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<p> Recent investigations by H. G. Thode, J. Macnamara and C. Collins have shown that the S^32/S^34 ratio in natural sulfur-containing compounds varies by as much as five percent. These wide-spread variations suggest that fractionation of the sulfur isotopes occurs in natural processes due to differences in the chemical properties of isotopic molecules. In order to determine the magnitude of the effects that could be expected, partition function ratios for isotopic molecules containing sulfur and equilibrium constants for many isotopic exchange reactions involving sulfur have been calculated by methods of statistical mechanics. The results of these calculations are discussed. </p> / Thesis / Master of Science (MSc)

Ce projet est dédié à la recherche industrielle pour le développement de systèmes catalytiques innovants tels que le contrôle des émissions de véhicules. L'Europe connait actuellement une forte dépendance au niveau de l'importation de certains éléments utilisés comme support de catalyseur (oxyde de Cerium), nous souhaitons nous concentrer sur des éléments plus facilement disponibles tels que Ca, Fe, Mn, Sr, Cu... tout en essayant de garder le mécanisme catalytique bien connu de l'oxyde de cerium. Pour ce faire, nous avons sélectionné des conducteurs en oxygène de la famille des brownmillerites comme matériaux supports. Ceux ci présente des lacunes en oxygènes ayant un impact bénéfique sur leur activité catalytique pour les réactions d'oxydations. Il est aussi prévu de regarder les interactions entre métaux nobles et support conducteurs en oxygène pour une application de dépollution des gaz. Les réactions modèles étudiées au début de ce projet seront l'oxydation du CO ainsi que le stockage et la réduction des NOx. Les brownmillerites peuvent être vues comme des oxydes de type pérovskite avec un défaut en oxygène. Les brownmillerites ont une structure anisotropique avec un enchainement de lacines d'oxygènes-1D apportant une augmentation de l'activité catalytique. Ces browmillerites sont bien connues pour présenter une mobilité de l'oxygène à basse température. La présence de défauts tels que des liaisons anti-phase peut significativement diminuer la diffusion de l'oxygène. CaFeO2.5 riche en défauts, connu pour être une phase stœchiométrique peut être oxyder dans de "douces" conditions en CaFeO3 alors que l'oxydation d'un CaFeO2.5 ordinaire requiert des conditions extrêmes (1100°C et plusieurs GPa de pression en oxygène). Ainsi, introduire un nombre élevé de défauts dans la structure cristalline semble être une manière prometteuse de transformer des phases stoechiométriques en réservoir à oxygène. Les matériaux obtenus alors ayant des capacité de stockage et d'amélioration des réactions d'oxydations à température très modérée. Le mécanisme mis en jeu est comparable à celui de la capacité de stockage en oxygène des cérines dopées et offre donc un vrai potentiel catalytique. Au cours de ce projet CaFeO2.5 sera premièrement étudié mais nous étendrons l'étude avec des dopages (Cu, Mn, W) et une autre composition sera aussi étudiée : SrFeO2.5; Concernant le support nous souhaitons obtenir : -une grande dispersion du métal noble dans la matrice -une grande mobilité de l'oxygène à température modérée -une grande surface spécifique Obtenir ces trois caractéristiques simultanément est actuellement un challenge pour les brownmillérites. Pour ce faire nous souhaitons étudier différentes voies de synthèse. Une grande partie du projet sera dédiée aux caractérisations des matériaux avec des analyses structurales et spectroscopiques incluant de l'échange isotopique pour l'étude de la mobilité en oxygène. Ces études permettront une meilleure compréhension des propriétés des matériaux en relation avec leur activité catalytique. Les matériaux les plus prometteurs à l'issue de cette étude seront synthétisés à l'échelle du pilote par un processus d'électro-fusion. / The present project is dedicated to industrial research for the development of innovative catalytic systems for air purification, such as those used for the control of road vehicle emission (three way converter, TWC). In the context of Europe’s dependency on imports of some critical elements currently used as catalyst support (e.g. cerium oxide), we focus on more available elements such as Ca, Fe, Mn, Sr, Cu… by keeping the well-understood mechanisms governing the catalytic activity of cerium oxide in mind. As such, we choose oxygen ion conductors of the Brownmillerite family as support material, because it has been reported that lattice oxygen atoms have a beneficial impact on the catalytic activity of oxidation reactions. Next to the pure support material, also the interaction of a noble metal with the oxygen ion conductive support for the efficient removal of gas phase pollutants will be studied. In terms of catalytic reactions, the oxidation of CO, and the storage and reduction of NOx will be the primary metrics. In this project, oxygen ion conductors of the Brownmillerite family are chosen as support material. Brownmillerites can be regarded as oxygen-deficient perovskite type oxides. The Brownmillerite type structure is anisotropic with 1D-oxygen vacancy channels providing a catalytically enhanced surface/interface structure. Brownmillerites are known to reveal oxygen ion mobility down to ambient temperature. The presence of extended defects as anti-phase boundaries can significantly decrease the activation energy for oxygen diffusion. Defect-rich CaFeO2.5, which is traditionally known to be a stoichiometric line-phase, can be oxidized under mild conditions to CaFeO3, while the oxidation of ordinary CaFeO2.5 