Removal of polynuclear aromatics from diesel fuel has become a focus of intense research due to the stringent environmental legislation associated with clean fuels. In this work, selective ring opening of model compound decalin over the set of catalysts comprising of 1) Ir-Pt supported on mesoporous Zr-MCM-41, large and medium pore zeolites like HY and H-Beta and 2) Ni-Mo/carbide on HY, H-Beta, Al-SBA-15, ¥ã- alumina and silica alumina were studied. All the catalysts were extensively characterized by BET surface area measurement, CO-chemisorption, XRD, FTIR, TPR and TPD of ammonia. Ring opening of decalin was studied on these catalysts in a trickle-bed reactor in a temperature range of 200- 400 ¡ÆC, pressure range of 2-7 MPa and LHSV of 1 to 3 h- 1. 31.7 and 65.0 wt.% of RO yield and selectivity were observed on Ir-Pt/HY catalyst at 220 ¡ÆC, whereas 34.0 and 40.0 wt.% of ring opening yield and selectivity were observed on Ni-Mo carbide/HY catalyst at 240 ¡ÆC. From the model compound studies, Ir-Pt/HY, Ni-Mo carbide/HY and Ni-Mo carbide/H-Beta were selected for study of hydrotreated light gas oil in a trickle bed reactor. Ni-Mo carbide/HY performed better over other catalysts and increased the cetane index of hydrotreated light gas oil by 12 units at 325 ¡ÆC. A first order kinetic model was fitted for the hydrotreated light gas oil study. 89, 111 and 42 KJ/gmol of activation energies was observed for dearomatization, aromatization and naphthenes cracking steps, respectively. The thermodynamic equilibrium calculations reveal that the selectivity of ring opening products of decalin can be maximized by favoring the formation of unsaturated compounds at higher operating temperatures. Energetics of dealkylation and ring opening reactions of naphthenes in gas phase and on the surface of Br©ªnsted acid sites were calculated using quantum chemical simulations. In iv gas phase, ratio of Arrhenius activation energies for forward and reverse reactions of RO and dealkylation reactions are 1.92 and 1.82 respectively. Deakylation on different level clusters revealed that surface reaction is the rate controlling.

Removal of polynuclear aromatics from diesel fuel has become a focus of intense research due to the stringent environmental legislation associated with clean fuels. In this work, selective ring opening of model compound decalin over the set of catalysts comprising of 1) Ir-Pt supported on mesoporous Zr-MCM-41, large and medium pore zeolites like HY and H-Beta and 2) Ni-Mo/carbide on HY, H-Beta, Al-SBA-15, ¥ã- alumina and silica alumina were studied. All the catalysts were extensively characterized by BET surface area measurement, CO-chemisorption, XRD, FTIR, TPR and TPD of ammonia. Ring opening of decalin was studied on these catalysts in a trickle-bed reactor in a temperature range of 200- 400 ¡ÆC, pressure range of 2-7 MPa and LHSV of 1 to 3 h- 1. 31.7 and 65.0 wt.% of RO yield and selectivity were observed on Ir-Pt/HY catalyst at 220 ¡ÆC, whereas 34.0 and 40.0 wt.% of ring opening yield and selectivity were observed on Ni-Mo carbide/HY catalyst at 240 ¡ÆC. From the model compound studies, Ir-Pt/HY, Ni-Mo carbide/HY and Ni-Mo carbide/H-Beta were selected for study of hydrotreated light gas oil in a trickle bed reactor. Ni-Mo carbide/HY performed better over other catalysts and increased the cetane index of hydrotreated light gas oil by 12 units at 325 ¡ÆC. A first order kinetic model was fitted for the hydrotreated light gas oil study. 89, 111 and 42 KJ/gmol of activation energies was observed for dearomatization, aromatization and naphthenes cracking steps, respectively. The thermodynamic equilibrium calculations reveal that the selectivity of ring opening products of decalin can be maximized by favoring the formation of unsaturated compounds at higher operating temperatures. Energetics of dealkylation and ring opening reactions of naphthenes in gas phase and on the surface of Br©ªnsted acid sites were calculated using quantum chemical simulations. In iv gas phase, ratio of Arrhenius activation energies for forward and reverse reactions of RO and dealkylation reactions are 1.92 and 1.82 respectively. Deakylation on different level clusters revealed that surface reaction is the rate controlling.

