Provider: - Institution: - Data provided by Europeana Collections- The chemistry of platinum complexes is important from the biological and medical point of view. Some Pt(II) complexes, viz. ...cisplatin, carboplatin and oxaplatin, are extensively used in chemotherapy as anticancer drugs. Over the last 40 years many other platinum drugs have been developed in an attempt to improve on isplatin. More recently, there have been efforts to direct the design of non-classical platinum complexes, such as orally active Pt(IV) complexes, sterically hindered Pt(II) complexes, polinuclear Pt(II) complexes, sulfur-containing platinum complexes, etc. Although the precise mechanism of a anti-tumour action of platinum drugs is not completely understood, the activity has been explained by the interactions between the complex and DNA primarily by forming bifunctional adducts. Experiments have demonstrated that cisplatin binding to DNA is kinetically rather than thermodynamically controlled. However, the application of platinum drugs has been greatly hampered by drug resistance and several side effects. Moreover, poor solubility in aqueous solution is also inconvenient in clinical use. There are many other potential biomolecules that can also react with these Pt(II) complexes, such as small molecules, proteins and enzymes. In fact, already in blood, where the Pt drug is administered by injection or infusion, several molecules are available for kinetic and thermodynamic competition. The binding to DNA eventually leads to an altered protein conformation and changes in biological activity, especially when enzymatic reactions are affected. Sulfur-containing molecules have a high affinity for platinum and could form very stable bonds. Moreover, the interaction of Pt complexes with sulfur-containing biomolecules has been associated with negative phenomena such as nephrotoxicity, gastrointestinal toxicity, ototoxicity, cardiotoxicity and neurotoxicity. Competition studies of Pt(II) complexes with L-met and 5’-GMP have demonstrated that a transfer from thioether ligand to N7-guanine site can occur, with the result that such Pt- S(thioether) adducts can presumably serve as a drug reservoir for platination at DNA. Although such substitution of thioether by guanine seems to be common, any measurable transformation from Pt-S(thiol) to Pt-N7 coordination was not observed. For kinetic and mechanistic studies, Pd(II) complexes are suitable model compounds since they react ca. 104-105 times faster than their Pt(II) analogues, whereas their strucural and equilibrium behaviour are very similar. Because of their strong affinity towards S and N donor ligands, as well as their high reactivity, the selectivity of certain Pd(II) complexes towards biomolecules is lower, limiting the possibility of developing compounds with antitumor reactivity. In recent years, however, it has been shown that certain Pd(II) complexes can also show antitumor activity. Here, we reported the obtained results for substitution of different Pt(II) and Pd(II) complexes with sulfur- and nitrogen-donor nucleophiles. The obtained results are presented in this order: • The substitution reactions of PtCl(bpma)+, PtCl(gly-met-S,N,N), Pt(bpma)H2O2+ and Pt(gly-met-S,N,N)H2O+ with L-met, GSH and 5’-GMP were studied in aqueous solutions in 0.1 M NaClO4 under the pseudo-first-order conditions as a function of concentration and temperature using UV-VIS spectrophotometry. The reactions of the chlorido complexes were followed in the presence of 10 mM NaCl and at pH ca. 5, whereas the reactions of the aqua complexes were studied at pH = 2.5. The PtCl(bpma)+ complex is more reactive towards the selected nucleophiles than PtCl(gly-met-S,N,N). Also, the aqua complexes are more reactive than the corresponding chlorido forms. The activation parameters for all studied reactions suggest an associative substitution mechanism. The reactions of PtCl(bpma)+ and PtCl(gly-met-S,N,N) with 5’-GMP were studied by using 1H NMR spectroscopy at 298 K. The pKa values of the Pt(gly-met-S,N,N)H2O+ complex is 5.95. DTF calculations at the B3LYP/LANL2DZp hybrid density functional calculations show that the DFT energy for Pt-N7(guo) (guo is guanosine) is much lower than