Energy efficient purification of hydrogen is an important technological challenge with broad applications in the chemical, petrochemical, metallurgical, pharmaceutical, textile and energy industries. Palladium-alloy membranes are particularly suited to this problem due to their high hydrogen permeability, thermal stability, and virtually infinite selectivity. In current systems hydrogen flux is observed to be inversely proportional to membrane thickness which is indicative of the interstitial diffusion mechanism of hydrogen permeation. This observation, along with the high cost of palladium, has motivated continuous efforts to decrease membrane thickness. Theoretical modeling of membrane performance predicts that as membrane thickness continues to decrease, eventually the permeation rate will no longer be limited by diffusion through the bulk Pd but will become limited by desorption from the permeate surface. If it exists, this is a vital transition to pinpoint due to the fact that below this thickness membrane operating conditions will have a drastically different effect on hydrogen permeation behavior and no additional performance enhancements will result from further decreasing thickness. A handful of experimental results in the open literature contradict these modeling predictions. A new model is developed in this work to explain these contradictions by considering the non-ideal behavior of hydrogen solution into metals which has been neglected in previous models. Additionally, it has been demonstrated that hydrogen permeation through bulk Pd depends on membrane microstructure, making deposition conditions and post-deposition thermal treatment important issues for repeatable performance. The interplay of these issues on the performance of ultra-thin, Pd-Ag alloy hydrogen separating membranes is experimentally investigated. It is demonstrated that the hydrogen permeation behavior of sub-micrometer thick Pd-Ag alloy membranes exhibits diffusion-limited behavior in the context of the new model. The microstructure evolution during annealing is characterized and a correlation is drawn with the observed transient hydrogen permeation behavior during initial testing of a new membrane. In addition, two distinct failure modes of the microfabricated membranes are observed and the implications for future Pd-based membrane research are discussed.

Direct methanol fuel cells (DMFC) are being investigated as a portable energy conversion device for military and commercial applications. DMFCs offer the potential to efficiently extract electricity from a dense liquid fuel. However, improvements in materials properties and lowering the cost of the electrocatalysts used in a DMFC are necessary for commercialization of the technology. The cathode electrocatalyst is a critical issue in DMFC because the state-of-the-art catalyst, platinum, is very expensive and rare, and its performance is diminished by methanol that crosses over from the anode to the cathode through the Nafion membrane. This thesis investigates the addition of platinum to a palladium-cobalt nanoalloy electrocatalyst supported on carbon black in order to improve catalyst activity for the oxygen reduction reaction (ORR) and catalyst stability against dissolution in acidic environment without significantly reducing the methanol-tolerance of the catalyst. Platinum was added to the palladium-cobalt nanoalloy catalyst using two synthesis methods. In the first method, platinum was directly alloyed with palladium and cobalt using a polyol reduction method, followed by heat treatment in a reducing atmosphere to form catalysts with 11 and 22 atom % platinum. In the second method, platinum was added to a palladium-cobalt alloy by galvanic displacement reaction to form catalysts with 10 and 22 atom % platinum. The palladium cobalt alloy was synthesized using a polyol method, followed by heat treatment in a reducing atmosphere to alloy the nanoparticles before the Pt displacement. It was found that both methods significantly improve catalyst activity and stability, with the displaced catalysts showing a higher activity than the corresponding alloy catalyst. However the alloy catalysts showed similar resistance to dissolution as the displaced catalysts, and the alloyed catalysts were more tolerant to methanol. The displaced catalyst with 22 atom % platinum (8 wt. % Pt overall) performed similar to a 20 wt. % commercial platinum catalyst in both RDE and single cell DMFC tests. The 10 and 22 atom % Pt displaced catalysts and 22 atom % Pt alloyed all showed higher Pt mass specific activities than a commercial Pt catalyst. / text

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Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

The analysis of metals is now a major application area for ICP-AES, however, the technique suffers from both spectral and non-spectral interferences. This thesis details the application of univariate and multivariate calibration methods for the prediction of Pt, Pd, and Rh in acid-digested and of Au, Ag and Pd in fusion-digested autocatalyst samples. Of all the univariate calibration methods investigated matrix matching proved the most accurate method with relative root mean square errors (RRMSEs) for Pt, Pd and Rh of 2.4, 3.7, and 2.4 % for a series of synihelic lest solutions, and 12.0, 2.4, and 8.0 % for autocatalyst samples. In comparison, the multivariate calibration method (PLSl) yielded average relative errors for Pt, Pd, and RJi of 5.8, 3.0, and 3.5 % in the test solutions, and 32.0, 7.5, and 75.0 % in the autocatalyst samples. A variable selection procedure has been developed enabling multivariate models to be built using large parts of the atomic emission spectrum. The first stage identified and removed wavelengths whose PLS regression coefficients were equal to zero. The second stage ranked the remaining wavelengths according to their PLS regression coefficient and estimated standard error ratio. The algorithms were applied to the emission spectra for the determination of Pt, Pd and Rh in a synthetic matrix. For independent test samples variable selection gave RRMSEs of 5.3, 2.5 and 1.7 % for Pt, Pd and Rh respectively compared with 8.3, 7.0 and 3.1 % when using integrated atomic emission lines. Variable selection was then applied for the prediction of Au, Ag and Pd in independent test fusion digests. This resulted in RRMSEs of 74.2, 8.8 and 12.2 % for Au, Ag and Pd respectively which were comparable to those obtained using a more traditional univariate calibration approach. A preliminary study has shown that calibration drift can be corrected using Piecewise Direct Standardisation (PDS). The application of PDS to synthetic test samples analysed 10 days apart resulted in RRMSEs of 4.14, 3.03 and 1.88%, compared to 73.04, 44.39 and 28.06 % without correction, for Pt, Pd, and Rh respectively.

