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The synthesis of Rh nanoparticles has been performed through an organometallic approach starting from the tris(allyl) rhodium complex, Rh(η3-C3H5)3, as precursor and using an alcohol as both a solvent and a stabilizer, under mild reaction conditions (room temperature; 3 bar H2). The influence of the alcohol used, among methanol, propanol or heptanol, on the morphological and structural characteristics as well as on the magnetic and electrocatalytic properties of the obtained Rh nanoparticles has been investigated. Assemblies of Rh nanoparticles of various sizes have been observed depending on the alkyl chain length of the alcohol used. A noticeable effect of the nanostructured character of these Rh nanoparticles is the appearance of a ferromagnetic ordering at room temperature due to a modified electronic structure. Magnetic moments per atom were determined as follows: 0.099, 0.073 and 0.036 µB for methanol, heptanol and propanol, respectively. The electrochemical evaluation of these Rh nanoparticles on the oxygen reduction reaction (ORR) showed that the electroactivity depends on the chain length of the alcohol; thus, Rh-heptanol system displayed the highest electroactivity for ORR. [ABSTRACT FROM AUTHOR]

Review: 74 refs. [ABSTRACT FROM AUTHOR]

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]

Composition (metal or metal oxide core and organic coating), size, shape and structure are the main parameters governing the properties of nano-objects. Driven by their huge potential for application in fields as diverse as catalysis, energy, environment, electronics and medicine much research effort has been dedicated to the control of these parameters over the past 30 years. Namely, the use of concepts and techniques of molecular chemistry has provided remarkable advances in the growth of well-defined nanostructures by pointing out the key roles played by both the metal precursors and stabilizing agents (polymers, dendrimers, ionic liquids, ligands, etc .) during the three main steps of the formation of nanostructures: release of metal atoms, nucleation and growth. It is now currently admitted that interaction between the precursor and stabilizing agent may generate intermediate complexes in the reacting medium which may change the course of the reaction. Also, coordination of the ligand on the growing seeds is recognized as an important factor influencing the growth of nanostructures. Finally, coordination of the ligand at the surface of nanostructures may induce a change in their physical and chemical properties by tuning electronic density and steric hindrance at their surface. To illustrate these points, this review will focus on metal nanostructures synthesized in organic solutions from molecular metal complexes as metal sources and stabilized by coating ligands, short chain molecules with headgroups able to coordinate onto the metal surface. Recent advances will be described highlighting the incidence of coordination chemistry through a selection of relevant examples from the literature. [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]

Abstract: Rhodium composite nanomaterials were synthesized by an innovating process called dry impregnation in a fluidized bed. It consists in spraying an aqueous colloidal suspension of rhodium on silica porous particles. The use of this precursor solution containing preformed nanoparticles avoids calcination/activation step. Different composite nanomaterials were prepared displaying various metal loadings. The operating conditions were tuned to modify τ s, the solvent vapour saturation rate value, in order to influence the deposit location: either uniform on the whole silica particles or at the particles surface like a coating. τ s is defined as the ratio between solvent content in the bed atmosphere and the maximum solvent content. The obtained samples were investigated in catalytic hydrogenation of aromatic compounds under very mild conditions. Their catalytic performances were compared to those of the original colloidal suspension in one hand and of a similar catalyst prepared through wet impregnation in another hand. Interesting activity and selectivity were observed. This illustrates the interest of the dry impregnation method: this way allows an easy control of the metal loading as well as of the metal loading location in the support particles. Moreover, the support particle size and morphology are preserved. [Copyright &y& Elsevier]

The synthesis of metal nanoparticles dispersed inside the grains of a porous inorganic support was carried out by "dry impregnation" in a fluidized bed. The principle of this technique consists in the spraying of a solution containing a metal source into a hot fluidized bed of porous particles. The metal source can be of different nature such as metal salts, organometallic precursors or colloidal solutions. The experimental results obtained from iron oxide deposition on a porous silica gel as support, constitute the core of this article but others results concerning the deposition of rhodium from a colloidal suspension containing preformed rhodium nanoparticles are also described. More precisely, this study aims to understand the effect of the bed temperature during the impregnation step, the initial particle porosity and the calcination operating protocol on the metallic nanoparticles dispersion and location in the silica porous particles. The so-obtained products were characterized by various techniques in order to determine their morphology, their surface properties and the dispersion of the nanoparticles inside the support. The results showed that, under the chosen operating conditions, the deposit efficiency is close to 100% and the competition between the drying rate, depending on the process-related variables, and the capillary penetration rate, depending on the physicochemical related variables, controls the deposit location. A quasi uniform deposit inside the support particles is observed for soft drying. The metal nanoparticles size is controlled by the pore mean diameter of the support as well as the calcination operating protocol. [ABSTRACT FROM AUTHOR]