Pt-S(thioether). In all cases the guanine coordination to the L3Pt (L3: terpy, bpma, dien and gly-met-N,N,S) fragment is much more favorable than the thioether coordinated form. The calculations collectively support the experimentally observed substitution thioethers from Pt(II) complexes by N7-GMP. This study could throw more light on the mechanism of the active platinum antitumor complexes. • Substitution reactions of the complexes cis-Pt(NH3)2Cl2, Pt(SMC)Cl2-, Pt(en)Cl2 and Pt(dach)Cl2, with selected biologically important ligands, viz. 5’-GMP, L-his and 1,2,4- triazole, were studied. All reactions were studied in aqueous 25 mM Hepes buffer in the presence of 5 mM NaCl at pH = 7.2 under pseudo-first-order conditions as a function of concentration at 310 K using UV-VIS spectrophotometry. Two consecutive reaction steps, which both depend on the nucleophile concentration, were observed in all cases. The second-order rate constants for both reaction steps indicate a decrease in the order Pt(SMC)Cl2- > cis-Pt(NH3)2Cl2 > Pt(en)Cl2 > Pt(dach)Cl2. DFT calculations (B3LYP/LANL2DZp) showed that the Pt-N7(Guo) adduct in the gas phase is more stable than Pt–S(thioether) by ca. 31–33 kcal/mol for the studied complexes cis-Pt(NH3)2Cl2, Pt(SMC)Cl2- and Pt(en)Cl2. The calculations collectively support the experimentally observed substitution of thioethers bound to Pt(II) complexes by N7(5’-GMP). Finally, this result clearly show how much the Pt-N7(Gua) adduct is more stable than the Pt- S(thioether). • Two new complexes with bis(imidazolin-2-imino) ligands, (TLtBu)PdClClO4 and (BLiPr)PdCl2, were synthesized. The crystal structures of these complexes were determined by X-ray diffraction. The coordination geometries around the palladium atoms are distorted square-planar, with the Pd-N1 distance to the central nitrogen atom of the TLtBu ligand, 1.944(2), being shorter than those to the other two nitrogen atoms of TLtBu, viz. 2.034(3) and 2.038(3) Ǻ. The BLiPr complex displays similar Pd-N distances of 2.031(2) and 2.047(2) Å.The kinetics and the mechanism of the substitution reactions of the (TLtBu)PdCl+ complex, with nucleophiles 5’-GMP, L-met and L-his were studied using variable-temperature stopped-flow techniques in aqueous 0.1 M NaClO4 with 10 mM NaCl at 298 K. The order of reactivity of ligands is: L-met > 5’-GMP > L-his. The complex formation equilibria of (BLiPr)Pd(H2O)22+ and (TLtBu)Pd(H2O)2+ with some biologically relevant ligands (L-met, 5’-GMP and L-his) were also studied. The stoichiometry and stability constants of the newly formed complexes are reported, and the concentration distribution of the various complex species has been evaluated as a function of pH. Comparing the values of logβ1,1,0 for 5’-GMP, L-his and L-met complexes, the most stable complex is complex with 5’-GMP followed by L-his and Lmet for both complexes, (BLiPr)Pd(H2O)22+ and (TLtBu)Pd(H2O)2+. • Substitution reactions of the complexes Pt(bpma)H2O2+ and PtCl(bpma)+, with the nitrogen-donor ligands 1,2,4-triazole, pyrazole and pyridazine were studied in aqueous 0.1 M NaClO4 using variable-temperature UV-VIS spectrophotometry. The reactions of the aqua complex were studied at pH 2.5 and those of the chlorido complex were studied in the presence of 10 mM NaCl to prevent their hydrolysis. The values obtained for the second-order rate constants indicate that the complexes with bpma are more reactive then those with diethylenetriamine. In both cases the aqua complexes are more reactive than the corresponding chlorido complexes. The reactivity of the incoming ligands follow the order: 1,2,4-triazole > pyridazine > pyrazole. Activation parameters were determined for all the reactions and the negative entropies of activation (ΔS≠) support an A or Ia mechanism.