Effect of the Nature of Surfactant on the Reactivity of C,N-diphenylnitrone towards Acrylonitrile in Different Microemulsions Systems

The present work provides an insight into the effect of the nature of surfactant (cationic, anionic), a component of water- and oil-borne microemulsions, on the reaction rate of 1,3-dipolar cycloaddition of C,N-diphenylnitrone with acrylonitrile. The electrostatically attractive character of the cationic surfactant, would bring the reactants closer to each other; hence, a rate enhancement would ensue, particularly within the water-rich zone. Besides the fact that acrylonitrile played a dual role, as a component of the microemulsion and a dipolarphile in the cycloaddition reaction, made the work-up advantageously sound. Additionally, the increase in reagents molar ratio was found to promote higher reactivity

Sulfonamides, sulfonates et thiosulfonates inhibiteurs de la lignification : mecanisme de thiolyse de thiosulfonates en milieu organique

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Determination of the exchange current in the SOFC composite cathode

International audienceTo evaluate the exchange current Io of the oxygen electrode reaction at the O2 strontium-doped lanthanum manganite (LSM)/yttria stabilized zirconia (YSZ) composite/YSZ interface, the variation of the current I vs overvoltage η is measured at low cathodic and anodic polarizations (−50 to 30 mV). A linear behavior is observed within this potential domain with a unique slope. Taking into account of the dissociative adsorption of the oxygen molecule on the LSM electrocatalyst surface and the charge transferred at the triple-phase boundary, the exchange current is evaluated to 2.93 mA in air at 747 °C

Étude des propriétés électriques de l'interface La_0,80 Sr_0,20 MnO_3±δ – Y_0,08 Zr_0,92 O_1,96 nanométrique

International audienceDes mesures de conductivité de LSM20 ont été effectuées sous air en fonction de la température (375 à 1273 °K) par la méthode des 4 points. Les échantillons ont été préparés par réaction à l'état solide à partir de mélanges de La2O3, MnCO3 et SrCO3 et frittés à 1673 °K. Les résultats obtenus montrent que la conductivité obéit à une loi de type σ = AT 3/2 exp (–(Ea/kT)) représentative d'un mécanisme de saut activé entre les sites Mn3+ et Mn4+. Des mesures de l'impédance en fonction de la température et de la pression partielle de l'oxygène de l'interface LSM20–n (nanométrique) YZ8 ont été réalisées sur des cellules symétriques avec deux électrodes de LSM20. Les valeurs de la conductivité de l'électrolyte sont très proches de celles obtenues avec des électrodes d'argent (Ag–nYZ8), ce qui montre que la réponse de l'électrolyte est indépendante de la nature du matériau d'électrode. L'étude de la conductivité de l'électrode en fonction de la température donne une énergie d'activation égale à 1,67 eV légèrement inférieure à celles avancées par d'autres auteurs. Le caractère nanométrique de l'électrolyte pourrait être à l'origine de cet écart. La variation de la conductivité de l'électrode en fonction de la pression de l'oxygène obéit à une loi de type σ = σ0 PO21/2 suggérant que l'étape limitante de la réaction d'électrode est l'adsorption dissociative de O2 par le matériau d'électrode. Conductivity of perovskite-type oxide LSM20 was measured in air for different temperatures (375–1273 °K) using the 4 point method. LSM20 was prepared by solid-state reaction starting from mixtures of La2O3, MnCO3, and SrCO3 and sintered at 1673 °K. The results show that conductivity obeys the following law: σ = AT 3/2 exp(–(Ea/kT)), which is representative of an activated jump mechanism between Mn3+ and Mn4+ sites. The LSM20–n (nanometric)YZ8 interface was characterized by impedance spectroscopy. Symmetrical cells with two LSM20 electrodes were used. The electrolyte conductivity values are very close to those obtained with silver electrodes (Ag–nYZ8) showing that the electrolyte response is independent of the nature of the electrode material. The study of the electrode conductivity versus temperature shows an activation energy equal to 1.67 eV slightly lower than that observed by other authors. The nanometric grain size of the electrolyte could be at the origin of this difference. The variation of the electrode conductivity versus oxygen partial pressure is described by the following law σ = σ0 PO21/2, suggesting that the limiting step of the electrode reaction is the dissociative adsorption of O2 on the electrode material

Nanostructured layered double hydroxide aerogels with enhanced adsorption properties.

International audienceAerogels of layered double hydroxides were prepared by a simple and eco-friendly method involving a quick coprecipitation followed by supercritical CO2 drying. Such aerogels display high surface areas and enhanced adsorption behavior