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Here we report on the organometallic synthesis of polyvinylpyrrolidone (PVP)-stabilized palladium-rhodium nanostructures that display high electrochemical properties when used as carbon-supported electrodes (Pd x Rh 1-x -PVP/C) for methanol oxidation reaction (MOR). These nanostructures were synthesized by hydrogenation of the tris(dibenzylideneacetone)dipalladium(0) (Pd 2 (dba) 3) and tris(allyl) rhodium (Rh(η3-C 3 H 5) 3) complexes, in tetrahydrofuran (THF) under mild reaction conditions (room temperature and 3 bar H 2) and in the presence of PVP as stabilizer. The influence of methanol concentration (0.5, 1.0 and 2.0 M) as well as different scan rates (5–100 mV s−1) was evaluated to determine changes in the stability and catalytic activity. The organometallic approach and the use of PVP for the preparation of PdRh electrode materials promoted the formation of highly dispersed nanostructures, that led to a remarkably enhanced methanol electro-oxidation in alkaline medium. This high catalytic behavior can reasonably arise from a synergistic effect between Pd and Rh metals as, under the applied conditions, Rh is expected to enhance the Pd ability to oxidize methanol to CO 2 (oxophilic character) as well as the catalyst stability. From all the evaluated electrode materials, Pd 8 Rh 2 -PVP/C electrode showed the highest mass activity at high methanol concentration (2.0 M) and low scan rate (10 mV s−1). This catalyst showed a performance up to 26 times higher than that of Pd-PVP/C and interestingly an electroactivity superior to that of previously reported PdRh catalysts. [Display omitted] • This synthesis led to the formation of well-dispersed nanostructures of size <5 nm. • Pd 8 Rh 2 -PVP/C showed an enhanced performance, up to 26 times higher than Pd-PVP/C. • CVs shifts in the oxidation peak potential towards (-) values as Rh amount increases. • Oxophilic character in the PdRh alloys is favored at low Rh quantities. [ABSTRACT FROM AUTHOR]

Highlights: [•] Catalysts based on carbon-supported Pd nanoparticles (NPs) were prepared. [•] Catalysts activity was investigated in the hydrogenation of anthracene. [•] High conversions and selectivities towards the hydrogenated products were achieved. [•] No cracking or ring-opening products were obtained. [•] Reaction pathway for anthracene hydrogenation is proposed. [Copyright &y& Elsevier]

Supported Pd nanocatalysts were prepared by deposition of Pd nanoparticles (NPs) onto spherical mesoporous carbon beads (MB) functionalized by thermal or acidic treatement. The Pd NPs were synthesized by decomposition of [Pd 2 (dba) 3 ] (dba: dibenzylideneacetone) under dihydrogen either directly on the carbon supports without stabilizer leading to naked Pd NPs (Pd/MB series) or in solution in the presence of a stabilizer (polymer (PVP series) or triphenylphosphine (TPP series)) to obtain stable colloidal solutions that were further used to impregnate the carbon materials to have carbon-deposited Pd NPs. The NPs deposited on carbon displayed a Pd loading from 0.5 to 14.8 wt.% and were characterized by different techniques (nitrogen physisorption at 77 K, H 2 -chemissorption and TPD, XRD, XPS and HRTEM). Their catalytic performance in deoxygenation of oleic acid was evaluated in batch and flow reaction conditions. Flow conditions led to superior results compared to batch. No aromatic compounds were detected as side products, but in the case of the Pd/MB series, octadecanol and octadecane were significantly formed suggesting the involvement of a deoxygenation mechanism in which the hydrocarbons were produced via both decarbonylation/decarboxylation and dehydration steps. Further experiments carried out in H 2 /N 2 mixture or in pure N 2 highlighted the key role of hydrogen. For a N 2 /H 2 of 2.5:1 the dehydration route was crossing out and even no traces of octadecanol nor octadecane were detected. Then, complete removal of H 2 produced heptadecene in a high excess compared to heptadecane (almost 7–1) thus suggesting the decarbonylation/decarboxylation steps as the main route. ICP-OES measurements indicated no leaching of palladium and simple washing of catalysts with mesitylene allowed recycling without any change in conversion or product distribution. [ABSTRACT FROM AUTHOR]

Abstract: Both (Ni, Pt) and bimetallic (Ni x Pt; x =1, 2, 3) nanoparticles have been synthesized by hydrogenation of Ni(cod)2 ad Pt2(dba)3 in the presence of a weak coordinating ligand, hexadecylamine (CH3(CH2)15NH2, HDA). These nanostructures were characterized by different techniques (Fourier Transform-Infrared Spectroscopy (FT-IR), High-Resolution Transmission Electron Microscopy (HRTEM)), and were evaluated as Hydrogen Evolution Reaction electrocatalysts in 0.5M sulfuric acid. The effects of varying the platinum amount during the synthesis were systematically studied by Cyclic Voltammetry (CV), polarization measurements and electrochemical impedance spectroscopy (EIS) techniques. HRTEM shows that the bimetallic nanostructures display a different morphology compared to that observed for pure Ni and Pt ones. The process of hydrogen adsorption–desorption in the as-prepared electrodes seems to occur in (110) and (100) facets. It was found that the increase in the activity for the HER is due to an increased electrochemical active surface area (ECSA) and/or stabilization in the case of elemental electrode materials; and to the effect of Pt amount in the case of the Ni–Pt nanostructures (synergistic effect leads to lower overpotential). It has been established that the main pathway for the HER is Volmer–Heyrovsky. [Copyright &y& Elsevier]

Abstract: This study reports an efficient method for the preparation of well-dispersed ruthenium nanoparticles of controlled size loaded into micelle-templated silica (MTS). This method is based on an organometallic approach consisting in mild decomposition of Ru(COD)(COT) (COD=η4-cycloocta-1,5-diene; COT=η6-cycloocta-1,3,5-triene) embedded inside mesostructured porous silica. The role assigned to the regular channels of MTS is to host and stabilize the metal nanoparticles. Different procedures of precursor decomposition, variation of metal loadings and of MTS pore sizes were examined in order to identify the crucial parameters governing the location, size and dispersion of the nanoparticles. The composite materials were characterized using elemental analysis, thermal gravimetric analysis, X-ray diffraction, nitrogen sorption at 77K and TEM. The advantage of this new procedure lies in the absence of particles sintering due to the Ru reduction at room temperature and the stabilization of the nanoparticles by suitable pore size of the host. [Copyright &y& Elsevier]