usually requires extreme reaction conditions, i.e. 1100°C and several GPa oxygen partial pressure. Thus, introducing a high concentration of defects seems to be a promising concept to transform even traditionally known stoichiometric line-phases to become a kind of oxygen sponge and behave as oxygen storage/buffer compound at very moderate temperatures. This mechanism is thus comparable to the oxygen storage capacity of doped cerium oxide, and offers a true potential for application in catalysis. Consequently, the Brownmillerite CaFeO2.5 will be a first candidate to study due to its known oxygen ion conductivity properties, however, also doping with other elements (e.g. Cu, Mn, W) and other compositions (e.g. SrFeO2.5) will be investigated. For the support material, we will attempt to achieve (i)- a high degree of dispersion of the noble metal into the matrix, (ii)- a high oxygen mobility at moderate temperatures (e.g. by introducing defects) and (iii)- a high surface area, which we anticipate to be key aspects for achieving high catalytic activity. To date, it is still a challenge to achieve these goals simultaneously for Brownmillerites. As a result, in this project, several synthesis routes are foreseen. More straightforward synthesis routes, such as citrate- EDTA gel methods and spray pyrolysis, will be investigated alongside with more advanced synthetic approaches such and hard-templating routes. This multitude of possibilities allows for an easy adaption of a synthesis route to the material under study. A major part of the project will be dedicated to the detailed characterization of the materials involving large scale facilities for structure analysis and spectroscopy (in-situ studies), including oxygen isotope exchange reactions to trace the oxygen ion mobility. These studies will allow for a detailed understanding of the materials properties in relation to its catalytic activity. The most promising materials will be synthesized on a pilot-scale using electrofusion. This technique is well-established by the industrial partner and is extremely suitable for the synthesis of reduced powders, such as CaFeO2.5.

Mass, solute (chloride), isotope (deuterium) and thermal balances were completed at Perry Lakes, two semi-permanent 'water table' lakes near Perth, Western Australia. All balance components except groundwater discharge/recharge were measured independently. These difficult to measure groundwater components of lake-aquifer interaction were estimated by integrating mass, solute and chloride data in sequential 4 day balances spanning two years. Before urbanisation, such wetlands functioned predominantly as flow-through lakes. Now, large winter storm water inputs (and summer artificial level maintenance pumped locally from groundwater) dominate. In East Lake these inputs together comprise 42% of the annual water budget; groundwater discharge is reduced to just 2%. Even under flow-through conditions, these 'non natural' inputs are so large East Lake always tends towards a recharge state and commonly becomes a local groundwater mound. Flow-through is established in both lakes over winter. Initially each lake functions separately however as winter progresses shared capture and release zones are established. Maintenance of lake levels in early summer forces East Lake back to recharge status. Sediment heat flux (Qse) is significant in these very shallow lakes. Over summer Qse was negative, with a net movement of heat from the water into the sediments which act as a seasonal heat sink. In winter Qse was positive and stored summer heat was returned to the water column. This flux at times exceeded 40 W m-2. Evaporation was determined independently by floating pan, leaving Qse as the thermal balance residual. Ignoring Qse, annual evaporation determined by thermal balance was over estimated by 7%. Over and under estimates of individual 12 day balance period evaporation exceeded 50%. Monthly Class A (Perth airport) pan coefficients varied from 0.54 (January) to 0.86 (September). Ten empirical equations for evaporation were calibrated and compared with the East Lake floating pan. Best performer was the Makkink which tracked the floating pan closely throughout all seasons. Poorest were the Penman, DeBruin-Keijman, Priestly-Taylor and Brutsaert-Stricker which grossly over estimated late winter evaporation. Transpiration from Typha orientalis, estimated using hydrograph techniques was 43% of open water evaporation in summer and 28% annually. Temperature controlled evaporation pans (tracking lake temperature) experimentally determined the local deuterium content of lake evaporate ƒÔE, required for isotopic balances. Techniques employing pans evaporated to dryness and pans evaporated at constant volume were run in tandem continuously for two years. This study singularly integrates mass, solute and isotope balances thereby allowing groundwater components to be accurately quantified. The isotope balances are unique, being the only such balances incorporating experimentally derived local deuterium values of lake evaporate. This study represents the only thermal balance, the only accurate determination of pan-lake coefficients and the first calibration of commonly used empirical evaporation equations for Swan Coastal Plain wetlands. Groundwater levels in the western suburbs of Perth have declined over 40 years and a disproportionate larger decline now seriously threatens Perry Lakes. Modelling suggests regional groundwater extraction exceeds recharge. Wetland managers can no longer maintain East Lake via local groundwater extraction. Artificial recharge using imported surface and waste water are possible future management options.

