επιδεικνύει ηλεκτροχημική ενίσχυση της αντίδρασης αναγωγής του NO σε τόσο υψηλές τιμές μερικής πίεσης οξυγόνου (10% O2), που είναι αντιπροσωπευτικές για εξατμίσεις μηχανών πτωχού καυσίμου και μηχανών Diesel. Ο MEPR αποδεσμεύει το φαινόμενο NEMCA από την έως σήμερα χρήση του στην καθαρά εργαστηριακή κλίμακα και δείχνει πολλά υποσχόμενος για την πρακτική εφαρμογή του φαινομένου.
The effect of Electrochemical Promotion of Catalysis (EPOC or NEMCA effect) is a phenomenon where application of small currents or potentials (±2 V) alters the activity and selectivity of catalysts supported on ionic or mixed ionic-electronic conductors and modifies the electronic and thus catalytic properties in a controllable, reversible and to some extent predictable manner. The effect of catalyst film thickness on the magnitude of electrochemical promotion (ρ and Λ values) has not been studied experimentally so far but a mathematical model has been developed, accounting for surface diffusion and reaction of the promoting species, which predicts a strong variation of ρ and Λ with catalyst film thickness L. In the present thesis is examined for the first time experimentally the effect of catalyst film thickness on the magnitude of the EPOC, using porous Pt catalyst-electrodes prepared from Engelhard Pt paste with thicknesses in the range 0.2 to 1.4 μm. It was found that increasing the thickness of porous catalyst films used in electrochemical promotion studies causes a decrease in the rate enhancement ratio, ρ, due to the gradual axial decrease from the three-phase-boundaries to the top of the film of the surface concentration of the promoting backspillover O2- species which diffuse and react on the porous catalyst surface. Increasing film thickness causes a moderate increase in the Faradaic efficiency, Λ, which can be predicted by the parameter 2Fro/I0. The ρ and Λ behaviour is in good agreement with the analytical model prediction and provides additional support for the O2- promoter reaction-diffusion model and for the sacrificial promoter mechanism of electrochemical promotion. Most electrochemical promotion studies have been carried out so far with thick (0.1 μm to 5 μm) porous metal catalyst films with a roughness factor of the order of 500 and small (typically less than 0.1%) metal dispersion, deposited on solid electrolytes using a variety of deposition techniques. Very recently, electropromotion studies have been extended to thin (40 nm) sputter coated porous metal catalysts with metal dispersion of the order of 10 to 30%. The effect of thickness with such thin (30 to 90 nm) sputtered Pt catalyst-electrodes on the magnitude of electrochemical promotion is discussed, as well as the effect of the catalyst deposition method (Sputtering, Pulsed Laser Deposition and Vapor Deposition) using the model reaction of ethylene oxidation. Rate enhancement ratio, ρ, values up to 440 and Λ values up to 1000 where obtained for the sputtered films, in agreement with the sacrificial promoter and diffusion-reaction models of EPOC which predict increase in ρ value with thinner films. An environmental interest reaction, the reduction of NO by ethylene in the presence of excess oxygen, was investigated in a recently developed MEPR. In this novel dismantlable monolithic-type electrochemically promoted catalytic reactor, thin (~40 nm) porous catalyst films are sputter-deposited on thin (0.25 mm) parallel solid electrolyte plates supported in the grooves of a ceramic monolithic holder and serve as electropromoted catalyst elements. Using Pt-Rh(1:1)/YSZ/Au-type catalyst elements, the 8-plate reactor operated with apparent Faradaic efficiency exceeding unity achieving significant and reversible enhancement in the rates of C2H4 and NO consumption in presence of up to 10% O2 in the feed at gas flow rates up to 1000 cc/min. The Pt-Rh co-sputtered films exhibited very good performance in terms of stability and selectivity for N2 formation, i.e. practically 100% under all reaction conditions. The reactor, which is a hybrid between a monolithic catalytic reactor and a flat-plate solid oxide fuel cell, permits easy practical utilization of the electrochemical promotion of catalysis.