Στην παρούσα μελέτη διερευνάται η αρχή του φαινομένου της ηλεκτροχημικής ενίσχυσης με την τεχνική της ηλεκτρονικής μικροσκοπίας σήραγγος (STM) και με την τεχνική Kelvin probe. Συγκεκριμένα, με το STM εξετάστηκε το σύστημα Pt(111)/YSZ υπό συνθήκες περιβάλλοντος προκειμένου να διερευνηθούν σε ατομική κλίμακα οι μεταβολές που υφίσταται η επιφάνεια του μονοκρυστάλλου της Pt μετά από ηλεκτροχημική παροχή ιόντων οξυγόνου στην επιφάνειά της. Βρέθηκε ότι το ηλεκτροχημικά παρεχόμενο οξυγόνο από το στερεό ηλεκτρολύτη στην επιφάνεια της Pt(111) δημιουργεί τη δομή Pt(111)-(12x12)-O. Με την τεχνική Kelvin probe μελετήθηκε το έργο εξόδου ηλεκτροδίων σε υδατικά διαλύματα και εν συνεχεία διερευνήθηκε η αρχή του απόλυτου δυναμικού των ηλεκτροδίων στην υγρή ηλεκτροχημεία. Τα αποτελέσματα επιβεβαιώνουν για πρώτη φορά την ισχύ της εξίσωσης: eUWR= ΦW – ΦR στην υγρή ηλεκτροχημεία και τονίζουν ότι το έργο εξόδου των αναδυόμενων ηλεκτροδίων, διαιρούμενο από το μοναδιαίο φορτίο του ηλεκτρονίου e, μπορεί να οριστεί ως το απόλυτο δυναμικό. Μελετήθηκε επίσης η αναγωγή των οξειδίων του αζώτου από C3H6 και από CO παρουσία οξυγόνου σε διεσπαρμένους καταλύτες ροδίου (Rh) και πλατίνας (Pt). Βρέθηκε ότι η αντίδραση αναγωγής του ΝΟ εξαρτάται από το είδος του φορέα και του μετάλλου. Τα αποτελέσματα συγκρινόμενα με αντίστοιχα πειράματα ηλεκτροχημικής ενίσχυσης, ΗΕ, έδειξαν τη βασική ομοιότητα του μηχανισμού της ΗΕ και των αλληλεπιδράσεων μετάλλου-φορέα, που συνίστανται στην διάχυση (backspillover) ιόντων Ο2- από το φορέα στο μέταλλο και την επακόλουθη αλλαγή της ισχύος των χημειοροφητικών δεσμών των αντιδρώντων. Επίσης μελετήθηκε η συμπεριφορά ζεόλιθου Cu-ZSM-5 στην αναγωγή του ΝΟ από προπυλένιο όπου βρέθηκε ότι ο συγκεκριμένος καταλύτης είναι ιδιαίτερα εκλεκτικός σε Ν2 υπό έντονα οξειδωτικές συνθήκες. / Scanning tunneling microscopy (STM) was used to investigate the surface of Pt single crystal catalyst surfaces interfaced with O2- conducting catalyst supports under conditions simulating electrochemical promotion and metal-support interactions. In both cases STM has clearly shown the reversible migration on the catalyst surface of promoting O2- species which are entirely distinct from normally chemisorbed oxygen originating from the gas phase. These observations provide useful information for the mechanism of electrochemical promotion and metal-support interactions, reveal the existence and fast migration of O2-, a most effective anionic promoter, on metal surfaces and underline its role in inducing the phenomena of electrochemical promotion and of metal-support interactions. In the second part of my thesis a two Kelvin probe setup is used for the first time in aqueous electrochemistry, to measure in situ and simultaneously the work functions, ΦW, ΦC and ΦR, of emersed working, counter and reference electrodes, respectively. The results confirm, for the first time, the validity of equation eUWR= ΦW – ΦR in aqueous electrochemistry and underline that the work function of emersed electrodes, divided by the unit charge e, can be used as the absolute potential. Additionally, in the last part of this thesis, it was studied NOx reduction by C3H6 and CO in the presence of oxygen on Rh and Pt dispersed catalysts. It was found that NO reduction depends on the support, but also on the type of the impregnating metal. The obtained results showed the similarity of electrochemical promotion and of metal-support interactions, when compared with corresponding NEMCA experiments. Finally, an ion-exchanged zeolite, Cu-ZSM-5, was used for NO reduction by propylene. It was found that the used zeolite was highly selective to dinitrogen production in high excess of oxygen.