Αντικείμενο της παρούσας διατριβής ήταν η μελέτη των δομικών και καταλυτικών ιδιοτήτων καταλυτών ΜοΟ3 υποστηριγμένων σε οξειδικούς φορείς. Η χρήση της φασματοσκοπικής μεθόδου Raman υπό ελεγχόμενες in situ συνθήκες επέτρεψε το χαρακτηρισμό των καταλυτών κάτω από ένα εύρος συνθηκών που μελετήθηκαν. Η εφαρμογή της μεθοδολογίας Operando Raman-GC οδήγησε σε συμπεράσματα αναφορικά με δομικές αλλαγές και δεδομένα καταλυτικής αποτελεσματικότητας ενώ συνδυασμός των δονητικών φασματοσκοπιών Raman και FTIR με πειράματα ισοτοπικής εναλλαγής 18Ο/16Ο χρησιμοποιήθηκε για εκτενέστερη διερεύνηση της μοριακής δομής των καταλυτών. Ειδικότερα εξετάσθηκε μια σειρά καταλυτών ΜοΟ3/ΤiO2 με in situ φασματοσκοπία Raman κάτω από οξειδωτικές και αναγωγικές συνθήκες, καθώς επίσης και κάτω από συνθήκες αντίδρασης οξειδωτικής αφυδρογόνωσης του αιθανίου. Η μοριακή δομή των επιφανειακών ειδών μολυβδενίου βρέθηκε να σχετίζεται άμεσα με το σχηματισμό κυρίως απομονωμένων ειδών Μο, για χαμηλές και υψηλές φορτίσεις κοντά στη μονοστρωματική κάλυψη, ενώ για φορτίσεις που υπερβαίνουν το μονόστρωμα παρατηρήθηκε ο σχηματισμός κρυσταλλικού ΜοΟ3. Η αποτίμηση της καταλυτικής ενεργότητας κατέδειξε πως καταλύτες με πολύ καλή διασπορά του ΜοΟ3 πάνω στην επιφάνεια παρουσιάζουν τα βέλτιστα αποτελέσματα. Επιπροσθέτως, εξετάζεται η επίδραση του φορέα (ZrO2, Al2O3, TiO2 και SiO2) στη δομή και στην καταλυτική συμπεριφορά μονοστρωματικών υποστηριγμένων καταλυτών MoO3 για την αντίδραση της οξειδωτικής αφυδρογόνωσης του αιθανίου με την φασματοσκοπία Raman. Μελετήθηκε η επίδραση της φόρτισης, της θερμοκρασίας, της σύστασης της αέριας τροφοδοσίας και του χρόνου παραμονής των αντιδρώντων πάνω στα χαρακτηριστικά των φασμάτων Raman καθώς και στην καταλυτική ενεργότητα με στόχο την εξαγωγή σχέσεων δομής-ενεργότητας/εκλεκτικότητας υποστηριγμένων καταλυτών MoO3/MxOy (M=Zr, Al, Ti, Si) για την οξειδωτική αφυδρογόνωση του αιθανίου. Η επιλογή της φύσης του φορέα/υποστρώματος κρίθηκε ως σημαντικός παράγοντας που ελέγχει την αποτελεσματικότητα της λειτουργίας των καταλυτών για την ODH του αιθανίου. Τέλος, οι δονητικές φασματοσκοπίες Raman και FTIR κάτω από ελεγχόμενες in situ συνθήκες χρησιμοποιήθηκαν για τη διερεύνηση της μοριακής δομής των καταλυτικών συστημάτων MoO3/ZrO2, MoO3/Al2O3 και MoO3/TiO2. Η φασματοσκοπία Raman σε συνδυασμό με πειράματα ισοτοπικής εναλλαγής 18Ο/16Ο οδήγησε σε αξιόλογα συμπεράσματα αναφορικά με τη μοριακή δομή των διεσπαρμένων μολυβδενικών ειδών υπό το πρίσμα της διάκρισης μεταξύ mono-oxo και di-oxo δομών. Τα αποτελέσματα συνέκλιναν στην παρουσία mono-oxo μοριακών διαμορφώσεων για κάθε καταλυτικό σύστημα (MoO3/ZrO2, MoO3/Al2O3 και MoO3/TiO2), τόσο για χαμηλές όσο και για φορτίσεις κοντά στο μονόστρωμα. Η υποκατάσταση γειτονικών οξειδικών θέσεων των Μο=16Ο δεσμών βρέθηκε να συμβάλει στη σταδιακή μετατόπιση της κορυφής αυτών των δεσμών σε χαμηλότερες συχνότητες μέσω ενός φαινομένου που ονομάστηκε “δονητικό ισοτοπικό φαινόμενο υποκατάστασης 18Ο/16Ο επόμενων κοντινότερων γειτόνων” (Next – Nearest – Neighbor 18Ο/16Ο substitution vibrational isotope effect). / The present work focuses on the study of structural and catalytic properties of the dispersed phase of supported MoO3 catalysts. In situ Raman spectroscopy has been used to