The synthesis of catalytic or not composite materials by dry impregnation in fluidized bed is described. This process can be carried out under mild conditions from solutions of organometallic precursors or colloidal solutions of preformed nanoparticles giving rise to reproducible metallic nanoparticles containing composite materials with a high reproducibility. The adequate choice of the reaction conditions makes possible to deposit uniformly the metal precursor within the porous matrix or on the support surface. When the ratio between the drying time and the capillary penetration time ( tsec/ tcap) is higher than 10, the impregnation under soft drying conditions leads to a homogeneous deposit inside the pores of the particles of support. The efficiency of the metal deposition is close to 100%, and the size of the formed metal nanoparticles is controlled by the pores diameter. Finally, some of the presented composite materials have been tested as catalysts: iron-based materials were used in carbon-nanotubes synthesis, while Pd and Rh composite materials have been investigated in hydrogenation reactions. [ABSTRACT FROM AUTHOR]

Nanomaterials based on Pd nanoparticles supported on Vulcan carbon (XC-72R) were prepared by the organometallic approach in one-pot and mild conditions (3 bar hydrogen and room temperature) using Pd(dba)2 (bis (dibenzylideneacetone) palladium (0)) as metal source and hexadecylamine (HDA) as stabilizer. High-resolution transmission electron microscopy (HR-TEM) evidenced the presence of well-dispersed Pd nanoparticles of ca. 4.5 nm mean size onto the carbon support (Pd/HDA/C). Scanning and transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) allowed to determine the chemical composition of the nanomaterials. When the Pd/HDA/C nanomaterial was submitted to heating treatment (ht) at 400 °C under air (referred as Pd/HDA/C@air-ht), X-ray photoelectron spectroscopy (XPS) and HR-TEM/STEM-EELS analyses suggested the presence of interactions between PdO and Pd(0) as a result of the formation of Pd@PdO core–shell nanoparticles. The highest oxidation current magnitude during methanol oxidation reaction is ascribed to the heat-treated material, linked with a better electron and mass transfer processes at the electrode interface. This can be attributed to electronic interactions at the core–shell formed, which might promote different redox processes at the electrode interface during CH3OH deprotonation in the alkaline electrolyte. [ABSTRACT FROM AUTHOR]

A series of ferrocenylphosphine-stabilized rhodium nanoparticles has been prepared in one pot from the organometallic [Rh(η3-C3H5)3] precursor. This complex has been decomposed by hydrogen treatment (3 bar) in dichloromethane in the presence of five different ferrocene-based phosphine ligands. Very small rhodium nanoparticles in the size range of 1.1–1.7 nm have been obtained. These nanoparticles have shown activity in a model catalytic reaction, namely the hydrogenation of styrene. These results evidence that the metal surface is not blocked despite the steric bulk of the stabilizing ligands. Moreover, certain selectivity has been observed depending on the ligand employed. To the best of our knowledge, such a type of compound has not yet been used for stabilizing metal nanoparticles and our findings highlight the interest to do so. [ABSTRACT FROM AUTHOR]

A porous Ru nanomaterial exhibits high electrocatalytic performance and excellent durability for the hydrogen evolution reaction (HER) under both acidic and neutral conditions. It displays a low overpotential of 83 mV at a current density of 10 mA cm−2 and an excellent durability up to 12 h in 0.5 M H2SO4. [ABSTRACT FROM AUTHOR]

Review: 313 refs. [ABSTRACT FROM AUTHOR]

The solution synthesis of rhodium nanoparticles (Rh NPs) was achieved from the organometallic complex [Rh(η3-C3H5)3] under mild reaction conditions in the presence of a polymer (PVP), a monophosphine (PPh3) and a diphosphine (dppb) as a stabilizer, leading to very small Rh NPs of 2.2, 1.3 and 1.7 nm mean size, with PVP, PPh3 and dppb, respectively. The surface properties of these nanoparticles were compared using a model catalysis reaction namely, hydrogenation of cyclohexene, first under colloidal conditions and then under supported conditions after their immobilization onto an amino functionalized silica-coated magnetite support. PVP-stabilized Rh NPs were the most active catalyst whatever the catalytic conditions as a result of a strong coordination of the phosphine ligands at the metal surface that blocks some surface atoms even after several recycles of the supported nanocatalysts and limit the reactivity of the metallic surface. [ABSTRACT FROM AUTHOR]

The synthesis and catalytic activity of long-chain NHC-stabilized RuNPs are presented. Full characterization of these novel nanostructures including surface state studies show that the ligand influences the number and the location of Ru active sites which impacts the NP catalytic activity, especially in hydrogenation reactions. The high stability and versatility of these nanosystems make them successful catalysts for both oxidation and hydrogenation reactions that can even be performed successively in a one pot-fashion. [ABSTRACT FROM AUTHOR]

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]