- Ispitivanje kompleksa platine značajno je sa biološkog i medicinskog aspekta. Neki kompleksi Pt(II) kao što su cisplatina, karboplatina i oksaliplatina intezivno se koriste u hemoterapiji kao antitumorski reagensi. Poslednjih 40 godina veliki broj drugih platinskih jedinjenja sintetisano je sa ciljem da se postigne bolja aktivnost u odnosu na cisplatinu. Nedavno, počelo se sa sintezom neklasičnih platiniskih kompleksa, kao što su Pt(IV) kompleksi, koji mogu oralno da se upotrebljavaju, sterno zaštićeni Pt(II) kompleksi, polinuklearni Pt(II) kompleksi, kompleksi platine koji sadrže sumpor, itd. Mada tačan mehanizan kojim Pt(II) kompleksi ispoljavaju svoju antitumorsku aktivnost nije potpuno jasan, smatra se da svoju aktivnost kompleksi Pt(II) ispoljavaju interakcijom sa molekulom DNK, formirajući bifunkcionalni proizvod. Eksperimenti su pokazali da je vezivanje cisplatine za DNK kinetički a ne termodinamički kontrolisan proces. Međutim, upotreba platinskih antitumorskih jedinjenja ograničena je pojavom sporednih efekata i rezistentnosti. Takođe, mala rastvorljivost u vodenim rastvorima je dodatni efekat koji umanjuje kliničku upotrebu ovih jedinjenja. Postoji veliki broj biomolekula koji mogu da reaguju sa kompleksima Pt(II), kao što su mali molekuli, proteini i enzimi. Već u krvi, gde antitumorsko jedinjenje Pt(II) biva uneto putem injekcije ili infuzijom, postoji nekoliko molekula koji mogu da se vežu sa Pt(II) kompleksom. Vezivanje za DNK vodi do promene u konformaciji proteina i biološkoj aktivnosti, naročito kada su u pitanju enzimske reakcije. Sumpor-donorski molekuli imaju veliki afinitet prema platini i formiraju jako stabilnu vezu. Upravo interakcija kompleksa Pt(II) sa sumpor-donorskim biomolekulima povezana je sa sporednim efektima kao što su nefrotoksičnost, gastro-toksičnost, ototoksičnost, kardiotoksičnost i neurotoksičnost. Ispitivanja konkurentnih reakcija kompleksa
This article surveys the amount of projects registered by Centro de Artes e Letras – CAL, from the Universidade Federal de Santa Maria – UFSM, from 1992 to 2008 in which the themes discussed are ...related to the Platine region and/or to the Southern Common Market – Mercosur. In order to develop the survey, a report was requested and emitted by Centro de Processamento de Dados – CPD, through Sistema de Informações para o Ensino – SIE. The data surveyed were related to types, situation and origin of the projects, which could come from undergraduate or graduate students, as well as other relevant information about the projects. The research was made under a quantitative approach and the theme was investigated from the perspective of databank as a documental patrimony, which needs to be managed in a way to ensure the authenticity and reliability of the documents, as well as guarantee the availability of all these relevant information for society.
Neste artigo, é feito um levantamento sobre o número de projetos registrados no âmbito do Centro de Artes e Letras (CAL), da Universidade Federal de Santa Maria (UFSM), no período 1992/2008, com temáticas referentes à região Platina e/ou ao Mercado Comum do Sul (MERCOSUL). Para esse levantamento, utilizou-se relatório solicitado e emitido pelo Centro de Processamento de Dados (CPD), através do Sistema de Informações para o Ensino (SIE). Foram levantados os números em relação aos tipos de projetos, situações e sua origem – se de graduação, ou de pós-graduação, além de outras informações pertinentes a projetos. A análise dessas informações foi feita a partir de uma abordagem quantitativa e tratou-se o tema sob enfoque do banco de dados como patrimônio documental. Enfatiza-se que o referido banco de dados deve ser administrado de forma a garantir a autenticidade e a fidedignidade dos documentos, assim como viabilizar o acesso deles à sociedade.
El trabajo computó el número de proyectos registrados en el ámbito del Centro de Artes e Letras - CAL de la Universidade Federal de Santa Maria - UFSM, en el período de 1992 a 1998, con temáticas referentes a la región del Plata y/o al Mercado Común del Sur - MERCOSUR. Para desarrollar esta investigación, se utilizó un informe que el Centro de Procesamiento de Datos – CPD solicita y emite mediante el Sistema de Informaciones para la Enseñanza - SIE. Se computó los números referentes a tipos de proyectos, situaciones y origen - si procedía del curso de grado o posgrado, como otras informaciones relevantes. Para el análisis, de abordaje cuantitativa, se trató el tema considerando la base de datos como patrimonio documental, y que este debe ser administrado de modo a que garantice la autenticidad y credibilidad de los documentos como también permita el acceso a la sociedad.
