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Bernardi F.,Federal University of Rio Grande do Sul | Traverse A.,Laboratoire Of Chimie Physique | Olivi L.,Elettra - Sincrotrone Trieste | Alves M.C.M.,Federal University of Rio Grande do Sul | Morais J.,Federal University of Rio Grande do Sul
Journal of Physical Chemistry C | Year: 2011

PtxPd1-x (x = 0.5, 0.3, or 0) nanoparticles submitted to hydrogen reduction and posterior H2S sulfidation at 300 °C were characterized by in situ and ex situ X-ray absorption spectroscopy (XAS). The XAS measurements allowed monitoring short-range order changes around the Pt and Pd atoms induced by the thermal processes. Using the structural parameters obtained from the fitting procedure of the extended X-ray absorption fine structure (EXAFS) data, it was observed that the number of chemisorbed sulfur atoms is proportional to the quantity of Pd in the vicinity of Pt. A correlation between the sulfur reactivity of the nanoparticles and the bimetallic interaction effect is then evidenced. © 2011 American Chemical Society.

Nohra B.,University of Versailles | El Moll H.,University of Versailles | Rodriguez Albelo L.M.,University of Habana | Mialane P.,University of Versailles | And 9 more authors.
Journal of the American Chemical Society | Year: 2011

The grafting of the triangular 1,3,5-benzene tricarboxylate linkers (denoted trim) on tetrahedral ε-Keggin polyoxometalates (POMs) capped by Zn(II) ions, formed in situ under hydrothermal conditions, has generated three novel POM-based metal organic frameworks (POMOFs). (TBA)3[PMo V 8MoVI 4O36(OH) 4Zn4][C6H3(COO)3] 4/3̇6H2O (ε(trim)4/3) is a 3D open-framework built of molecular Keggin units connected by trim linkers, with channels occupied by tetrabutylammonium (TBA) counterions. ε(trim) 4/3 is a novel (3,4)-connected net, named ofp for open-framework polyoxometalate, and computer simulations have been used to evaluate its relative stability in comparison with ctn- and bor-like polymorphs, showing the stability of this novel phase directly related to its greatest density. A computational study was also undertaken with the aim of locating TBA molecules, the positions of which could not be deduced from single crystal X-ray diffraction, and further rationalizes their structure directing role. In (TBA)3[PMoV 8MoVI 4O 37(OH)3Zn4][C6H3(COO) 3] (ε2(trim)2), the building unit is not the molecular Keggin but a dimerized form of this POM. Their connection via trim linkers generates a 3D framework with channels filled by TBA cations. In (TBA)3[PMoV 8MoVI 4O 37(OH)3Zn4][C6H3(COO) 3]·8H2O ([ε(trim)]∞), zigzag chains are connected via the organic linkers, forming 2D grids. Modified electrodes were fabricated by direct adsorption of the POMOFs on glassy carbon or entrapment in carbon paste (CPE). A remarkable electrocatalytic hydrogen evolution reaction (HER) was detected with a yield greater than 95%, and a turnover number as high as 1.2 × 105 was obtained after 5 h. The reported POMOF-based electrodes are more active than platinum, with a roughly 260 mV anodic shift. Finally, the electrocatalytic activities of ε(trim)4/3/CPE electrodes in various XCl (X = Li, Na, K, Cs) media have been studied. This allowed us to detect a cation effect and propose an electrocatalytic mechanistic pathway for the HER. © 2011 American Chemical Society.

Al-Oweini R.,Jacobs University Bremen | Bassil B.S.,Jacobs University Bremen | Friedl J.,TUM CREATE | Friedl J.,TU Munich | And 11 more authors.
Inorganic Chemistry | Year: 2014

The five manganese-containing, Keggin-based tungstosilicates [Mn II 3(OH)3(H2O)3(A-α- SiW9O34)]7- (1), [MnIII 3(OH)3(H2O)3(A-α-SiW 9O34)]4- (2), [MnIII 3(OH)3(H2O)3(A-β-SiW 9O34)]4- (3), [MnIII 3MnIVO3(CH3COO)3(A- α-SiW9O34)]6- (4), and [Mn III 3MnIVO3(CH3COO) 3(A-β-SiW9O34)]6- (5) were synthesized in aqueous medium by interaction of [A-α-SiW9O 34]10- or [A-β-SiW9O34H] 9- with either MnCl2 (1) or [MnIII 8MnIV 4O12(CH3COO) 16(H2O)4] (2-5) under carefully adjusted reaction conditions. The obtained salts of these polyanions were analyzed in the solid state by single-crystal X-ray diffraction, IR spectroscopy, and thermogravimetric analysis. The salts of polyanions 1, 2, and 4 were further characterized in the solid state by magnetic studies, as well as in solution by electrochemistry. © 2014 American Chemical Society.