This work focuses on understanding the heterogeneous/homogeneous nature of the catalytic species for a variety of immobilized metal precatalysts used for C-C coupling reactions. These precatalysts include: (i) tethered organometallic palladium pincer complexes, (ii) an encapsulated small molecule palladium complex in a polymer matrix, (iii) mercapto-modified mesoporous silica metalated with palladium acetate, and (iv) amino-functionalized mesoporous silicas metalated with Ni(II). As part of this investigation, the use of metal scavengers as selective poisons of homogeneous catalysis is introduced and investigated as a test for distinguishing heterogeneous from homogeneous catalysis. The premise of this test is that insoluble materials functionalized with metal binding sites can be used to selectively remove soluble metal, but will not interfere with catalysis from immobilized metal. In this way the test can definitely distinguish between surface and solution catalysis of immobilized metal precatalysts. This work investigates three different C-C coupling reactions catalyzed by the immobilized metal precatalysts mentioned above. These reactions include the Heck, Suzuki, and Kumada reactions. In all cases it is found that catalysis is solely from leached metal. Three different metal scavenging materials are presented as selective poisons that can be used to determine solution vs. surface catalysis. These selective poisons include poly(vinylpyridine), QuadrapureTM TU, and thiol-functionalized mesoporous silica. The results are contrasted against the current understanding of this field of research and subtleties of tests for distinguishing homogeneous from heterogeneous catalysis are presented and discussed.

Thesis (Ph. D.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographical references.

Les nanotubes de carbone possèdent d’excellentes propriétés mécaniques, thermiques, électriques…, ce qui en fait un candidat de choix pour le développement de nouveaux matériaux pour de nombreuses applications. Cependant, leur mauvaise dispersion dans les solvants et les matrices reste encore aujourd’hui le principal problème pour l’obtention de matériaux composites homogènes. Cette thèse présente une nouvelle voie de fonctionnalisation des nanotubes de carbone réalisée en milieux fluides supercritiques. La fonctionnalisation organique proposée via une oxydation de surface des NTC présente de nombreux avantages par rapport aux techniques conventionnelles. La fonctionnalisation inorganique des NTC par les nanoparticules de palladium et d’argent a servi de modèle pour mieux appréhender le dépôt de nanoparticules de cuivre et déboucher ainsi à la réalisation de matériaux composites cuivre/NTC. / Carbon nanotubes possess excellent mechanical, thermal, electrical properties and so on. Therefore they are excellent candidates for the development of new materials potentially used in numerous applications. However, obtaining homogenous composite materials requires, as well in solvents or in matrices, a good dispersion of carbon nanotubes which is still a problem. This work presents a new way to functionalize carbon nanotubes using supercritical fluids. The proposed organic functionalization, a surface oxidation of carbon nanotubes, turns out to be favourable compared with conventional techniques. Inorganic functionnalization was first performed with palladium and silver nanoparticles depositions. Information provided by these previous depositions was used to carry out depositions of copper nanoparticles leading to the formation of copper/CNT composites.

La détection de l'hydrogène est une priorité environnementale. De nombreux capteurs à hydrogène ont déjà été développés, mais aucun d’eux ne répond aux exigences de l'industrie. Les capteurs à fibres optiques, électriquement isolés, sont d’excellents candidats pour fonctionner dans des environnements explosifs. Notre objectif est de développer un capteur à fibres optiques intrinsèque par Résonance de Plasmon de Surface pour la détection d’hydrogène. Dans cette thèse, nous étudions deux designs de capteurs à hydrogène. Le premier, basé sur la modulation d'amplitude, se compose d'une couche mince de Pd déposé sur le cœur de la fibre multimode, après avoir enlevé la gaine optique. Dans le second, basé sur la modulation de longueur d'onde, nous remplaçons la couche de Pd par un empilement de couches (Au / SiO 2 / Pd). Dans cette thèse, nous démontrons que les capteurs plasmoniques peuvent être une solution pour développer des capteurs à hydrogène fiables et rapides. Enfin, nous étudions des alliages de Mg comme matériaux sensibles à l’hydrogène afin d’optimiser la plage de détection des capteurs à hydrogène. / Hydrogen detection is an environmental priority. Numerous hydrogen sensors have been developed, but none of them meet the industry requirements. Optical fiber sensors, electrically isolated, are excellent candidates for operating in explosive environments. Our goal is to develop an intrinsic optical fiber sensor based on Surface Plasmon Resonance. In this thesis, we study two optical fiber hydrogen sensors. The first sensor, based on amplitude modulation, consists of a thin Pd layer deposited on the multimode fiber core, after removing the optical cladding. The second design, based on wavelength modulation, consists of replacing the single Pd layer by a Au/ SiO2/ Pd multilayer stack. We demonstrate in this thesis that plasmonic sensors may be a solution to develop fast and reliable fiber hydrogen sensors. Finally, we study Mg alloys as hydrogen sensitive material in order to improve the detection range of hydrogen sensors.