Grup de Dendrímers i Polígons Moleculars

Palladium nanoparticles peripherally functionalized with “RuCl2(p-cymene)” (NP2), “RhCl(cod)” (NP3) and “PdCl(3-2-MeC3H4)” (NP4) units show catalytic activity in C C coupling reactions, hydrogenation and hydrovinylation processes. We report for the first time an example of a catalytic precursor for the hydrovinylation/C C coupling sequential process by using the two catalytic centres displayed by NP4, the Pd core and the PdCl(3-2-MeC3H4) moieties.

A facile strategy has been explored for loading noble metals onto the surface of ferrite nanoparticles with the assistance of phosphine-functionalized linkers. Palladium loading is shown to occur with participation of both the phosphine function and the surface hydroxyl groups. Hybrid nanoparticles containing simultaneously Pd and Au (or Rh) are obtained by successive loading of metals. Similarly, ferrite nanoparticles decorated with Pd, Au, and Rh have also been formed by using the same strategy. The catalytic properties of the new nanoparticles are evidenced in processes such as reduction of 4-nitrophenol or hydrogenation of styrene. Besides, the sequential process involving a cross-coupling reaction followed by reduction of 1-nitrobiphenyl has been successfully achieved by employing Pd/Au decorated nanoferrite particles.

We report a method to improve the thermal stability, up to 900 degrees C, of bare-metal (naked) gold nanoparticles supported on top of SiO2 and SrTiO3 substrates via ligand-assisted pinning. This approach leads to monodisperse naked gold nanoparticles without significant sintering after thermal annealing in air at 900 degrees C. The ligand-assisted pinning mechanism is described.

A synthesis of organometallic functionalized thiol-protected palladium nanoparticles (Pd NPs) is presented. The first step of the procedure consists of forming starting Pd NPs protected with two different ligands. The shorter one, hexanethiolate, is introduced to provide solubility to the system in organic solvents, and the larger is the alkane thiolate HS(CH2)(11)OOCC6H4PPh2 (L), equipped with a terminal free phosphine group. Reaction of the latter nanoparticles, NP1, with appropriate organometallic derivatives, permitted the isolation of soluble Pd NPs displaying at the periphery the metal units PdCl(eta(3)-2-MeC3H4) (NP2), IrCl(cod) (NP3), RuCl2(p-cymene) (NP4), RhCl(cod) (NP5), RhCl(CO) (NP6), and Rh(cod)(+)(NP7). The palladium nanopartides were examined using NMR, FTIR, HRTEM, TGA, and XPS.

Click cycloaddition reaction between azidodecanethiol and 4-ethynyl pyridine gave the thiol ligand L. Partial ligand exchange reaction between 1-hexanethiol-protected gold nanoparticles and L produced soluble gold nanoparticles (NP1) containing both linkers: the short 1-hexanethiol provides solubility in common solvents while L contains the free pyridine ligand. NP1 reacted with the complexes [RuCl2(p-cymene)](2) and [RhCl(cod)](2) (cod - cycloocta-1,5-diene) to form Au NPs peripherally functionalized with organometallic Ru (NP2) and Rh (NP3) moieties, respectively. The gold nanoparticles were characterized using NMR, FT-IR, HRTEM, and TGA.

The reaction of the new ditopic thiol-phosphine compound HS(CH2)11OOCC6H4PPh2 (L) with an excess of dodecanethiol-protected gold nanoparticles gave the asymmetric gold complex [CH3(CH2)11SAuPPh2C6H4COO(CH2)11SH] (4), but no phosphine-protected gold nanoparticles were formed. However, by blocking the phosphine function in L with metal fragments, we have been able to produce gold nanoparticles functionalised with AuCl- and cluster [Fe2(CO)7Au] units on the surface by the method of ligand-place exchange reaction.

Propene oxidation to propene oxide (PO) was performed with N₂O in the temperature range of 473–673 K using TiO₂-supported Au and Au–Cu alloy nanoparticles synthesized from pre-formed thiol-capped nanoparticles of controlled composition and size. Catalysts were activated by calcination at different temperatures in the range 573–873 K and characterized by HRTEM, XPS, and TPR. Among a series of catalysts with different Au/Cu ratio and metal loading, the Au₁Cu₃/TiO₂ with 1.2 wt% exhibited the best catalytic performance for epoxidation, both in terms of propene conversion rate and selectivity towards PO (0.25 mol  POg_M^-1h^-1 at 573 K). The highest TOF was obtained over a catalyst calcined at 673 K. At this calcination temperature, HRTEM revealed a large perimeter interface between the nanoparticles and the support, which was accompanied by an intense TPR hydrogen uptake at low temperature. At increasing calcination temperature, the surface of Au–Cu alloy nanoparticles was progressively decorated with oxidized Cu species, which were detrimental for epoxidation and favored allylic oxidation products. Isolation effects and control of the extent of Cu oxidation by Au in the alloy nanoparticles as well as the perimeter interface between Au–Cu alloy nanoparticles and TiO₂ are imagined to play pivotal roles in the epoxidation of propene.

Catalytically active gold nanoparticle films have been prepared from core-shell nanoparticles by plasma-activation and characterized by high resolution transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Methane can be selectively oxidized into formic acid with an O2–H2 mixture in a catalytic wall reactor functionalized with plasma-activated gold nanoparticle films containing well-defined Au particles of about 3.5 nm in diameter. No catalytic activity was recorded over gold nanoparticle films prepared by thermal decomposition of core-shell nanoparticles due to particle agglomeration.