Made available in DSpace on 2016-06-02T19:55:27Z (GMT). No. of bitstreams: 1 3046.pdf: 22010317 bytes, checksum: 740eb3cb48c20a2e8fee311c2c3dd513 (MD5) Previous issue date: 2010-06-15 / Universidade Federal de Sao Carlos / Pt catalysts supported on CeO2-La2O3-Al2O3, with different mixed oxide compositions, and CeO2-ZrO2-Al2O3, prepared using three different routes, were synthesized by sol gel technique. The samples were characterized using thermal analysis, N2 adsorption, X-ray diffraction, diffusive reflectance spectroscopy, Fourier transform infrared spectroscopy of CO adsorption and high resolution transmission electronic microscopy. The Pt dispersion was determined from the data of cyclohexane dehydrogenation rate. In situ temperature programmed reduction and Xray absorption near edge structure using redox treatments were performed trying to find a better understanding for the sample behaviors in the reaction conditions. The catalysts were evaluated in the steam reforming and partial oxidation of methane. In the Pt/CeO2-La2O3-Al2O3 catalysts, the substitution of La for Ce caused a higher stability of CeIII in the alumina structure and higher metal electron density. The oxidation at high temperature caused the Pt agglomeration, on the other hand the reduction treatment lead to a support re-dispersion. The mixed oxides samples with elevated ceria content showed higher activity in the steam reforming and partial oxidation of methane. This behavior was attributed to the ability of promoting the gasification of coke. For the Pt/CeO2-ZrO2-Al2O3 samples, the solid solution between CeO2 and ZrO2 was dependent on the calcination temperature. Phase segregation was observed for the sample calcined at 950ºC, which decreased the catalytic activity. It was attributed to a smaller O* mobility in this sample. / Catalisadores de Pt suportados em óxidos mistos de CeO2-La2O3-Al2O3, com diferentes composições do óxido misto, e CeO2-ZrO2-Al2O3, preparados por três diferentes rotas de adição destes óxidos na alumina, foram sintetizados por meio da técnica sol gel. As amostras tiveram suas propriedades estruturais caracterizadas por meio de técnicas de análise térmica, adsorção de N2, difração de raios X, espectroscopia de refletância difusa, espectroscopia no infravermelho do CO adsorvido, medida de dispersão metálica aparente pela reação de desidrogenação do cicloexano e microscopia eletrônica de transmissão de alta resolução. Com o intuito de um maior esclarecimento dos comportamentos dos catalisadores quando submetidos a condições semelhantes à atmosfera de reação, estudos de oxiredução in situ foram realizados para as amostras e monitorados pelas técnicas de redução a temperatura programada e espectroscopia de alta resolução da borda de absorção. O desempenho catalítico dos catalisadores foi avaliado nas reações de reforma a vapor e oxidação parcial do metano. No que se refere às amostras de Pt/CeO2-La2O3-Al2O3 pode-se afirmar que a substituição do La pelo Ce ocasionou a maior estabilidade do CeIII na rede da alumina e a formação de sítios de Pt com maior densidade eletrônica. O tratamento de oxidação em alta temperatura ocasionou a aglomeração da fase ativa, enquanto que sob condições redutoras, os suportes a base de céria apresentaram um comportamento de re-dispersão. Os maiores valores de atividade nas reações de reforma a vapor e oxidação parcial do metano foram evidenciados para as amostras suportadas nos óxidos mistos com o maior teor de céria. Este resultado foi atribuído a maior interface entre metal-suporte o que proporcionou uma maior transferência de O* para a partícula de Pt, auxiliando na remoção de coque da superfície do catalisador. Para as amostras suportadas nos óxidos mistos de CeO2-ZrO2-Al2O3, a formação da solução sólida entre os óxidos de cério e zircônio demonstrou-se bastante depende da temperatura de calcinação do suporte, apresentando segregação de fases após a calcinação a 950 ºC, e diminuição na atividade catalítica na reação de oxidação parcial do metano em torno de 15%. Este comportamento foi relacionado à menor mobilidade de O* desta amostra, ocasionada pela a separação das fases em CeO2 e ZrO2.