Facile synthesis of high-surface area platinum-doped ceria for low temperature CO oxidation

International audienceUsing a simple slow decomposition method of nitrate precursors, high-surface area platinum-doped ceria with a crystallite size of 9 nm can be prepared. The catalytic performance of the compound can be tuned by changing the reduction temperature under hydrogen (300°C, 500°C and 700°C). The catalyst treated at 300°C shows the best catalytic performance, being active at room temperature. The materials were analysed using a combination of structural characterization methods (X-ray diffraction (XRD), nitrogen physisorption, high angle annular dark field scanning transmission electron microscopy (HAADF-STEM)), surface sensitive methods (X-ray photoelectron spectroscopy (XPS), H 2-chemisorption and H 2-temperature-programmed reduction (TPR)) and X-ray absorption fluorescence spectroscopy (XAFS). HAADF-STEM and XAFS analysis suggests successful doping of platinum in the ceria lattice. After pretreatment at 300°C, the situation is slightly different. While no defined platinum nanoparticles can be identified on the surface, some platinum is in a reduced state (XPS, H 2-chemisorption)

Multi-method analysis of functionalized single-walled carbon nanotubes for cesium liquid–solid extraction

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Effects of oil on the curvature elastic properties of nonionic surfactant films: Thermodynamics of balanced microemulsions

The free energy of nonionic balanced microemulsions based on nonionic surfactants are analyzed using experimental data from (i) phase behavior, (ii) osmotic compressibility of the balanced microemulsion structure, which is obtained from small angle neutron scattering (SANS) experiments, and (iii) data on interfacial tensions obtained by T. Sottmann and R. Strey [J. Chem. Phys. 106 8606 (1997)]. The balanced microemulsion, where the spontaneous curvature vanishes at equal volumes of water and oil, has a finite swelling with the solvent with a minimum surfactant volume fraction, Phi(*)(S). At higher surfactant concentrations the balanced microemulsion phase having the surfactant volume fraction Phi(S1) coexists with a lamellar phase of volume fraction Phi(S2). Under the constraint of Phi(W)=Phi(O), where Phi(W) and Phi(O) are the water and oil volume fractions, respectively, the free energy density can be written as an expansion in the surfactant concentration. While the phase equilibria only depend on relative values of the expansion coefficients, absolute values can be obtained from compressibility and interfacial tension data. The osmotic compressibility of the surfactant film was measured by SANS through contrast matching water and oil. The phase behavior of nonionic surfactant-water-oil systems depends strongly on the chain length of the oil, when comparing a homologous series from octane to hexadecane using the same surfactant, here being pentaethylene oxide dodecyl ether (C12E5). The three concentrations Phi(*)(S), Phi(S1), and Phi(S2) increase markedly as the chain length of the oil is increased. However, from the analysis of the surface tension data it is concluded that there are no major changes in the bending rigidities as the oil is changed. The data are analyzed within the model free energy densities G/V=a(3)Phi(3)(S)+a(5)Phi(5)(S) and G/V=a Phi(3)(S)(1+b ln Phi(S)). We find that within experimental accuracy, the first of these models provides a quantitatively consistent description of the data. For the second model there is a larger discrepancy between observed and calculated values

High-Surface-Area SiO2-ZrO2 Mixed Oxides as Catalysts for the Friedel-Crafts-Type Alkylation of Arenes with Alcohols and Tandem Cyclopropanation Reactions

International audienceThe catalytic activity of SiO2-ZrO2 mixed oxides was studied for the Friedel-Crafts-alkylation reaction between anisole and benzylic or allylic alcohols. In particular, the influence of Zr content on the catalytic activity was studied. The catalyst with the lowest Zr content (5 mol% ZrO2) showed the highest activity with high selectivity for the alkylated product and good recyclability. We used this catalyst in the reaction of 1-phenyl-1- ethanol with toluene and xylene. We also studied the possibility of a tandem process that involved a Friedel-Crafts alkylation and the subsequent trans-hydrogenation of trans-1,3-diphenyl- 2-propen-1-ol for the synthesis of substituted cyclopropanes

Surface Diels-Alder Reactions as an Effective Method to Synthesize Functional Carbon Materials

International audienceThe post-synthesis chemical modification of various porous carbon materials with unsaturated organic compounds is reported. By this method, amine, alcohol, carboxylate, and sulfonic acid functional groups can be easily incorporated into the materials. Different carbonaceous materials with surface areas ranging from 240 to 1500 m2 g 1 and pore sizes between 3.0 and 7.0 nm have been studied. The resulting materials were analyzed by elemental analysis, nitrogen sorption, FTIR spectroscopy, zeta-potential measurements, thermogravimetric analysis, photoelectron spectroscopy, and small-angle X-ray scattering. These analyses indicated that the degree of functionalization is dependent on the nature of the dienophile (reactivity, steric hindrance) and the porosity of the carbon material. As possible applications, the functionalized carbonaceous materials were studied as catalysts in the Knoevenagel reaction and as adsorbents for Pb2+ from aqueous solution

Enhancement of Oxygen Activation and Mobility in CaTi x Fe 1− x O 3− δ Oxides

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Ionic liquid- and surfactant-controlled crystallization of WO3 films

International audienceWO3 films were obtained via evaporation-induced self-assembly (EISA) using ionic surfactants such as long-chain ionic liquids 1-hexadecyl-3-methyl imidazolium chloride and bromide (C(16)mimCl and C(16)mimBr, respectively) and cetyltrimethylammonium chloride and bromide (CTAC and CTAB, respectively) as additives. Owing to the presence of the ionic surfactants, WO3 films crystallize in a preferred orientation along the a-axis on different substrates, as evidenced by X-ray diffraction. WO3 films with this orientation show improved electrochromic properties when compared to films with a lower degree of crystallographic orientation, prepared in an analogue fashion

In situ generated catalyst: Copper (II) oxide and Copper (I) supported on Ca2Fe2O5 for CO oxidation

International audienc

Porous carbon as catalyst support for CO oxidation: Impact of nitrogen doping

International audienceCarbonaceous materials are abundant, affordable and simple to implement for a wide range of applications. Its utilization as catalyst support for oxidation reactions seems counter intuitive due to the instability of carbonaceous materials under depollution conditions. The current research work demonstrates that the properties of carbon as support can be fine-tuned via the introduction of heteroatoms. The effect of N-doping together with the anchoring of platinum nanoparticles on the catalytic performance is systematically studied. Factors influencing the performance for CO oxidation are elucidated using X-ray scattering, N2 physisorption, transmission electron microscopy, elemental analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, temperature programmed reduction and thermogravimetric analysis. The doping of nitrogen in the carbon framework improves the stability of the carbon support, while adding nitrogen and oxygen improves the stability and performance. Doped carbonaceous materials can be a promising support for low and medium temperature range applications (100-250 ºC)