Surpoids et maladie carieuse chez les enfants de 6 et 9 ans scolarisés en Nouvelle-Calédonie

CLERMONT FD-BCIU Odontol. (631132226) / SudocCLERMONT FD-BCIU-Santé (631132104) / SudocSudocFranceF

Une étude combinée XPS et ToF-SIMS pour une meilleure compréhension de la réactivité du formaldéhyde adsorbé à la surface d'une birnessite

National audienc

Effets des traitements de vieillissement sur les performances en décomposition catalytique de N2O du système Pd/LaCoO3:

Présentation : J.P. Dacquin ORAL 26-28/05/0

Support-induced effect on the catalytic properties of Pd particles in water denitrification: Impact of surface and structural features of mesoporous ceria-zirconia support

International audienceThe support effect on the catalytic properties of palladium particles has been investigated in the reduction of nitrites by hydrogen at 20 °C in batch conditions. The support material was composed of ceria-zirconia mixed oxide stabilized in the tetragonal structure according to an Evaporation Induced Self-Assembly method. In comparison, a co-precipitation method leads to inhomogeneity in composition related to the partial segregation of the cubic fluorite structure of CeO2. Further textural properties obtained for the two synthesis routes differ as well as changes in the reducibility. Surface analysis demonstrated a more extensive surface reduction of Ce4+ to Ce3+ on the series prepared by coprecipitation correlated to a greater stabilization of metallic Pd particles. However, the best catalytic performances were obtained on low loaded Pd samples supported on the ceria-zirconia support prepared by the Evaporation Induced Self-Assembly method which emphasizes the fact that catalytic properties cannot be simply explained by the stabilization of zero valent precious metal at the vicinity of anionic vacancies. Further calculations of TOF and interfacial rates were achieved and compared to the selectivity behavior suggesting that the localization of Pd in contact with the tetragonal or cubic structure of the solid solution and CeO2 could play a key role in determining the catalytic properties

NiAlxFe2−xO4 mixed oxide catalysts for methane reforming with CO2: Effect of Al vs Fe contents and precursor salts

International audienceNiAlxFe2−xO4 (0 ≤x ≤ 2) was synthesized, characterized and evaluated in methane reforming with CO2 without any pretreatment. It was shown that the nature of the precursor has a significant effect on the structural, textural and reactivity properties. The cell parameters decrease with increasing Al-content which can be explained by the partial substitution of Fe3+ ions (∼0.63 Å in tetrahedral site and ∼0.78 Å and high spin in octahedral site) by Al3+ ions (∼0.53 Å) either in the tetrahedral or the octahedral sites. If, on the one hand, the catalytic activity of the aluminum compound exhibits high CH4 and CO2 conversions as well as excellent syngas selectivity, on the other hand, a poor activity is observed for NiFe2O4 whatever the precursors. For low temperatures (T < 750 °C), powders prepared with chlorides are more active than powders prepared with nitrates. However, this behavior mitigates at high temperature. NiAl2O4 issued from nitrate precursors shows the best catalytic performances. Negligible contributions to WGS Reaction are illustrated by H2/CO ratios close to stoichiometry. The intermediate FeAl2O4 spinel phase plays an important role as catalytic precursor in the in-situ production of Ni° nanoparticles, highly dispersed and less prone to coke formation in spite of the severe reaction conditions. A lack of affinity of Al-species to combine with Ni° to form detrimental Ni-Al alloy is proposed to explain the good performances. Strong interactions developed between metallic active sites and mixed oxides substrates allow the stabilization and improvement of catalytic performances in dry reforming of methane.NiAlxFe2-xO4 (0 ≤x ≤ 2) a été synthétisé, caractérisé et évalué dans le reformage du méthane avec du CO2 sans aucun prétraitement. Il a été montré que la nature du précurseur a un effet significatif sur les propriétés structurelles, texturales et de réactivité. Les paramètres de maille diminuent avec l'augmentation de la teneur en Al, ce qui peut s'expliquer par la substitution partielle des ions Fe3+ (∼0.63 Å dans le site tétraédrique et ∼0.78 Å et un spin élevé dans le site octaédrique) par des ions Al3+ (∼0.53 Å) soit dans le site tétraédrique soit dans le site octaédrique. D'une part, l'activité catalytique du composé d'aluminium présente des conversions élevées de CH4 et de CO2 ainsi qu'une excellente sélectivité du gaz de synthèse. D'autre part, une faible activité est observée pour NiFe2O4 quels que soient les précurseurs. Pour les basses températures (T < 750 °C), les poudres préparées avec des chlorures sont plus actives que les poudres préparées avec des nitrates. Cependant, ce comportement s'atténue à haute température. Le NiAl2O4 issu des précurseurs de nitrates montre les meilleures performances catalytiques. Des contributions négligeables à la réaction WGS sont illustrées par des rapports H2/CO proches de la stœchiométrie. La phase spinelle intermédiaire FeAl2O4 joue un rôle important en tant que précurseur catalytique dans la production in-situ de nanoparticules de Ni°, hautement dispersées et moins sujettes à la formation de coke malgré les conditions de réaction sévères. Un manque d'affinité de l'espèce Al à se combiner avec Ni° pour former un alliage Ni-Al nuisible est proposé pour expliquer les bonnes performances. Les interactions fortes développées entre les sites actifs métalliques et les substrats d'oxydes mixtes permettent la stabilisation et l'amélioration des performances catalytiques dans le reformage à sec du méthane

Reaction of formaldehyde over birnessite catalyst: A combined XPS and ToF-SIMS study

International audienceBirnessite with very high surface area (>180 m2 g−1) has been prepared by oxidation of Mn(NO3)2 with H2O2 in KOH solution. The catalytic performance of this free noble metal based material for the formaldehyde (HCHO) selective conversion into CO2 is excellent. Therefore this birnessite material has been selected for X-ray photoelectron spectroscopy (XPS) analysis in combination with time-of-flight secondary ion mass spectroscopy (ToF-SIMS) study to understand the mechanistic interaction between adsorbate and adsorbent. Thermo-desorption of formaldehyde saturated birnessite has been conducted under argon atmosphere, using a catalysis cell allowing the monitoring of the birnessite surface modification. XPS study shows (i) the partial oxidation of formaldehyde at room temperature through the formate species formation and manganese species reduction and (ii) the generation of carbonate species with temperature. ToF-SIMS analyses gave more insight in the kind of cations from birnessite interacting with adsorbed molecules: formate ions interact with manganese and potassium ions while carbonate ions interact only with potassium ions. Formate oxidation takes place on Mn ions to give COx(g) species while formate ions readily decompose on K+ sites at higher temperature

Influence of electrode geometry on the homogeneity of plasma-polymerized methyl methacrylate coatings

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Structure of the water-splitting photocatalyst oxysulfide α-LaOInS₂ and ab initio prediction of new polymorphs

International audienceWe unveil the structure and investigate the visible light watersplitting photocatalyst &alpha;-LaOInS2, the second polymorph in this composition. This remarkable oxysulfide exhibits rare mixed anion InS5O octahedra leading to both O-2p and S-3p hybridized with indium states in the vicinity of the Fermi level. Ab initio structure prediction shows the stability of such heteroleptic environments and points other hypothetical polymorphs