Improvements in selectivity and stability of Rh catalysts modified by SnBu₄. dehydrogenation of isobutane to isobutene

RhSn/SiO2 bimetallic catalysts prepared via an organometallic route have proved to be very active and selective toward several hydrogenation reactions. In this work these catalysts were studied for the dehydrogenation of isobutane to isobutene. It was found that Rh/SiO2 monometallic catalysts had a null selectivity to isobutene, and this selectivity increased up to more than 90% after the addition of tin, using SnBu4 as precursor.Facultad de Ciencias Exacta

Nouvelles raisons d’agir des acteurs de la pêche et de l’agriculture

Les acteurs de la pêche et de l’agriculture (professionnels, institutions d'enseignement, techniciens, organisations professionnelles et syndicales, politiques et législateurs, chercheurs, consommateurs…) font l'expérience de l’évolution des techniques et des droits à produire et à prélever la ressource vivante. Les agriculteurs et les pêcheurs se questionnent sur les raisons de faire leur métier, de s’y maintenir et de le transformer par de nouveaux modes de transmission, de débat et par de nouvelles solidarités. Les auteurs, des chercheurs en sciences sociales et des professionnels des deux filières, examinent les situations les plus propices au développement de nouvelles raisons d'agir et de nouveaux savoirs : débats sur la gestion des ressources renouvelables, décisions relatives au contenu du métier et à sa transmission, mutations professionnelles ou encore nouvelle division du travail. Les situations présentées permettent un éclairage contrasté des secteurs de la pêche et de l'agriculture, et plus particulièrement : – de l’évolution des raisons d’agir et des savoirs des professionnels, des scientifiques, des législateurs mais aussi des nouveaux arrivants, notamment dans leur rapport à l’écologie. Comment de nouvelles raisons d’agir et de nouveaux savoirs émergent-ils des divisions et des conflits ? – des transformations du travail et de la formation professionnelle dans les deux secteurs. Comment les référentiels de formation et les pratiques didactiques modifient-ils les enjeux cognitifs, environnementaux, économiques et sociaux des activités de pêche et d’agriculture ? Ces questions majeures intéresseront à la fois les pêcheurs et les agriculteurs, les concepteurs de politiques publiques et les scientifiques

Extraction des métaux lourds de l eau par réaction avec l hydrogène adsorbé sur une surface de Nickel

For public health and environment protection, heavy metals have to be removed from industrial aqueous efluents before discharges. Several technologies (in exchange resins, electrochemistry, cementation, distillation...) are available to companies but have some limits in efficiency. We propose the concept of a new process for heavy metal removal based on the reaction of the metallic pollutants with the hydrogen adsorbed on a nickel surface. The metallic ions in water are reduced by chemisorbed hydrogen and deposited on the nickel particles. This process decreases the concentrations in organometallics too and is not sensitive to the presence of mineal salts. Only H3O+ or OH- ions easily neutralized are produced. After treatment on alumina supported nickel under hydrogen, the concentrations in Cd2+, Co2+, Ni2+ or Cr2O72- of aqueous solutions are decreased more than 99%LYON1-BU.Sciences (692662101) / SudocSudocFranceF

Adsorption du benzène gazeux sur le nickel de raney étudiée par méthode magnétique et molécules marquées

L'adsorption du benzène sur le nickel de Raney a été étudiée par mesure des variations de l’aimantation à saturation. Deux espèces de benzène chimisorbé ont été détectées. La première, observée sur une surface dégazée, diminue l’aimantation à saturation de 4,6 Magnétons de Bohr par molécule, la seconde produit une baisse d’aimantation nettement plus faible et s’observe sur des surfaces fortement recouvertes en hydrogène. Ces deux espèces sont hydrogénables en cyclohexane et échangeables par du benzène provenant de la phase gazeuse. L’existence de complexes de benzène triosmié en chimie de coordination nous a suggéré un modèle permettant de rendre compte des observations expérimentales

SELECTIVE HYDROGENATION ON PLATINUM NANOPARTICLES STABILIZED BY ORGANOSILANES

Nanoparticles are widely used in heterogeneous catalysis and generally, they are supported on oxides such as silica or alumina. Unfortunately, strong interactions between support and particles exist and lead to the modification of the particles’ properties which means that no unique active sites are obtained. Other side phenomena like diffusion or migration of adsorbed atoms towards the support surface are observed and undesired reactions (isomerization, cyclization,…) with the acid sites take place. Unsupported metal nanoparticles do not interact with a support. Their properties can be modified depending on their size especially in the order of magnitude between 1 and 10 nm. This makes unsupported nanoparticles interesting candidates for fine chemical catalytic applications since no side phenomena occur and active sites are well defined. Surface Organometallic Chemistry on Metals allows controlling the coordination sphere of the active metal by an organometallic fragment. By changing “at will” the steric and electronic properties of the organometallic fragment, it is possible to influence the chemio- , stereo- and regio-selectivity of reactions catalyzed by metallic surfaces. Pt is considered to be a very good catalyst for selective hydrogenation; in particular for enantioselective hydrogenation of alpha ketoesters and it is believed to be less hydrolyzing than Ru. Unsupported Pt nanoparticles were prepared following the procedure already described for Ru, using Pt(dba)2 as precursor and octylsilane (C8SiH3) or vinylphenylmethylsilane (VPMSiH) as stabilizer. The size and the structure of the nanoparticles were determined by TEM and the grafted organometallic fragments were characterized by solid state 1H and 13C CP-MAS NMR, IR and elementary analysis. Crystalline Pt nanoparticles (see Figure) of about 2 nm corresponding to a cubo-octahedron with 3 edge atoms, covered by organosilane fragments were obtained. These nanoparticles are active and chemio-selective in the hydrogenation of cetopentoylactone into the corresponding alcohol and their properties were compared to silica supported Pt

Passive vector geoacoustic inversion in coastal areas using a sequential unscented Kalman filter

An unscented Kalman filter (UKF) for geoacoustic inversion using scalar and vector sound fields created by a passing ship is discussed in this paper. The continuous sound field emitted by a ship of opportunity is processed by the sequential filtering technique to estimate slowly changing environmental properties along the source range. The inversion problem is solved by the UKF with a random-walk parameter model, which is expected to perform well when dealing with highly nonlinear problems. Synthetic geoacoustic inversions are performed using multi-frequency pressure, vertical particle velocity and waveguide impedance (a ratio between pressure and vertical particle velocity) data for the geoacoustic model of a mud environment offshore at the mouth of the Amazon River in Brazil (CANOGA 12). For the preliminary tests, the sound source is composed of a flat spectrum. Numerical results demonstrate that the sequential filtering technique is capable of estimating the evolution of environmental properties along the source range. In practice, ship data have complex time-varying spectral characteristics that can greatly limit the accuracy of broadband or multi-frequency passive applications. Since the vertical waveguide impedance is independent of the source spectral level, it is preferred for environmental characterization by the sound field generated from a ship of opportunity. Because of this independence property, the vertical waveguide impedance is expected to yield a more reliable inversion than that of pressure or vertical particle velocity field. © 2013 CUST.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Inversion for time-evolving sound-speed field in a shallow ocean by ensemble Kalman filtering

info:eu-repo/semantics/publishe

Range-resolving shallow water acoustic tomography by ensemble Kalman filtering

info:eu-repo/semantics/publishe