Catalysis to discriminate single atoms from subnanometric ruthenium particles in ultra-high loading catalysts

We report a procedure for preparing ulta-high metal loading (10-20 % w/w Ru) Ru@C60 nanostructured catalysts comprising exclusively Ru single atoms. We show that by changing the Ru/C60 ratio and the nature of the solvent used during the synthesis, it is possible to increase the Ru loading up to 50% w/w, and to produce hetero-structures containing subnanometric Ru nanoparticles. Several techniques such as high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy – high angle annular dark field (STEM-HAADF), Raman spectroscopy, wideangle X-ray scattering (WAXS), extended X-ray absorption fine structure (EXAFS) and X-ray photoelectron spectroscopy (XPS) together with theoretical calculations were used to characterize these materials. At such high metal loading, the distinction between Ru single atoms and clusters is not trivial, even with this combination of techniques. We evaluated the catalytic properties of these materials for the hydrogenation of nitrobenzene and 2,3-dimethyl-2-butene. The catalysts containing only Ru single atoms are much less active for these reactions than the ones containing clusters. For nitrobenzene hydrogenation, this is because electro-deficient Ru single atoms and few atom Run clusters are not performant for H2 activation compared to larger clusters (n ≥ 13), as shown by density functional theory (DFT) calculations. For the more crowded substrate 2,3-dimethyl-2-butene, DFT calculations have shown that this is due to steric hindrance. These simple tests can thus been used to distinguish samples containing metallic sub-nanometer nanoparticles. These novel catalysts are also extremely active for the hydrogenation of -substituted 2,3-dimethyl-2-butene

Construction de catalyseurs supportés par auto-assemblage

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Selectivity shifts in hydrogenation of cinnamaldehyde on electron-deficient ruthenium nanoparticles

International audienceRuthenium fulleride nanospheres were produced and decorated with small (<1.5 nm) ruthenium nanoparticles. These materials, which present a significant charge transfer from ruthenium to the electron acceptor C60 fullerene, were tested in the hydrogenation of cinnamaldehyde. In alcoholic solvents, very large amounts (≈90%) of acetals were formed, pointing out the high acidity of the Ru sites. The addition of a weak base and the use of methanol as a solvent allow to reach high activity and selectivity toward cinnamyl alcohol, whereas the use of an aprotic and apolar solvent decreases the activity and yields mainly hydrocinnamaldehyde. Density functional theory calculations show that this selectivity shift is not correlated to a specific precoordination of cinnamaldehyde on the ruthenium nanoparticles

Synergistic effect between carbon nanomaterials and ZnO for photocatalytic water decontamination

ZnO synthesized by chemical vapor deposition (CVD) was combined with different carbon nanomaterials namely nanotubes, nanofibers, nanodiamonds, fullerene and graphene. The materials were characterized by physical adsorption of nitrogen, diffuse reflectance, UV-Vis and photoluminescence (PL) spectroscopies, transmission electron microscopy and temperature programmed desorption. The photocatalytic efficiency of the resulting carbon/ZnO composites was evaluated for phenol degradation under simulated solar light irradiation. In general, the carbon materials enhance the efficiency of ZnO, and the composite containing nitrogen-doped carbon nanotubes (N-CNT/ZnO) showed the highest photocatalytic activity. An increase of 100% in the apparent first order rate constant for phenol degradation was achieved when using N-CNT/ZnO instead of bare ZnO. PL spectra confirmed the presence of efficient electron transfer between the carbon phase and the ZnO with a maximum quenching of ZnO PL emission in the presence of N-CNT. Both ZnO and N-CNT/ZnO show high stability after four reuses

Alloyed Pt 3 M (M = Co, Ni) nanoparticles supported on S- and N-doped carbon nanotubes for the oxygen reduction reaction

International audienceSulfur- (S-CNT) and nitrogen-doped (N-CNT) carbon nanotubes have been produced by catalytic chemical vapor deposition (c-CVD) and were subject to an annealing treatment. These CNTs were used as supports for small (≈2 nm) Pt3M (M = Co or Ni) alloyed nanoparticles that have a very homogeneous size distribution (in spite of the high metal loading of ≈40 wt % Pt), using an ionic liquid as a stabilizer. The electrochemical surface area, the activity for the oxygen reduction reaction and the amount of H2O2 generated during the oxygen reduction reaction (ORR) have been evaluated in a rotating ring disk electrode experiment. The Pt3M/N-CNT catalysts revealed excellent electrochemical properties compared to a commercial Pt3Co/Vulcan XC-72 catalyst. The nature of the carbon support plays a key role in determining the properties of the metal nanoparticles, on the preparation of the catalytic layer, and on the electrocatalytic performance in the ORR. On N-CNT supports, the specific activity followed the expected order Pt3Co > Pt3Ni, whereas on the annealed N-CNT support, the order was reversed