An improved steady-state method combining experiment and mathematical modelling has been developed to characterize the scalable convective heat transfer coefficient, hvol [W*m^(-3)*K^(-1)], of uncoated and catalyst-support coated aluminium foam monoliths. The values of hvol were recovered by parameter fitting its model values to experimental temperature data for steady-state air-cooled monoliths under a known heating flux. The model was built with experimentally recovered values of the monolith’s thermal conductivity and fluid permeability along with known values for other physical parameters. The volumetric heat transfer coefficients of 10, 20 and 40 pore-per-inch uncoated aluminium foams were determined to range between 2,700 and 20,000 W*m^(-3)*K^(-1) at channel Reynolds numbers between 85 and 1,700. The presence of a 76 micron thick anodized layer of catalyst support on monolith foams effected a small but significant reduction in the value of hvol. Coating with an anodized layer also reduced the permeabilities of the monoliths to air flow by 4-20%. Knowledge of the scalable parameter, hvol, was used to model a steady-state non-isothermal, non-isobaric heat-coupled methanol reformer. The model shows that changes to the convective transfer coefficient due to coating the monolith with catalyst support may have significant consequences for the thermal profile of the model reactor and for the product yield.
Thesis (Master, Chemical Engineering) -- Queen's University, 2011-12-12 20:11:18.046

Η ηλεκτροχημική ενίσχυση της κατάλυσης (EPOC ή αλλιώς μη-φαρανταϊκή τροποποίηση της καταλυτικής ενεργότητας, φαινόμενο NEMCA) είναι ένα φαινόμενο όπου εφαρμογή μικρών ρευμάτων ή δυναμικών (±2V) σε ένα καταλύτη που είναι υποστηριγμένος σε ένα ηλεκτρολύτη, ιοντικό ή μικτό ιοντικό-ηλεκτρονικό αγωγό, μπορεί να επιφέρει τροποποιήσεις στην καταλυτική ενεργότητα αλλά και εκλεκτικότητα, με τρόπο ελεγχόμενο, αντιστρεπτό και έως ένα βαθμό προβλέψιμο. Η ηλεκτροχημική ενίσχυση έχει βρεθεί, με χρήση διαφόρων τεχνικών, ότι πηγάζει από την ηλεκτροχημικά ελεγχόμενη παροχή ενισχυτικών ιοντικών ειδών από το φορέα-ηλεκτρολύτη στα καταλυτικά σωματίδια. Στο πρώτο κεφάλαιο της παρούσας διατριβής γίνεται μια εκτεταμένη αναφορά στους στερεούς ηλεκτρολύτες, στις ιδιότητες τους και τους τομείς στους οποίους χρησιμοποιούνται με ιδιαίτερη σημασία στη σταθεροποιημένη με οξείδιο του υττρίου ζιρκονία (YSZ), που αποτελεί ένα πολύ συχνά χρησιμοποιούμενο αγωγό ιόντων οξυγόνου. Επίσης, εισάγονται οι έννοιες της μετανάστευσης (spillover) και της αντίστροφης μετανάστευσης (backspillover), οι οποίες χρησιμοποιούνται στην ερμηνεία και την κατανόηση του φαινομένου της ηλεκτροχημικής ενίσχυσης και των αλληλεπιδράσεων μετάλλου-φορέα (MSI). Στο δεύτερο κεφάλαιο γίνεται εισαγωγή στις γενικές αρχές του φαινομένου της ηλεκτροχημικής ενίσχυσης όπου παρουσιάζονται μερικά παραδείγματα εφαρμογής του και γίνεται ανασκόπηση όλων των εργασιών που έχουν εμφανιστεί στη βιβλιογραφία και αφορούν στο συγκεκριμένο φαινόμενο. Συζητείται, επίσης, η μελέτη του φαινομένου με χρήση διαφόρων πειραματικών