characterize the supported catalysts and provide fundamental information about the configuration and the molecular structure under various controlled gas atmospheres and operating temperatures. A strategy involving the combined use of in situ Raman and in situ FTIR vibrational spectroscopies and the combined use of in situ Raman spectroscopy and 18O2/16O2 isotopic exchange experiments has been applied to investigate the molecular structure of the molybdena dispersed phase. A series of supported molybdenum oxide catalysts supported on TiO2(anatase) has been extensively examined by means of in situ and operando Raman spectroscopy under oxidizing, reducing and ODH of ethane conditions. The molecular structure of the surface MoOx species has been assigned to the formation of isolated units, primarily as O=Mo(–O–Ti)3 with a characteristic Mo=O sretching frequency observed at 994 cm-1 both at low as well as at high coverage below monolayer (~6 Mo/nm2). A weak and broad band at ~925 cm-1 due to Mo–O– Mo functionalities becomes visible with increasing loading, indicating a low presence of associated (polymeric) molybdates with increasing loading on TiO2. When exceeding monolayer coverage, the Raman spectra revealed the formation of bulk crystalline MoO3 on the TiO2 support. Detailed catalytic studies of the supported molybdena catalysts on titania showed that the monolayer catalyst (15MoTi) provide better catalytic results. Additionally, the structural and catalytic properties of monolayer MoO3 catalysts supported on ZrO2, Al2O3, TiO2 and SiO2 were studied for the oxidative dehydrogenation (ODH) of ethane by in situ and operando Raman spectroscopy. The molecular structure of the dispersed surface species evolves from isolated monomolybdates (MoO4 and MoO5) to associated (MoOx)n units in polymolybdate chains, depending on the support. The nature of the oxide support material and of the Mo–O–support bond has a significant influence on the catalytic behavior of the molybdena catalysts with monolayer coverage while, the dependence of reactivity on the support follows the order ZrO2 > Al2O3 > TiO2 > SiO2. The vibrational properties of molybdena catalysts supported on titania, zirconia and alumina were studied by means of in situ vibrational (Raman and FTIR) spectroscopies and 18O/16O isotopic exchange experiments combined with in situ Raman spectra at 450 °C. The aim of this work was the discrimination between mono-oxo and di-oxo configuration for the deposited molybdena phase at low as well as at high coverage near monolayer. The vibrational isotope effects and the combined interpretation of the observed Raman fundamental, IR overtone, as well as calculated zero-order band wavenumbers and characteristics suggest a mono-oxo configuration for the deposited molybdena phase at low as well as at higher coverage, irrespective of the extent of association (polymerization). A “nextnearest- neighbor 18O/16O substitution” vibrational effect is observed, resulting in small red shifts (2–7 cm−1) of the Mo=16O Raman band wavenumber. This effect is found to be strongly related to the nature of the support, regarding the extent of the shift, and assigned to the different reducibilities of the various support materials.