Chettibi S.,University of Mentouri Constantine | Keghouche N.,University of Mentouri Constantine | Benguedouar Y.,University of Mentouri Constantine | Bettahar M.M.,French National Center for Scientific Research | Belloni J.,Laboratoire Of Chimie Physique
Catalysis Letters | Year: 2013

The radiolysis route is applied to synthesize nickel catalysts deposited on titanium dioxide. The TPR profile of radiation-induced Ni/TiO2 catalyst indicates a more complete reduction of the irradiated catalysts compared to the conventionally H2-reduced one. When tested in the benzene hydrogenation, the radiolytic Ni/TiO2 exhibits catalytic properties with higher efficiency than the H2-reduced catalyst. This observation is assigned to the presence of intermetallic Ni-Ti compounds (Ni2.66Ti1.33 and Ni3Ti) evidenced by XRD. In contrast, the calcined and H2-reduced catalyst contains predominantly the oxidized Ni5TiO7 phase, where the nickel is in strong interaction with the support. The TEM observations show highly dispersed nickel. Graphical Abstract: When tested in the benzene hydrogenation reaction, the catalyst Ni/TiO2 prepared by gamma-irradiation exhibits catalytic properties (the turn-over frequency at total conversion is 33.5 molecules Bz Ni at -1 s-1 at 140 C) with higher efficiency and at lower temperature than the H2-reduced catalyst. This observation is assigned to extremely dispersed nickel nanoparticles and to intermetallic Ni2.66Ti1.33 and Ni3Ti compounds evidenced by XRD. [Figure not available: see fulltext.] © 2013 Springer Science+Business Media New York.

Kulesza J.,Technical University of Gdansk | Kulesza J.,Laboratoire Of Chimie Physique | Guzinski M.,Technical University of Gdansk | Hubscher-Bruder V.,Laboratoire Of Chimie Physique | And 2 more authors.
Polyhedron | Year: 2011

The synthesis, characterisation and X-ray crystal structures of p-tert-butyl-calix[4]arene-thioamide L and its complex with lead L-Pb 2+ is reported. The cation-binding properties in solution have been assessed by liquid-liquid extraction of the metal picrates from water into dichloromethane and by stability constants determination in acetonitrile using UV-absorption spectrophotometry or potentiometry. The compound was used as active material in Pb-ion-selective membrane electrodes. The characteristics of these electrodes as well as the selectivity coefficients for Pb 2+ cation versus many metal ions tested were obtained. Complex formation constants within the electrode membranes were determined using the sandwich membrane method and were compared to those obtained in acetonitrile. The lead concentration in the scrap-lead was determined with the use of electrodes incorporating the ligand studied. © 2010 Elsevier Ltd. All rights reserved.

Kulesza J.,Technical University of Gdansk | Kulesza J.,Laboratoire Of Chimie Physique | Bochenska M.,Technical University of Gdansk
European Journal of Inorganic Chemistry | Year: 2011

There is an increasing interest in applying p-tert-butylcalix[4]arenes as sensing materials in ion-selective electrodes (ISEs). Considerable efforts were made to design calixarenes that are selective for some heavy- or transition-metal ions to be used in ISEs for controlling and monitoring the level of such pollutants in the environment. It has been reported that introduction of softer sulfur atoms instead of oxygen atoms in calix[4]arene substituents promotes their complexing ability towards transition- and heavy-metal ions, which are toxic for human beings and pollute the environment. In this microreview, we present sulfur-containing calix[4]arenes acting as sensing materials for metal cations such as Ag+, Pb2+, Cu2+, Cd2+ but also as efficient extractants for Pd 2+, Au3+ and Hg2+. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Loreau J.,Roosevelt University | Sodoga K.,Laboratoire Of Chimie Physique | Sodoga K.,University of Lomé | Lauvergnat D.,Laboratoire Of Chimie Physique | And 3 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

The charge-transfer in low-energy (0.25 to 150eV/amu) H(nl)+He +(1s) collisions is investigated using a quasimolecular approach for the n=2,3 as well as the first two n=4 singlet states. The diabatic potential energy curves of the HeH+ molecular ion are obtained from the adiabatic potential energy curves and the nonadiabatic radial coupling matrix elements using a two-by-two diabatization method, and a time-dependent wave-packet approach is used to calculate the state-to-state cross sections. We find a strong dependence of the charge-transfer cross section on the principal and orbital quantum numbers n and l of the initial or final state. We estimate the effect of the nonadiabatic rotational couplings, which is found to be important even at energies below 1eV/amu. However, the effect is small on the total cross sections at energies below 10eV/amu. We observe that to calculate charge-transfer cross sections in an n manifold, it is only necessary to include states with n′≤n, and we discuss the limitations of our approach as the number of states increases. © 2010 The American Physical Society.

