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Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 142-144) Also available in print.

C3H6 oxidation over a Pt/Al2O3 catalyst with or without NOx present was investigated. In particular, its reaction mechanism was studied using diffuse reflectance infrared spectroscopy (DRIFTS), a reactor system designed for monolith-supported catalysts and a micro-reactor system designed for powder catalysts referred to as CATLAB. These experiments reveal that C3H6 oxidation is inhibited by the presence of NO, NO oxidation is inhibited by the presence of CeH6, and that adsorbed NOx can react with gas phase C3H6. DRIFTS and CATLAB results confirm the reaction between C3H6 and nitrates, which are formed during NOx adsorption, with linear nitrites observed as reaction products. Therefore, a reaction route is proposed for C3H6 oxidation in the presence of NOx, namely, nitrates acting as oxidants. Using NO2 instead of NO, or using a high NOx/C3H6 ratio, which is beneficial for nitrate formation, favors this reaction pathway. Data also showed that Pt is required for this reaction, which suggests the nitrates in proximity to the Pt particles are affected/relevant. Reaction kinetics studies of C3H6 oxidation over Pt/Al2O3 and Pt/SiO2 catalysts were performed in CATLAB using a temperature-programmed oxidation method with different oxidants: O2, NO2 and nitrates. The reaction kinetics of these possible reactions were compared in order to determine which reaction is more important. NOx adsorption does not occur on the SiO2 surface so the reaction between C3H6 and NO2 could be isolated and the effect of nitrates could be observed as well when compared to the results from Pt/Al2O3. The Pt dispersions were determined using H2 chemisorption and were 1.3 and 1.6% for Pt/Al2O3 and Pt/SiO2, respectively. C3H6 oxidation starts at a lower temperature with O2 than with NO2 but the activation energy was lower with NO2. This gives indication that hydrocarbons must be activated first for NO2 to be favored in hydrocarbon oxidation. When the experiment was done with C3H6 and nitrates, the reaction did not occur until NOx started to desorb from the catalyst at higher temperatures, when nitrates become unstable and decompose. Therefore, O2 was added to the system and the reaction began at even lower temperature than with just C3H6 and O2. This proved that hydrocarbons need to be activated in order for surface nitrates to affect C3H6 oxidation and this reaction also resulted in a lower activation energy than with just C3H6 and O2. Nitrate consumption was also observed as less NOx desorbed from the catalyst at the later stage of the temperature ramp compared to the amount desorbed when the catalyst was not exposed to C3H6.

C3H6 oxidation over a Pt/Al2O3 catalyst with or without NOx present was investigated. In particular, its reaction mechanism was studied using diffuse reflectance infrared spectroscopy (DRIFTS), a reactor system designed for monolith-supported catalysts and a micro-reactor system designed for powder catalysts referred to as CATLAB. These experiments reveal that C3H6 oxidation is inhibited by the presence of NO, NO oxidation is inhibited by the presence of CeH6, and that adsorbed NOx can react with gas phase C3H6. DRIFTS and CATLAB results confirm the reaction between C3H6 and nitrates, which are formed during NOx adsorption, with linear nitrites observed as reaction products. Therefore, a reaction route is proposed for C3H6 oxidation in the presence of NOx, namely, nitrates acting as oxidants. Using NO2 instead of NO, or using a high NOx/C3H6 ratio, which is beneficial for nitrate formation, favors this reaction pathway. Data also showed that Pt is required for this reaction, which suggests the nitrates in proximity to the Pt particles are affected/relevant. Reaction kinetics studies of C3H6 oxidation over Pt/Al2O3 and Pt/SiO2 catalysts were performed in CATLAB using a temperature-programmed oxidation method with different oxidants: O2, NO2 and nitrates. The reaction kinetics of these possible reactions were compared in order to determine which reaction is more important. NOx adsorption does not occur on the SiO2 surface so the reaction between C3H6 and NO2 could be isolated and the effect of nitrates could be observed as well when compared to the results from Pt/Al2O3. The Pt dispersions were determined using H2 chemisorption and were 1.3 and 1.6% for Pt/Al2O3 and Pt/SiO2, respectively. C3H6 oxidation starts at a lower temperature with O2 than with NO2 but the activation energy was lower with NO2. This gives indication that hydrocarbons must be activated first for NO2 to be favored in hydrocarbon oxidation. When the experiment was done with C3H6 and nitrates, the reaction did not occur until NOx started to desorb from the catalyst at higher temperatures, when nitrates become unstable and decompose. Therefore, O2 was added to the system and the reaction began at even lower temperature than with just C3H6 and O2. This proved that hydrocarbons need to be activated in order for surface nitrates to affect C3H6 oxidation and this reaction also resulted in a lower activation energy than with just C3H6 and O2. Nitrate consumption was also observed as less NOx desorbed from the catalyst at the later stage of the temperature ramp compared to the amount desorbed when the catalyst was not exposed to C3H6.