The Reactivity of Dinuclear Platina‐β‐diketones with Phosphines: Diacetylplatinum(II) Complexes and Mononuclear Platina‐β‐diketones
Addition of mono‐ and bidentate phosphines or of AsPh3 to the ...platina‐β‐diketone Pt2{(COMe)2H}2(μ‐Cl)2 (1) followed by the addition of NaOMe at −70 °C resulted in the formation of diacetyl platinum(II) complexes cis‐Pt(COMe)2L2 (L = PPh3, 2a; P(4‐FC6H4)3, 2b; PPh2(4‐py), 2c; PMePh2, 2d; AsPh3, 2d) and Pt(COMe)2(L⌢︁L) (L⌢︁L = dppe, 3b; dppp, 3c), respectively. The analogous reaction with dppm afforded the dinuclear complex cis‐{Pt(COMe)2}2(μ‐dppm)2 (4) that reacted in boiling acetone yielding Pt(COMe)2(dppm) (3a). The reactions 1 → 2/3 were found to proceed via thermally highly unstable cationic mononuclear platina‐β‐diketone intermediates Pt{(COMe)2H}L2+ and Pt{(COMe)2H}(L⌢︁L)+, respectively, that could be isolated as chlorides for L⌢︁L = dppe (5a) and dppp (5b). The reversibility of the deprotonation of type 5 complexes with NaOMe yielding type 3 complexes was shown by the protonation of the diacetyl complex 3b with HBF4 yielding the platina‐β‐diketone Pt{(COMe)2H}(dppe)(BF4) (5c). All compounds were fully characterized by means of NMR and IR spectroscopies, and microanalyses. X‐ray diffraction analysis was performed for the complex cis‐Pt(COMe)2(PPh3)2·H2O·CHCl3 (2a·H2O·CHCl3).
By attracting male orchid bees with eight chemical baits in the gallery forest of the Parque Nacional da Chapada dos Guimarães, southern Mato Grosso state, Brazil, I found several males belongs to ...all Euglossini bee genera. Male euglosine bees were collected monthly using an entomological net as they arrived at the baits. From September 2003 to July 2005, the baits were applied to absorbent paper pads from 8:00 AM to 4:00 PM. From 24 collections, a total of 264 males were captured, spread throughout the five genera of the tribe and belonging to 30 valid species. Of all the males collected, only one was Euglossa cognata Moure, reported to occur from Costa Rica to southern Brazil, and herein recorded to the Platina Basin for the first time. The results clarify the distributional gap and amplified the geographic distributional range of E. cognata in South America.
Cette étude traite de la préparation de nanomatériaux à base de palladium et de platine qui ont une morphologie contrôlée, et de la caractérisation de leur activité électrocatalytique vis-à-vis de ...l'oxydation de l'éthanol, l'éthylène glycol et le glycérol en milieu alcalin. La détermination des différentes propriétés de ces matériaux utilisés comme catalyseurs anodiques a permis la compréhension des étapes clés et l'élucidation des principaux chemins réactionnels impliqués dans la conversion électrochimique de ces alcools utilisables comme combustible dans une pile.Dans ce contexte, ces nanomatériaux ont été synthétisés soit par la méthode d'auto-assemblage électrostatique, soit par la méthode polyol assistée par microondes. Ces méthodes de synthèse chimique choisies car plus adaptées à cette fin, ont permis d'obtenir des nanoparticules de type cœur@coquille dont les atomes de palladium ou de platine sont situés dans la coquille, et le cœur constitué de nickel, ruthénium ou d'étain. Nanomatériaux synthétisés par auto-assemblage électrostatique - Par souci d'économiser les métaux nobles et précieux, sans pour autant perdre en activité, les électrocatalyseurs synthétisés par auto-assemblage électrostatique ont été dispersés dans du carbone Vulcan XC-72R ou déposés sur des Nanotubes de Carbone (NTC) avec un taux de charge métallique de wt. 40%. Les résultats issus des différentes caractérisations physicochimiques ont montré que les matériaux préparés ont des compositions expérimentales (par Spectroscopie de Rayons-X à Dispersion d’Énergie – EDX) similaires aux valeurs nominales ; les paramètres de maille et volume des particule varient légèrement pour les différents matériaux (Microscopie Electronique en Transmission – MET et Diffraction des Rayons X – DRX), mais ont gardé le caractère cristallographique de la structure cubique à faces centrées du palladium et du platine. Les nanoparticules obtenues sont en général de forme sphérique et ont une taille comprise entre 2 et 9 nm ; leur morphologie indique des systèmes très organisés, mais