τεχνικών, όπως ηλεκτροκινητικών πειραμάτων δυναμικής απόκρισης, μετρήσεων έργου εξόδου, κυκλικής βολταμμετρίας, XPS, TPD και STM, καθώς και θεωρητικών μελετών, με σκοπό την κατανόηση της αρχής του φαινομένου σε ατομικό επίπεδο καθώς και την επίλυση σημαντικών προβλημάτων που αφορούν στην ετερογενή κατάλυση. Με βάση τα αποτελέσματα από τις ανωτέρω μελέτες, παρουσιάζεται το μαθηματικό μοντέλο που έχει αναπτυχθεί και εξηγεί τα παρατηρούμενα φαινόμενα σε μοριακό επίπεδο καθώς και οι πρόσφατα εδραιωμένοι κανόνες που το διέπουν. Στο τρίτο κεφάλαιο παρουσιάζεται η αξιοποίηση του φαινομένου της ηλεκτροχημικής ενίσχυσης στην αντιμετώπιση ενός εκ των δυσκολότερων και προκλητικότερων προβλημάτων της ετερογενούς κατάλυσης που είναι η αναγωγή του μονοξειδίου του αζώτου (ΝΟ) από αιθυλένιο παρουσία υψηλής περίσσειας (10%) οξυγόνου. Στην μελέτη χρησιμοποιήθηκε ένας πρόσφατα ανεπτυγμένος και βελτιωμένος για την παρούσα διατριβή, μονολιθικός ηλεκτροχημικά ενισχυόμενος αντιδραστήρας (monolithic electrochemically promoted reactor, MEPR) εξοπλισμένος με 22 ηλεκτροχημικά καταλυτικά στοιχεία του τύπου Rh/YSZ/Pt με μικρό πάχος ηλεκτροδίων (~40 nm). Βρέθηκε, δε, ότι η βέλτιστη λειτουργία επιτυγχάνεται σε χαμηλές θερμοκρασίες (220-240οC) με σημαντική ηλεκτροχημική ενίσχυση ακόμα και κάτω από τις ανωτέρω ισχυρά οξειδωτικές συνθήκες (λόγος αέρα-καυσίμου=16.7, περίσσεια οξυγόνου=9.43). Σε αυτό το στενό θερμοκρασιακό εύρος η εκλεκτικότητα προς Ν2 που επετεύχθη από τα Rh/YSZ/Pt ηλεκτροκαταλυτικά στοιχεία, είναι περίπου 100% ενώ η παραγωγή των ανεπιθύμητων CO, ΝΟ2, Ν2Ο ήταν σχεδόν μη-ανιχνεύσιμη. Στο τέταρτο κεφάλαιο μελετάται η χρήση λεπτών καταλυτικών ηλεκτροδίων Pt σκελετικής δομής (Pt-skeletal/YSZ/Au) στην έκταση του φαινομένου της ηλεκτροχημικής ενίσχυσης, χρησιμοποιώντας την πρότυπη αντίδραση οξείδωσης αιθυλενίου, στον μονολιθικό ηλεκτροχημικά ενισχυόμενο αντιδραστήρα. Βρέθηκε ότι και τέτοιου τύπου ηλεκτρόδια – καταλυτικά υμένια είναι ιδιαίτερα καταλυτικά ενεργά και είναι δυνατό να ενισχυθούν ηλεκτροχημικά σε μεγάλο βαθμό. Επίσης, ο αντιδραστήρας λειτούργησε επιτυχώς και παρατηρήθηκε ηλεκτροχημική ενίσχυση, υπό υψηλές ογκομετρικές παροχές (25 l/min), με ταχύτητες χώρου αντιδραστήρα που είναι κοντά σε αυτές που λειτουργούν οι βιομηχανικοί αντιδραστήρες (12000 h-1). Στο πέμπτο κεφάλαιο παρουσιάζεται η ηλεκτροχημική ενίσχυση της αντίδρασης υδρογόνωσης του CO2 με στόχο την παραγωγή μεθανίου χρησιμοποιώντας ηλεκτροχημικά στοιχεία του τύπου Rh/YSZ/Pt. Βρέθηκε ότι η αντίδραση μπορεί να ενισχυθεί σε μεγάλο βαθμό και επιπλέον να τροποποιηθεί και η εκλεκτικότητά της σε CΗ4 που είναι και το επιθυμητό προϊόν. Στο έκτο κεφάλαιο παρουσιάζεται η μελέτη της αντίδραση οξείδωσης του SO2 προς SO3, μιας πολύ σημαντικής αντίδρασης από βιομηχανική (παραγωγή H2SO4) αλλά περιβαλλοντική άποψη, με χρήση του φαινομένου της ηλεκτροχημικής ενίσχυσης, σε λεπτά (~40 nm) ηλεκτροχημικά στοιχεία του τύπου Pt/YSZ/Au. Βρέθηκε πως ηλεκτροχημική ενίσχυση μπορεί να επιτευχθεί ακόμα και σε πολύ υψηλές ογκομετρικές παροχές (30 l/min), όπου αντιστοιχούν σε ταχύτητες χώρου αντιδραστήρα (14000 h-1) πολύ κοντά σε αυτές που λειτουργούν οι βιομηχανικοί αντιδραστήρες και να επιτευχθούν σχετικά υψηλές μετατροπές SO2.