Υπάρχει ένα συνεχές ενδιαφέρον για τη σύνθεση και το χαρακτηρισμό συμπλόκων των μετάλλων μετάπτωσης (μεταβατικών μετάλλων) με υποκαταστάτες βενζοτριαζολικού τύπου. Το ενδιαφέρον αυτό οφείλεται κυρίως στην αντιδιαβρωτική δραστικότητα του βενζοτριαζολίου (btaH) έναντι ορισμένων μετάλλων κυρίως του Cu και των κραμάτων του. Οι μοριακοί μηχανισμοί της παρεμπόδισης της διάβρωσης των μετάλλων από τα βενζοτριαζόλια δεν έχουν διερευνηθεί πλήρως. Στην παρούσα Διπλωματική Εργασία αναπτύσσεται ένα μοντέλο της παρεμπόδισης της διάβρωσης του Fe από το btaH με τη χρησιμοποίηση ιδεών της Χημείας Ένταξης (Συναρμογής). Παρασκευάσθηκαν τα σύμπλοκα [FeCl3(Mebta)2] (1), [FeCl3(btaH)2] (2), (Et3NH)[Fe14O9(OMe)9Cl9(bta)7(MeOH)2(H2O)2] (3), [FeCl3(5ClbtaH)2].2(5ClbtaH) (4), [FeCl3(5,6dimebtaH)2] (5), [FeBr3(btaH)2] (6), [Fe14O8(OH)(OMe)9Br9(bta)7(MeOH)2(H2O)2].2MeOH (7.2MeOH) και {(5ClbtaH)2H}[FeBr4] (8), όπου Mebta = 1- μεθυλοβενζοτριαζόλιο, 5ClbtaH = 5-χλωροβενζοτριαζόλιο και 5,6dimebtaH = 5,6-διμεθυλοβενζοτριαζόλιο. Τα σύμπλοκα χαρακτηρίσθηκαν με μικροαναλύσεις και φασματοσκοπία IR. Οι μοριακές και κρυσταλλικές δομές των ενώσεων προσδιορίσθηκαν με κρυσταλλογραφία ακτίνων Χ επί μονοκρυστάλλων. Τα σύμπλοκα 1, 2 και 4-6 είναι μονοπυρηνικά με πέντε μονοδοντικούς υποκαταστάτες (τρεις αλόγονο, δύο Ν-δότες). Το ιόν FeIII βρίσκεται σε ένα τριγωνικό διπυραμιδικό περιβάλλον ένταξης με τους τρεις αλόγονο υποκαταστάτες να ορίζουν το ισημερινό επίπεδο. Η ένωση 8 είναι ιοντική, περιλαμβάνοντας το πρωτότυπο κατιόν {(5ClbtaH)2H}+ και το τετραεδρικό ανιόν [FeBr4]-. Το πολυπυρηνικό ανιόν της πλειάδας 3 συγκρατείται μέσω έξι μ3-O2-, τριών μ4-O2-, εννέα μ2-OMe-, πέντε η1:η1:η1:μ3 bta- και δύο η1:η1:μ2 bta- υποκαταστατών. Η περιφερειακή ένταξη συμπληρώνεται από εννέα Cl-, δύο MeOH και δύο H2O με τους τρεις αυτούς υποκαταστάτες να είναι τερματικοί. Τα κέντρα FeIII υιοθετούν τρεις διαφορετικές γεωμετρίες ένταξης (οκταεδρική, τριγωνική διπυραμιδική, τετραεδρική). Τα δεκατέσσερα κέντρα FeIII ορίζουν μια εξαεπιστεγασμένη εξαγωνική διπυραμίδα. Το πολυπυρηνικό μόριο της ένωσης 7.2MeOH έχει παρόμοια δομή με αυτήν του ανιόντος του 3, με έναν μ3-O2- υποκαταστάτη του 3 να έχει αντικατασταθεί από έναν και μοναδικό μ3-OH- υποκαταστάτη στην 7.2MeOH. Οι δεκατετραπυρηνικές πλειάδες 3 και 7.2MeOH μπορούν να θεωρηθούν ως μοντέλα της παρεμπόδισης της διάβρωσης του Fe σε ουδέτερα pH, ενώ η κρυσταλλική δομή της ένωσης 8 δίνει μια ένδειξη σχετικά με το μοριακό μηχανισμό των αντιδιαβρωτικών ιδιοτήτων επιλεγμένων βενζοτριαζολίων έναντι του σιδήρου σε όξινα pH. Τα σύμπλοκα 2 και 4 αποτελούν αποτελεσματικούς ομογενείς καταλύτες σε αντιδράσεις οξείδωσης αλκανίων και αλκενίων με το “πράσινο” οξειδωτικό