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The catalycal oxidation of hydrogen sulphide in presence of small amounts of hexan has been investigated over a Titania catalyst. H2S is converted into sulphur. Nevertheless the catalyst undergoes a deactivation through coke formation. In order to explain the coke profile in the inner of the catalyst's pellet, the influence of the internal heat and mass transfers has been considered using a pore network. / Die katalytische Oxydation von Schwefelwasserstoff auf einem TiO2-Anatase-Katalysator wird in Anwesenheit von n-Hexan durchgeführt. Schwefel wird gebildet. Der Katalysator unterliegt jedoch eine schnelle Deaktivierung durch Russbildung, die anhand eines Porennetzwerksmodells simuliert werden wird. Sowohl Stoff- als auch Wärmetransport werden berücksichtigt.

Στην παρούσα εργασία, η αποθήκευση υδρογόνου σε νανοσωλήνες άνθρακα εξετάστηκε με τη βοήθεια δύο πειραματικών τεχνικών: ρόφηση υδρογόνου και θερμοπρογραμματιζόμενη εκρόφηση υδρογόνου. Τα δείγματα που εξετάστηκαν για αποθήκευση υδρογόνου περιελάμβαναν MWCNTs, thinMWCNTs και SWCNTs. Τα πειράματα ρόφησης υδρογόνου πραγματοποιήθηκαν σε θερμοκρασία 298 Κ και σε εύρος πίεσης 0-1000 Torr και τα αποτελέσματα που προέκυψαν είναι, 0.12-0.17 wt.%, 0.22 wt.% καιι 0.30-0.36 wt.% αντίστοιχα. Τα αποτελέσματα που προέκυψαν από τους υπολογισμούς της ενέργειας ενεργοποίησης εκρόφησης (~20 kJ/mol) των TPD πειραμάτων οδήγησαν στο συμπέρασμα ότι η αποθηκευτική ικανότητα Η2 των CNTs δεν είναι αποτέλεσμα μόνο φυσικής ρόφησης, αλλά και φαινόμενα χημικής ρόφησης λαμβάνουν χώρα και ότι η διαθέσιμη προς ρόφηση Η2 επιφάνεια των CNTs είναι ομοιόμορφη, αφού η ποσότητα Η2 που ροφήθηκε στους CNTs στους 298 Κ, εκροφήθηκε από αυτούς στην ίδια θερμοκρασία. Η ενίσχυση της ικανότητας ρόφησης Η2 ενός υλικού, λαμβάνει χώρα μέσω του φαινομένου spillover. Pt εναποτέθηκε στους CNTs μέσω υγρού εμποτισμού ή μέσω ανάμιξης στη συσκευή υπερήχων του αιωρήματος των CNTs στο διάλυμα της πρόδρομης ένωσης. Στους CNTs που εξετάστηκαν, η παρουσία Pt στην επιφάνεια τους, σχεδόν διπλασίασε την αποθηκευτική τους ικανότητα σε Η2. Οι εμπλουτισμένοι με αλκάλια CNTs εμφανίζουν μεγαλύτερα ποσοστά αποθήκευσης Η2 από τους μη εμπλουτισμένους. Η συμπεριφορά αυτή έχει αποδοθεί στη δημιουργία δίπολου πάνω στο μόριο του Η2, λόγω της ύπαρξης σημειακών φορτίων στα αλκάλια. Το μέγιστο ποσοστό αποθήκευσης που επιτεύχθηκε στην παρούσα εργασία είναι το 0.7 wt.%, στους 298 Κ, για το υλικό 0.5% Pt/ Li(5%)-SWCNTs-85%. Στα κελιά καυσίμου ΡΕΜ, το μεγάλο κόστος λόγω της παρουσίας του καταλύτη Pt στα ηλεκτρόδια τους, αποτελεί τον κυριότερο περιορισμό για την εμπορευματοποίηση τους. Ως εκ τούτου, στόχος είναι η αποδοτικότερη χρήση του καταλύτη Pt με ταυτόχρονη μείωση της ποσότητας του. Στην παρούσα εργασία μελετήθηκαν, μέσω ηλεκτροχημικών πειραμάτων, οι καταλύτες Pt/SWCNTs, Pt/MWCNTs και Pt/Vulcan-XC72. Η εναπόθεση της Pt έλαβε χώρα με τις προαναφερθείσες μεθόδους, και τα αποτελέσματα των πειραμάτων έδειξαν ότι τόσο η μέθοδος εναπόθεσης Pt, όσο και το είδος των CNTs, επηρεάζουν τα ηλεκτροχημικά χαρακτηριστικά των ηλεκτροδίων. Μέγιστη παραγόμενη ισχύς της τάξης των 0.21 W/cm2, επιτεύχθηκε με τους καταλύτες Pt/SWCNTs με χρήση τους ως ηλεκτρόδιων ανόδου. / In this study, hydrogen storage on carbon nanotubes was studied via two main methods: hydrogen adsorption and temperature programmed desorption. CNTs (multi-walled, thin multi-walled and single walled) of variable purity were tested for their hydrogen adsorption capacity at 298 in the pressure range of 0 to 1000 Torr. Maximum adsorption capacity per unit mass of the solid was observed over SWCNTs (0.30-0.36 wt.%), followed by thinMWCNTs (0.22 wt.%) and MWCNTs (0.12-0.17 wt.%). Temperature programmed desorption revealed that the adsorption sites on the CNTs surface are relatively uniform, due to the fact that the quantity of hydrogen desorbed is very close to the quantity of hydrogen adsorbed. The calculated values of desorption activation energy (~20 kJ/mol) revealed that adsorption on CNTs is not purely physical in nature but it also involves weak chemisorption bonds. One potential way to enhance hydrogen storage on carbon nanotubes is spillover effect. Pt was deposited on CNTs via wet impregnation (method A) or mixture of the suspension of carbon nanotubes in the solution of the precursor under sonication (method B). Both, hydrogen adsorption experiments at 298 K and temperature programmed desorption measurements revealed that hydrogen storage capacity observed over CNTs was almost double. Experimental and theoretical researches have shown that alkali doped CNTs presented higher values of hydrogen storage capacity, compared to non alkali doped CNTs. This behavior has been attributed to the creation of bipolar forces in the hydrogen molecule, due to the charge transfer in alkalis. The highest storage capacity presented in this work was 0.7 wt.%, for Li doped CNTs when Pt was deposited on them via method B. The use of CNTs as platinum support for proton exchange membrane fuel cells has been investigated as a way to reduce the cost of fuel cells through an increased utilization of platinum. This work presents results with Pt catalysts supported on CNTs and also on commonly used carbon powder, Vulcan XC-72, prepared via methods mentioned above. The results indicate electrochemical characteristics which depend strongly on the nature of the support and the Pt deposition method. Power density of 0.21 W/cm2 at 80 0C was achieved with Pt/SWCNTs fed with H2 and the activity of the anodes followed the sequence: Pt/SWCNTs > Pt/MWCNTs > Pt/Vulcan XC-72.