leur structure coeur@coquille n'a pour l'instant pas été formellement déterminée. Des expériences de CO-Stripping ont permis de caractériser électrochimiquement les surfaces actives les matériaux qui ont été synthétisés. Il en résulte leur surface active augmentent de façon très significative des systèmes monométalliques aux électrodes bimétalliques, en particulier les nanocatalyseurs Ru@Pd/NTC et Ni@Pt/NTC qui ont des surfaces spécifiques respectives de 73 et 74 m²g-1Pd/Pt. Concernant l'électrooxydation des alcools en C2 et C3 dans un électrolyte alcalin (1,0 mol L-1 NaOH + 0,5 mol L-1 alcool), les électrocatalyseurs contenant du platine et déposés sur des nanotubes de carbone ont une meilleure activité électrocatalytique vis-à-vis de l’oxydation du combustible éthylène glycol en termes de densité de courant mesurée à un potentiel de -0,2 V vs. Hg/HgO/OH-. Par exemple, sur l’électrode de composition Ni@Pt/NTC, il a été relevé en début d’expérience de chronoampérométrie une densité de courant de 200 mA mg-1Pt qui a seulement baissé à 180 mA mg-1Pt après une étude qui a duré 90 minutes.Des analyses par chromatographie liquide (CLHP) ont été entreprises pour déterminer les molécules issues de l’oxydation des combustibles susmentionnés. Les taux de conversion de l'éthylène glycol et du glycérol ont respectivement atteint 74 et 58 % après 12 heures d'électrolyse par chronoampérométrie sur les catalyseurs Ru@Pt/NTC et Ni@Pt/NTC. Si l’oxydation du glycérol produit sélectivement des ions formiate et oxalate sur Ru@Pt/NTC, elle conduit majoritairement aux ions tartronate et mesoxalate sur l’électrode Ni@Pt/NTC, révélant ainsi deux chemins réactionnels de la transformation électrochimique du combustible glycérol selon la structure cœur-coquilles du matériau bimétallique.
The present study proposes the synthesis of nanocatalysts based on palladium and platinum with high morphological organization and investigates their catalytic activity for the electrooxidation of ethanol, ethylene glycol, and glycerol in alkaline medium, seeking to understand the steps and mechanisms involved in these reactions. The nanomaterials were synthesized by the electrostatic self-assembly method and by the polyol microwave-assisted method. The goal was to obtain nanoparticles with morphology inspired by the core@shell-type systems, where the shell layer consists of platinum or palladium, and the core contains nickel, ruthenium, or tin. The electrocatalysts synthesized by the electrostatic self-assembly method were supported on Carbon Vulcan XC-72R or Multi-Walled Carbon Nanotubes (MWCNT, metal/carbon = 40:60). Morphology characterization data indicated uniform spherical shape nanoparticles with size ranging between 2 and 9 nm, besides, the specific morphology point to a particular degree of organization. However, the presence of the core@shell-type system was not confirmed through this analysis. CO-Stripping experiments demonstrated that the electrochemically active surface area of the bimetallic systems increased significantly, particularly for the nanocatalysts Ru@Pd/CNT and Ni@Pt/CNT, whose surface areas were 72.8 and 74.1 m²g-1Pd/Pt² respectively. Concerning the electrooxidation of C2 and C3 alcohols in alkaline medium (1.0 mol L-1 NaOH + 0.5 mol L-1 Fuel), M@Pt/CNT systems exhibited higher catalytic activity, especially when employing ethylene glycol as the fuel, which provided the highest catalytic current at constant potential (Eapp = -0.2 V vs. Hg/HgO/OH-). Specifically, the Ni@Pt/CNT nominal composition presented catalytic activity of 180 mA mg-1Pt. Electrochemical conversion studies were performed with the ethyleneglycol-Ru@Pt/CNT and glycerol-Ni@Pt/CNT systems, and after 12 hours of electrolysis, conversion reached values around 74% and 58%, respectively. Concerning the preferential mechanisms for glycerol electrooxidation, evaluated by liquid chromatography analysis, glycerate and tartronate ions were the major intermediates formed. The Ru@Pt/CNT nanocatalyst was selective for formate and oxalate ions. In addition, Ni@Pd/CNT generated mesoxalate ion during the reaction, suggesting a dual pathway for glycerol conversion, via tartronate and/or mesoxalate ions.The nanostructured materials synthesized by the polyol