Friedl J.,TUM CREATE | Friedl J.,TU Munich | Al-Oweini R.,Jacobs University Bremen | Herpich M.,TUM CREATE | And 5 more authors.
Electrochimica Acta | Year: 2014

Electrochemical properties of two tri-manganese substituted Keggin-based tungstosilicates [MnII 3(OH)3(H 2O)3(A-α-SiW9O34)] 7- (MnII 3SiW9) and[Mn III 3(OH)3(H2O)3(A- α-SiW9O34)]4- (MnIII 3SiW9) were investigated. The two polyanions are isostructural, the only difference being the oxidation state of the Mn-ions. Despite their structural similarity the electrochemical behaviour is not identical. While it is well established that polyoxometalate (POM) electrochemistry is influenced by interplay between the pH of the electrolyte, the present ions and the pKa values of the complex, this is the first report that the initial oxidation state of the POM has a major influence on the electrochemistry of the transition metal within the molecule. In order to understand the influence of the initial oxidation state extensive electrochemical investigations were performed and the potential dependent adsorption behavior of the molecules on graphite was observed with atomic force microscopy. The reaction mechanism of the two POMs was determined and it was asserted that the divergent redox behavior is caused by a ligand exchange which takes place during the measurement. This influences the adsorption of the molecules on graphite which can be explained by the Born solvation model. Performing controlled potential electrolysis, a stable tri-manganese substituted Keggin ion containing MnIV 3 was obtained electrochemically. © 2014 Elsevier Ltd.

Azougen R.,Laboratoire Of Chimie Physique | EL Guendouzi M.,Laboratoire Of Chimie Physique | Rifai A.,Laboratoire Of Chimie Physique | Faridi J.,Laboratoire Of Chimie Physique
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2010

In this investigation, the ternary aqueous solutions of lithium chloride with alkaline earth metal {yLiCl+(1-y)Y Cl2}(aq) with Y {triple bond, long}Mg2+; Ca2+; and Ba2+ have been studied using the hygrometric method at 298.15 K. The water activities are measured at total molalities from 0.20 mol kg-1 to saturation for different ionic-strength fractions y of LiCl with y = 0.20, 0.50 and 0.80. The obtained data allow the deduction of osmotic coefficients. From these measurements, the mixing ionic parameters θLiY and ψLiY Cl are determined and used to predict the solute activity coefficients in the mixtures. Also, we have completed measurements of water activities from 6 mol kg-1 to saturation of the pure electrolyte solutions of CaCl2(aq) using the hygrometric method. Few studies have extended their measurements to saturation (11.00 mol kg-1 for CaCl2{dot operator}2H2O). These results are compared with those obtained by other techniques. The values of the pure electrolyte and mixing ionic-interaction parameters, which give the best fit of the activity data in binary, ternary solutions and solubility data are tabulated. Thermodynamic characteristics, solubility products Ks p {ring operator} and the standard molar Gibbs energy of formation Δ Gfm 0 of the crystallizing solids are given. The predicted solubility isotherms are compared with the literature data. The behaviour of aqueous electrolyte solutions of alkaline-earth with lithium of chlorides {yLiCl+(1-y)Y Cl2}(aq) with Y {triple bond, long}Mg2+; Ca2+ or Ba2+, is correlated and the results show that the ionic interactions in these solutions are essentially related to the nature of solute combined with the solute LiCl. © 2009.

Belloni J.,Laboratoire Of Chimie Physique | Mostafavi M.,Laboratoire Of Chimie Physique
Actualite Chimique | Year: 2011

Aggregates are compounds constituted of a small number (or nuclearity)n of atoms or molecules. They represent an intermediate state of matter, also named mesoscopic, between both stable states of single atoms (or molecules) and the bulky condensed phase. The aggregates were for long out of reach to experimental observation due to their extremely small size and also totheir short life-time. They tend indeed, depending on the thermodynamicalconditions, to evaporate, sublimate or dissolve, or on the contrary to growtoward the bulky condensed phase. Likewise, theory could not for long describe the aggregates and the complexity of these multi-atomic supra-molecules. However, the very specific properties of aggregates, which are distinct from the bulk, precisely appear for the smallest sizes, between a few tenths of nanometers and a few nanometers. The present knowledge of their behavior is crucial since it governsthe shape, structure, reactivity or stability ofnanoparticles that they form as precursors and that have an increasing rolein nanotechnologies.

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