The catalycal oxidation of hydrogen sulphide in presence of small amounts of hexan has been investigated over a Titania catalyst. H2S is converted into sulphur. Nevertheless the catalyst undergoes a deactivation through coke formation. In order to explain the coke profile in the inner of the catalyst's pellet, the influence of the internal heat and mass transfers has been considered using a pore network. / Die katalytische Oxydation von Schwefelwasserstoff auf einem TiO2-Anatase-Katalysator wird in Anwesenheit von n-Hexan durchgeführt. Schwefel wird gebildet. Der Katalysator unterliegt jedoch eine schnelle Deaktivierung durch Russbildung, die anhand eines Porennetzwerksmodells simuliert werden wird. Sowohl Stoff- als auch Wärmetransport werden berücksichtigt.

Styrene production by a (FlDAB)PdII(TFA)(η2-C2H4) complex was modeled using density functional theory (DFT). Benzene C-H activation by this complex was studied via five mechanisms: oxidative addition/reductive elimination, sigma-bond metathesis, concerted metalation deprotonation (CMD), CMD activation of ethylene, and benzene substitution of ethylene followed by CMD of the ligated benzene. Calculations provided evidence that conversion of benzene and ethylene to styrene was initiated by the fifth pathway, arylation via CMD of coordinated benzene, followed by ethylene insertion into the Ru-Ph bond, and then β-hydrogen elimination. Also, monomer (active species)/dimer equilibrium concentrations were analyzed. The results obtained from present study were compared with that of a recently reported RhI complex to help identify more suitable catalysts for the direct production of styrene from ethylene and benzene. Second, theoretical studies of heterobimetallic {Ag–Fe(CO)5}+ fragments were performed in conjunction with experiments. The computational models suggested that for this first example of a heterodinuclear, metal-only FeAg Lewis pair (MOLP) that Fe(CO)5 acts as a Lewis base and AgI as a Lewis acid. The ῡCO bands of the studied molecules showed a blue shift relative to those measured for free Fe(CO)5, which indicated a reduction in Fe→CO backbonding upon coordination to silver(I). Electrostatic interaction is predicted via DFT as the dominant mode of Fe—Ag bonding augmented by a modest amount of charge transfer between Ag+ and Fe(CO)5. Third, computational analyses of hypothetical transition metal-terminal boride [MB(PNPR)] complexes were reported. DFT, natural orbital analysis (NBO), and multiconfiguration self-consistent field (MCSCF) calculations were employed to investigate the structure and bonding of terminal boride complexes, in particular the extent of metal dπ - boron pπ bonding. Comparison of metal-boride, -borylene and –boryl bond lengths confirms the presence of metal-boron π bonds, albeit the modest shortening (~ 3%) of the metal-boron bond suggests that the π-bonding is weak. Their instabilities, as measured by free energies of H2 addition to make the corresponding boryl complexes, indicate terminal boride complexes to be thermodynamically weak. It is concluded that for the boride complexes studied, covering a range of 4d and 5d metals, that the metal-boride bond consisted of a reasonably covalent σ and two very polarized π metal-boron bonds. High polarization of the boron to metal π-bonds indicated that a terminal boride is an acceptor or Z type ligand. Finally, anti-Markovnikov addition of water to olefins has been a long-standing goal in catalysis. The [Rh(COD)(DPEphos)]+ complex was found as a general and regioselective group 9 catalyst for intermolecular hydroamination of alkenes. The reaction mechanism was adapted for intermolecular hydration of alkenes catalyzed by a [Rh(DPEphos)]+ catalyst and studied by DFT calculations. Olefin hydration pathways were analyzed for anti-Markovnikov and Markovnikov regioselectivity. On the basis of the DFT results, the operating mechanism can be summarized as follows: styrene activation through nucleophilic attack by OHδ− of water to alkene with simultaneous Hδ+ transfer to the Rh; this is then followed by formation of primary alcohol via reductive elimination. The competitive formation of phenylethane was studied via a β-elimination pathway followed by hydrogenation. The origin of the regioselectivity (Markovnikov vs anti-Markovnikov) was analyzed by means of studying the molecular orbitals, plus natural atomic charges, and shown to be primarily orbital-driven rather than charge-driven.