H2O2. Η παρούσα εργασία μπορεί επίσης να θεωρηθεί ως μια συνεισφορά στη χημεία ένταξης των βενζοτριαζολίων και στη χημεία των πλειάδων του FeIII. / There is continuing interest in the synthesis and characterization of transition metal complexes with benzotriazole ligands. This is primarily due to the anticorrosion activity of benzotriazole (btaH) towards certain metals, particularly Cu and its alloys. The molecular mechanisms for the corrosion inhibition of metals by benzotriazoles have not been completely elucidated. An inorganic chemistry model approach to the corrosion inhibition of Fe by btaH has been developed in the present Diploma Thesis. Complexes [FeCl3(Mebta)2] (1), [FeCl3(btaH)2] (2), (Et3NH)[Fe14O9(OMe)9Cl9(bta)7(MeOH)2(H2O)2] (3), [FeCl3(5ClbtaH)2].2(5ClbtaH) (4), [FeCl3(5,6dimebtaH)2] (5), [FeBr3(btaH)2] (6), [Fe14O8(OH)(OMe)9Br9(bta)7(MeOH)2(H2O)2].2MeOH (7.2MeOH) and {(5ClbtaH)2H}[FeBr4] (8), where Mebta = 1- methylbenzotriazole, 5ClbtaH = 5-chlorobenzotriazole and 5,6dimebtaH = 5,6-dimethylbenzotriazole, have been prepared. The complexes have been characterized using microanalyses and IR spectroscopy. The molecular and crystal structures of the compounds have been determined by single-crystal X-ray crystallography. Complexes 1, 2 and 4-6 are mononuclear with five monodentate ligands (three halogenido, two N-donors). The FeIII ion is in a trigonal bipyramidal coordination environment with the three halogenido ligands defining the equatorial plane. Compound 8 is ionic, containing the novel {(5ClbtaH)2H}+ cation and the tetrahedral [FeBr4]- ion. The cluster anion of 3 is held together by six κ3-O2-, three κ4-O2-, nine κ2-OMe-, five ε1:ε1:ε1:κ3 bta- and two ε1:ε1:κ2 bta- ligands. Peripheral ligation is completed by nine Cl-, two MeOH and two H2O terminal ligands. The FeIII centers adopt three different coordination geometries (octahedral, trigonal bipyramidal, tetrahedral). The 14 FeIII centers define a hexacapped hexagonal bipyramid. The cluster molecule of 7.2MeOH has a similar structure; one κ3-O2- of 3 has been replaced by a unique κ3-OH- in 7.2MeOH. The tetradecanuclear clusters 3 and 7.2MeOH may be considered as models for the corrosion inhibition of Fe by benzotriazoles at neutral pHs, while the crystal structure of 8 gives a clue for the molecular mechanism of the anticorrosion properties of selected benzotriazoles towards iron at acidic pHs. Complexes 2 and 4 are effective homogeneous catalysts for alkane and alkene oxidations with the eco-friendly oxidant H2O2. iv The present work can be also considered as a contribution in the coordination chemistry of benzotriazoles and in the cluster chemistry of FeIII.