microwave-assisted method were supported on carbon Vulcan XC-72R with 20% wt. metallic loading. Briefly, the metal cores were synthesized separately for successive deposition of the noble metal, by employing the consecutive reductions technique. We investigated the palladium-based bimetallic catalysts, with ruthenium or nickel metallic cores, for the electrooxidation of ethylene glycol (0.1 mol L-1) in alkaline medium (0.1 mol L-1 NaOH). Morphology characterization data indicated that Pd/C catalyst displayed different nanoparticle shapes, and particle size ranged from 3 to 40 nm. Ru@Pd/C and Ni@Pd/C displayed spherical shape with particle size between 2 and 7 nm and between 3 and 10 nm, respectively. Ni@Pd/C exhibited the higher activity towards ethylene glycol oxidation in alkaline medium, reaching values of about 80 mA mg-1Pd at the end of chronoamperometry experiments. Overall, combination of the results obtained by liquid chromatography-mass spectrometry and infrared spectroscopy in situ showed that oxidation of glycolate ion is the limiting step for ethylene glycol conversion in alkaline medium in the presence of palladium-based catalysts. Lower amounts of glycolaldehyde, glyoxylate, and oxalate ions emerged at the end of electrolysis procedure, and no carbonate arose.
O presente estudo tem como objetivo propor a síntese de nanocatalisadores à base de paládio e platina com elevada organização morfológica e investigar a referente atividade catalítica ao promover a eletro-oxidação do etanol, etilenoglicol e glicerol em meio alcalino, buscando assim compreender as etapas e mecanismos envolvidos perante estas reações. Neste contexto, os nanomateriais foram sintetizados pelo método de automontagem eletrostática e pelo método de poliol assistido por micro-ondas. Estas metodologias foram selecionadas a fim de obter nanopartículas com morfologia inspirada em sistemas do tipo core@shell (núcleo@casca), empregando átomos de paládio ou platina localizados na casca sobre núcleos de níquel, rutênio ou estanho. Os eletrocatalisadores sintetizados via automontagem eletrostática foram suportados em Carbono Vulcan XC-72R ou Nanotubos de Carbono de paredes múltiplas, com razão metal:carbono igual a 40:60. As nanopartículas obtidas apresentaram tamanho que variou entre 2-9 nm, formato esférico em quase sua totalidade e morfologia que indicava a presença de um determinado grau de organização; entretanto não foi confirmada a presença de sistemas do tipo core@shell. Experimentos de CO-Stripping demonstraram um aumento significativo da área eletroquimicamente ativa dos sistemas bimetálicos, com destaque para os nanocatalisadores Ru@Pd/NTC e Ni@Pt/NTC que apresentaram valores de 72,8 e 74,1 m² g-1Pd/Pt² respectivamente. Perante a eletro-oxidação dos álcoois C2 e C3 em meio alcalino (1,0 mol L-1 NaOH + 0,5 mol L-1 Combustível), os sistemas que apresentaram atividade catalítica mais elevada foram M@Pt/NTC, destacando o etilenoglicol como o combustível que propiciou a maior corrente catalítica quando submetido a potencial constante (E = -0,2 V vs. Hg/HgO/OH-). Mais especificamente, a composição Ni@Pt/NTC apresentou ao final dos experimentos de cronoamperometria um valor de atividade catalítica da ordem de 180 mA mg-1Pt. Os estudos de conversão eletroquímica demonstraram que ao empregar os sistemas etilenoglicol-Ru@Pt/NTC e glicerol-Ni@Pt/NTC atinge-se valores de conversão eletroquímica da ordem de 74% e 58%, respectivamente, após 12 horas de eletrólise a potencial controlado. Quanto aos mecanismos preferenciais de eletro-oxidação do glicerol, avaliados empregando análises de cromatografia líquida, foi verifi