The betaine adduct of N-heterocyclic carbene and carbodiimide (ICy·(p-tol)NCN) was found to be a very efficient ligand to prepare very small (1–1.3 nm) ruthenium nanoparticles (RuNPs). The coordination of the ligand on the metal surface takes place through the carbodiimide moiety. The resulting RuNPs led to decarbonylation of THF and showed size selectivity for styrene hydrogenation. [ABSTRACT FROM AUTHOR]

The reactivity of ruthenium nanoparticles stabilized by 4-(3-phenylpropyl)pyridine in hydrogen transfer and hydrogenation processes was monitored by NMR spectroscopy. Unsaturated substrates such as styrene, 4-vinylpyridine and 4-phenyl-but-3-en-2-one were used as model molecules to investigate the surface properties of nanoparticles by a combination of NMR studies. Interestingly, the hydrides present at the metallic surface after nanoparticles synthesis are selectively transferred to vinylic groups without reducing the aromatic rings, under dihydrogen-free atmosphere. DOSY and NOE NMR experiments permitted to propose a way of interaction of the organic compounds at the metallic surface. In particular, the coordination of the substrate could be evidenced for 4-vinylpyridine and 4-ethylpyridine but not for styrene derivatives. Graphical Abstract: Curved double arrows represent magnetization exchanges. Straight arrows represent adsorption/desorption phenomena. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: The organometallic synthesis of ruthenium nanoparticles stabilized by water-soluble alkyl sulfonated diphosphines as ligands is described for the first time. After isolation, the so-obtained nanoparticles could be easily dispersed into water giving rise to stable aqueous colloidal solutions without precipitation over the course of several months. The catalytic behaviour of these aqueous colloidal solutions has been investigated in the hydrogenation of unsaturated substrates (tetradecene, styrene and acetophenone) in biphasic liquid–liquid conditions, showing interesting results in terms of reactivity. Interestingly, small structural differences in the backbone of the diphosphine ligands influence the catalytic activity of these nanocatalysts. In addition, preliminary tests of recycling showed promising results with neither loss of activity or significant precipitation. [Copyright &y& Elsevier]

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]

Structural and spectroscopic properties of tetranuclear ruthenium hydrido clusters, and to a less extent, of hexanuclear ruthenium hydrido clusters, are investigated theoretically. Some of these (H)nRuk(L)m (k = 4, 6) clusters were experimentally synthesized and characterized. Non-existing structures are also considered in order to examine the role of ligands on their structure, vibrational spectra and 1HNMR chemical shifts. The calculated properties are found in very good agreement with experimental data, when available. Beyond the intrinsic interest elicited by transition metal clusters, these compounds are also considered in this paper as relevant to diamagnetic ruthenium nanoparticles as well as building blocks of hcp surfaces, which is the ruthenium nanoparticle lattice. On the basis of the very good agreement between experiments and theory, the structural and spectroscopic properties of several model clusters are also predicted in order to bring additional data which may help to analyze the spectral signature of ruthenium nanoparticles. A particular emphasis is put on 1H NMR, which is of high practical importance for characterizing the presence of hydrides in ruthenium clusters and nanoparticles. Several topics are discussed: the structural preference of surface hydrides for terminal-, edge-bridging or face-capping coordination modes, hydrides adsorption energies, the possible presence of interstitial hydrogen atoms, the dependence of 1H chemical shifts on ligands and on electron counting. [ABSTRACT FROM AUTHOR]

Abstract: The production of supported catalysts by impregnation method of porous supports can be carried out in a fluidized bed. This technique allows to obtain, in only one apparatus, catalysts which by the traditional way must successively undergo the stages of impregnation, filtration, drying and calcination/activation. This paper deals with the results of experiments related to the manufacture of traditional catalysts and new generation catalysts containing various metals (nickel, manganese, copper, palladium) deposited on a porous support such as alumina or silica gel. Moreover, it was shown that the reproducible synthesis of metallic nanoparticles of size, composition and controlled surface quality could be carried out under mild conditions with organometallic precursors. The principle of this technique consists in the spraying of a solution containing a metallic precursor into a hot fluidised bed of porous fine particles as chosen support. The adequate choice of operating conditions makes possible a uniform deposit of the metal precursor inside the porous matrix. After the impregnation step, the decomposition of the metallic precursor and metal activation can be operated in the same reactor. For organometallic complexes the decomposition/activation is achieved at low temperature (T <80 °C) under a reactive atmosphere (H2/N2 mixture) giving then rise to the synthesis of metal nanoparticles with controlled size and composition. Feasibility studies and optimisation of the operating conditions have been carried out, solid characterization and catalytic tests have been conducted to validate the process. In the case of asymmetric catalysts, Pd nanoparticles associated to cinchonidine as an asymmetric ligand inside silica particles have been prepared by this process for the ethyl pyruvate hydrogenation. [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]