Electrochemical Promotion of Catalysis (EPOC or Non-Faradaic Electrochemical Modification of Catalytic Activity, NEMCA effect) is a phenomenon where the application of small currents or potentials (±2V) alters the activity and selectivity of catalysts supported on ionic or mixed ionic-electronic conductors and modifies the catalytic activity and selectivity, in a controllable, reversible and to some extend predictable manner. As shown by numerous surface science techniques, including STM, electrochemical promotion is due to electrochemically controlled migration (backspillover) of promoting or poisoning ionic species (Oδ- in the case of YSZ) between the ionic or mixed ionic-electronic conductor and the gas exposed catalytic surface. The utilization of electrochemical promotion of catalysis, in order to tackle one of the most difficult and challenging problems of heterogeneous catalysis, which is the NO reduction under high excess oxygen (10%), has been performed. This gas mixture is a typical mixture in a lean-burn engine (or Diesel engine) exhaust. In this study, a recently developed and improved monolithic electrochemically promoted reactor (MEPR) has been used, equipped with 22 thin (~40 nm catalyst-electrode thickness) electrochemical catalytic elements Rh/YSZ/Pt type. It was found that there is an optimum operation temperature of the reactor, in the range from 220oC to 240oC, where the maximum electropromotion effect occurs, even under these extremely oxidizing conditions (air/fuel ratio = 16.7 and oxygen excess = 9.43%). In this narrow temperature window the selectivity to N2 was almost 100% since the production of the undesired N2O and NO2 was almost undetectable. Also, the use of thin catalytic Pt electrodes with skeletal structure (Ptskeletal/ YSZ/Au) was examined in the MEPR for the model reaction of C2H4 oxidation. It was found that such skeletal structure electrodes are catalytically active and can be electropromoted even under high gas flow rates (25 l/min) or high space velocity (HSV~12000 h-1), close to those that the industrial reactors operate. The electrochemical promotion of the CO2 hydrogenation reaction was also examined, towards methane production using Rh/YSZ/Pt type electrochemical catalytic elements. It was found that the reaction rates can be enhanced and similarly the selectivity to CH4 which found to increase upon polarization. Finally, the effect of electrochemical promotion was examined in the study of the SO2 oxidation to SO3 reaction, which is a very important reaction by industrial (H2SO4 production) and environmental point of interest. The monolithic reactor was equipped with 5 or 22 thin (~40 nm) Pt/YSZ/Au type electrocatalytic elements. It was found that electrochemical promotion can be obtained by positive polarization even under high hourly space velocities (14000 h-1), close to those that the industrial reactors operate, with relatively high SO2 conversions.