Les piles à membrane polymère à échange de protons (PEMFC) sont une des techniques les plus prometteuses pour une production d'électricité propre et efficace à partir d'hydrogène. Les applications de ...cette nouvelle génération de piles à combustibles concernent aussi bien des applications portables et nomades telles que smartphones, ordinateurs portables, électronique embarquée que des applications domestiques ou dans les transports. A ce jour, le platine utilisé comme catalyseur est considéré comme le seul choix possible pour un rendement élevé et stable. En conséquence, suite à des ressources limitées en platine, la fabrication des piles à combustible reste coûteuse et la production industrielle généralisée impossible. Pour cette raison, une diminution substantielle de la quantité de Pt incorporée et donc la recherche de nouveaux matériaux d'anode à faible coût avec une activité élevée sont nécessaires. Des systèmes à base d’oxyde de cérium dopés au platine avaient été présentés comme étant des catalyseurs actifs pour l'oxydation du CO, la production d'hydrogène, l'oxydation de l'éthanol et la décomposition de méthanol. Au cours de ce travail, de nouveaux concepts pour la fabrication des piles à combustible ont été développés : la quantité de platine incorporée a été fortement diminuée conduisant à la production de nouveaux matériaux d'anode. Enfin, des catalyseurs à base de platine ont été déposés non pas sous la forme usuelle de nanopoudres mais sous forme de films minces fortement poreux sur substrat silicium.Au cours de cette thèse, le système Pt-CeOx a été étudié. Des échantillons non dopés puis dopés avec une faible quantité de platine ont été élaborés puis caractérisés en vue d'une application comme catalyseurs pour piles à combustibles. L'obtention de ces matériaux avec des propriétés sur mesure implique la maîtrise totale de leurs conditions de croissance. Afin d’étudier ces nouveaux composés de taille nanométrique, la microscopie électronique en transmission (MET) a été un outil précieux, qui a permis d'apporter des informations très précises sur la morphologie des films minces, la composition chimique et la structure à l'échelle atomique. Le cérium possède un double degré d'oxydation (+III/+IV), ce qui explique ses très bonnes propriétés catalytiques. Des analyses par spectrométrie dephotoélectrons X (XPS) ainsi que par spectroscopie de pertes d'énergie des électrons (EELS) ont été effectuées afin de déterminer son degré d'oxydation.
Present doctoral thesis is focused on investigation of novel metal-oxide anode catalyst for fuel cell application by electron microscopy and associated spectroscopies. Catalysts based on Pt-doped cerium oxide in form of thin layers prepared by simultaneous magnetron sputtering deposition on intermediate carbonaceous films grown on silicon substrate have been studied. The influence of the catalyst support composition (a-C and CNx films), deposition time of CeOx layer and other deposition parameters, as deposition rate, composition of working atmosphere and Pt concentration on the morphology of Pt-CeOx layers has been investigated mainly by Transmission Electron Microscopy (TEM). The obtained results have shown that by combination of suitable preparation conditions we are able to tune the final morphology and composition of the catalysts. The composition of carbonaceous films and Pt-CeOx layers was examined by complementary spectroscopy techniques – Energy Dispersive X-ray Spectroscopy (EDX), Electron Energy Loss Spectroscopy (EELS) and X-ray Photoelectron Spectroscopy (XPS). Such prepared porous structures of Pt-CeOx are promising as anode catalytic material for real fuel cell application.
Předložená dizertační práce se zabývá studiem nových katalyzátorů na bázi kov-oxid vhodných pro použití v palivových článcích na straně anody. Platinou dopovaný oxid ceru připravený magnetronovým naprašováním ve formě tenkých vrstev na uhlíkových mezivrstvách nesených křemíkovým substrátem byl zkoumán prostřednictvím mikroskopických a spektroskopických metod. Vliv složení uhlíkového nosiče (a-C a CNx filmy), depozičního času CeOx vrstvy a dalších depozičních parametrů, např. depoziční rychlosti, složení pracovní atmosféry a Pt koncentrace na morfologii Pt-CeOx vrstev byl studován převážně pomocí transmisní elektronové mikroskopie (TEM). Získané výsledky ukazují, že vhodnou kombinací depozičních podmínek jsme schopni vyladit výslednou morfologii a kompozici katalyzátoru. Složení uhlíkových filmů a Pt-CeOx vrstev bylo studováno spektroskopickými technikami – energiově-disperzní spektroskopií (EDX), spektroskopií charakteristických ztrát elektronů (EELS) a rentgenovou fotoelektronovou spektroskopií (XPS). Takto připravené porézní struktury vrstev Pt-CeOx jsou slibným katalytickým materiálem na straně anody pro reálné aplikace v palivových článcích.
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