Abstract The combustion of fuels in motor vehicles is one of the most significant causes of air emissions. The use of oxidation catalysts in exhaust gas emission treatment can reduce hydrocarbons (HCs) and carbon monoxide (CO) emissions by more than 90%. Fuels and engine lubricants contain impurities like sulphur (S) and phosphorus (P), which can have a significant effect on the activity and durability of oxidation catalysts. This thesis aims at increasing the current knowledge of the deactivation phenomena caused by sulphur and phosphorus in diesel and natural/bio gas oxidation catalysts. Accelerated laboratory scale sulphur, phosphorus and thermal treatments in gas-phase conditions were carried out for alumina (Al2O3) based platinum (Pt) and platinum-palladium (PtPd) metallic monolith diesel and natural gas oxidation catalysts. In addition, a vehicle-aged natural gas oxidation catalyst and an engine-bench-aged diesel oxidation catalyst were studied and used as a reference for the laboratory-scale-aged catalysts. BET-BJH, FESEM, TEM, XPS and DRIFT were used as characterization techniques to determine changes on the catalysts. The effect of accelerated deactivation treatments on the catalyst activity was determined using laboratory scale measurements in CO, HC and nitric oxide (NO) oxidation. Sulphur and phosphorus were found to cause morphological and chemical changes on the studied catalysts. Sulphur was found to be adsorbed vertically throughout the entire catalyst support from the catalyst surface to the metallic monolith, while phosphorus accumulated on the surface region of the precious metal containing catalysts. Both, sulphur and phosphorus, slightly increased the average size of the precious metal particles size and are adsorbed onto the alumina by chemical bonds. In addition, a partial transformation from PdO to Pd and a change in the shape of the precious metal particles due to phosphorus were detected. Due to the detected structural and chemical changes on the catalysts, sulphur and phosphorus treatments reduced the catalytic activity of the studied diesel and natural-gas-oxidation catalysts. Correspondence between real and simulated ageing was found and thus the used accelerated laboratory scale aging method can be stated to be a good tool to simulate sulphur and phosphorus exposure. / Tiivistelmä Moottoriajoneuvot ovat merkittäviä ilmapäästöjen aiheuttajia. Hapetuskatalyyttejä käyttämällä hiilimonoksidi- ja hiilivetypäästöistä pystytään poistamaan yli 90 %. Polttoaineet ja voiteluaineet sisältävät epäpuhtauksia kuten rikkiä ja fosforia, jotka voivat merkittävästi heikentää hapetuskatalyyttien aktiivisuutta ja kestävyyttä. Väitöskirjan tavoitteena on tuottaa uutta tietoa rikin ja fosforin aiheuttamasta diesel- ja maakaasukatalyyttien deaktivoitumisesta. Metalliseen monoliittiin tuettuja alumiinioksidipohjaisia platina- ja palladiumkatalyytteja ikäytetiin tekemällä niille rikki-, fosfori- ja lämpökäsittelyjä. Maantieikäytettyä maakaasuhapetuskatalyyttiä ja moottoripenkki-ikäytettyä dieselhapetuskatalyyttiä käytettiin laboratorioikäytettyjen katalyyttien referensseinä. Ikäytyskäsittelyjen aiheuttamat muutokset analysoitiin BET-BJH-, FESEM-, TEM-, XPS- ja DRIFT-menetelmillä. Käsittelyjen vaikutus katalyyttien hiilimonoksidin, hiilivetyjen ja typenoksidien hapetusaktiivisuuteen tutkittiin laboratoriomittakaavan aktiivisuuslaitteella. Rikki ja fosfori aiheuttivat rakenteellisia ja kemiallisia muutoksia tutkittuihin katalyytteihin. Rikki adsorboitui koko tukiaineeseen (tukiaineen pinnalta pohjalle), kun taas fosfori adsorboitui vain pinnan alueelle. Sekä rikki että fosfori kasvattivat jalometallipartikkeleiden kokoa sekä muodostivat alumiinioksidin kanssa yhdisteitä. Lisäksi fosforikäsittelyjen havaittiin osittain pelkistävän PdO:n Pd:ksi ja muuttavan jalometallipartikkelien muotoa. Havaitut rikin ja fosforin aiheuttamat rakenteelliset sekä kemialliset muutokset laskivat diesel- ja maakaasukatalyyttien hapetusaktiivisuutta. Laboratorioikäytyksillä havaittiin olevan hyvä korrelaatio todellisissa olosuhteissa tehtyjen ikäytysten kanssa ja tästä syystä työssä käytetyn laboratoriomittakaavan ikäytysmenetelmän voidaan todeta olevan hyvä työkalu simuloimaan rikin ja fosforin aiheuttamaa deaktivoitumista.

Les normes plus restrictives visent à réduire les émissions de polluants, en particulier le CO2, favorisant l'usage des biocarburants. Cependant, le biodiesel contient des éléments inorganiques (Na, K, Ca et P) qui réduisent la durabilité des systèmes de post-traitement. Dans ce travail sont évalués les performances des catalyseurs d'oxydation diesel (DOCs, catalyseur de référence PtPd/CeZrO2/La-Al2O3). Les résultats de caractérisation ont montré l’influence de ces impuretés sur les propriétés physico-chimiques et catalytiques. Bien que la structure cristalline du catalyseur de référence ne change pas après l'incorporation des impuretés, la surface spécifique diminue. La capacité redox a diminué lorsque les impuretés Na, K et Ca sont présents du à leur faible électronégativité, ce qui augmente l'interaction avec l'oxygène. Cette interaction semble être responsable de l’augmentation de la vitesse de réaction de C3H6. Les résultats NO-TPD ont montré que la forte basicité ces impuretés entraînait une plus forte adsorption du NO. Par DRIFT il a été aussi montré que l’adsorption des intermédiaires du NO, associée au champ électrostatique créé par ces cations, empêche l'oxydation de NO. L'adsorption de CO a été favorisée, améliorant la conversion du CO. La formation de phosphate de cérium observée pourrait stabiliser l'état d'oxydation de Ce3+ (vérifié par XPS), en diminuant l'oxydation de NO due au blocage des sites catalytiques. Néanmoins, les co-oxydations de CO et de C3H6 ont été améliorées en évitant l'auto-empoisonnement. Après vieillissement hydrothermal, l'effet des impuretés a été masqué par le frittage de Pt/Pd, ce qui diminue les performances catalytiques / The more restrictive regulations to reduce pollutants emissions, especially CO2, promote the use of biofuels. However, biodiesel contains inorganic elements (Na, K, Ca and P) that reduce the durability of the after-treatment catalysts. This work aims to evaluate the performance of Diesel Oxidation Catalysts (DOCs, PtPd/CeZrO2/La-Al2O3 reference catalyst). The characterization results have shown that the above-mentioned impurities affect the physico-chemical, redox, surface and catalytic properties. Although the catalyst crystalline structure of reference catalyst did not change after impurities incorporation, the specific surface area decreased. The redox ability was also decreased when Na, K and Ca impurities are present due to their low electronegativity, which increased the oxygen interaction. This high interaction seems to be responsible of the enhanced C3H6 reaction rate. NO-TPD results evidenced that the high basicity of Na, K and Ca impurities resulted in an increase of NO adsorption strength. Accordingly, DRIFT results showed the presence of NO intermediates adsorption associated to the electrostatic field created by these cations, hindering NO oxidation. CO adsorption was also promoted, enhancing CO reaction rate. The formation of cerium phosphate was also observed, which could stabilize the Ce3+ oxidation state (checked by XPS), decreasing NO oxidation due to the blockage of catalytic sites. Nevertheless, CO and C3H6 co-oxidations were enhanced by avoiding self-poisoning. After catalyst hydrothermal aging, the effect of impurities was masked by the sintering of Pt/Pd active sites, which decreases the DOC catalytic performances

<p dir="ltr">Insights from research into the natural photosynthetic processes are applied to inform the rational design of inorganic catalysts. The study of these synthetic systems – artificial photosynthesis – will lead towards the development of a device able to absorb light, convert and store the energy in the form of chemical bonds. The water-splitting reaction, a bottleneck of the photosynthetic process, is a key barrier to overcome in this endeavor. Thus, the focused study of water-oxidation catalysts able to facilitate this difficult reaction is performed, in order to develop a green-energy solution in the form of an artificial photosynthesis system.</p>