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The conversion of biomass as a sustainable path to access valuable chemicals and fuels is very attractive for the chemical industry, but catalytic conversions still often rely on the use of noble metals. Sustainability constraints require developing alternative catalysts from abundant and low-cost metals. In this context, NiFe nanoparticles are interesting candidates. In their reduced and supported form, they have been reported to be more active and selective than monometallic Ni in the hydrogenation of the polar functions of organic molecules, and the two metals are very abundant. However, unlike noble metals, Ni and Fe are easily oxidized in ambient conditions, and understanding their transformation in both oxidative and reductive atmospheres is an important though seldom investigated issue to be addressed before their application in catalysis. Three types of NiFe nanoparticles were prepared by an organometallic approach to ensure the formation of ultrasmall nanoparticles (<3.5 nm) with a narrow size distribution, controlled composition and chemical order, while working in mild conditions: Ni2Fe1 and Ni1Fe1, both with a Ni rich core and Fe rich surface, and an alloy with a Ni1Fe9 composition. Supported systems were obtained by the impregnation of silica with a colloidal solution of the preformed nanoparticles. Using advanced characterization techniques, such as wide-angle X-ray scattering (WAXS) and X-ray absorption spectroscopy (XAS) in in situ conditions, this study reports on the evolution of the chemical order and of the oxidation state of the metals upon exposure to air, hydrogen, and/or increasing temperature, all factors that may affect their degree of reduction and subsequent performance in catalysis. We show that if oxidation readily occurs upon exposure to air, the metals can revert to their initial state upon heating in the presence of H2 but with a change in structure and chemical ordering. [ABSTRACT FROM AUTHOR]

Production of hydrogen from a renewable source that is water requires the development of sustainable catalytic processes. This implies, among others, developing efficient catalytic materials from abundant and low-cost resources and investigating their performance, especially in the oxidation of water as this half-reaction is the bottleneck of the water splitting process. For this purpose, NiFe-based nanoparticles with sizes ca. 3–4 nm have been synthesized by an organometallic approach and characterized by complementary techniques (WAXS, TEM, STEM-HAADF, EDX, XPS, and ATR-FTIR). They display a Ni core and a mixed Ni–Fe oxide shell. Once deposited onto FTO electrodes, they have been assessed in the electrocatalytic oxygen evolution reaction under alkaline conditions. Three different Ni/Fe ratios (2/1, 1/1 and 1/9) have been studied in comparison with their monometallic counterparts. The Ni2Fe1 nanocatalyst displayed the lowest overpotential (320 mV at j = 10 mA cm−2) as well as excellent stability over 16 h. [ABSTRACT FROM AUTHOR]

RuNi nanoparticles (NP) were prepared by decomposition of [Ru(η4-C8H12)(η6-C8H10)] and [Ni(η4-C8H12)2] by H2 in the presence of polyvinylpyrrolidone (PVP) at 85 °C using several Ru/Ni ratios. The nanoparticles display a segregated structure in which Ni is on the surface, as ascertained by wide angle X-ray scattering (WAXS). The catalytic activity in the selective hydrogenation of furfural of these RuNi NP was correlated with the Ru content. High selectivity towards the partially hydrogenated product 2-(hydroxymethyl)furan (HF) was found when carrying out the reaction in tetrahydrofuran (THF). A different scenario was found when using a protic polar solvent, 1-propanol. Catalysts displaying Ru on the surface were able to hydrogenate the heteroaromatic ring, while those with Ni on the surface were highly selective towards the partially hydrogenated product. In addition, Ru surfaces were prone to catalyse the acetalization reaction in the presence of the alcoholic solvent, while the addition of Ni supressed this reactivity. Density functional theory (DFT) calculations performed on hydrogenated Ru nanoparticles (Ru55H70) show differences in the adsorption energies of several reagents, products, reaction intermediates, and solvents onto the Ru NP surface, which are in line with the experimental catalytic results. [ABSTRACT FROM AUTHOR]

A hybrid material made of mononuclear organophosphorus polypyridyl ruthenium complexes covalently bonded to ruthenium nanoparticles has been synthesized via a one-pot organometallic procedure and finely characterized. These results open new avenues to access unique hybrid transition metal nanomaterials. [ABSTRACT FROM AUTHOR]

The choice of suitable organometallic precursors, [Re2(C3H5)4] and [Ru(Me-Allyl)2COD] or [Ru(COD)(COT)], allows us to synthesize polyvinylpyrrolidone (PVP) stabilized bimetallic RuRe nanoparticles of ca. 1.3 nm with narrow size dispersity, displaying the hcp crystal structure and to control their chemical order: an alloy or Re rich surface. The structural features of these NPs were determined using complementary characterization techniques (TEM, HRTEM, STEM-HAADF, EDX, WAXS, FT-IR, MAS-NMR and ICP). In particular, surface state investigation based on CO adsorption and oxidation reactions provided useful information of the chemical order in these nanoparticles. The RuRe NPs were obtained as stable colloidal solutions or powders. Surface reactivity studies demonstrated that the alloy type RuRe/PVP NPs show better resistance to oxidation than the ones displaying a Re enriched surface and are more active towards CO dissociation than monometallic Re/PVP NPs as a result of the synergic effect between Ru and Re. Interestingly, the dissociation of CO was not observed with RuRe/PVP NPs displaying a Re enriched surface. Besides the synthetic aspect, this work highlights the crucial influence of the chemical order resulting from the choice of the metal sources in the control of the reactivity of ultra-small metal nanoparticles. [ABSTRACT FROM AUTHOR]

In this work, we describe the synthesis of a new N-heterocyclic carbene (NHC) ligand, derived from a hybrid pyrazole-imidazolium scaffold, namely 1-[2-(3,5-dimethylpyrazol-1-yl)ethyl]-3-((S)-1-phenylethyl)-3H-imidazol-2-ylidene (L). This ligand has been used as a stabilizer for the organometallic synthesis of palladium(0) nanoparticles (Pd NPs). L presents a better stabilizing effect than its pre-carbenic HLCl counterpart, allowing the formation of isolated Pd NPs while HLCl yields aggregated ones. Additionally, molecular Pd(ii) coordination compounds of L and HLCl were synthesized and characterized to better understand the coordination modes of these ligands. Both molecular and colloidal Pd systems have been further tested in catalytic C–C coupling processes. Three different types of reactions have been observed depending on the catalytic system: (i) the Suzuki–Miyaura reaction takes place with Pd molecular complexes; (ii) a secondary reaction, the dehalogenation of the substrate, is always detected and (iii) the C–C homocoupling between two molecules of bromoarenes is observed with colloidal catalysts. [ABSTRACT FROM AUTHOR]

Enhancement of the thermoelectric properties of bismuth due to size reduction has prompted a large body of studies and recent interest in the nanochemistry of this material. The size control at the nanometer scale is complicated because of bismuth's low melting point and little known surface chemistry. We report herein an efficient synthetic method producing bismuth nanoparticles (Bi NPs) of sizes below 10 nm, and of rhombohedral structure based on transmission electron microscopy (TEM) and wide angle X-ray scattering (WAXS) analysis. The nature and dynamics of the ligands at their surface have been investigated by infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) spectroscopy. We demonstrate that alkynyl ligands, seldom used in nanochemistry, efficiently coordinate at the surface and afford stable Bi NPs that can be easily purified, leading to powders with high bismuth payload which can be redispersed into stable colloidal solutions. [ABSTRACT FROM AUTHOR]

Ultra-small monodisperse rhenium nanoparticles (Re NPs; ca. 1.0-1.2 nm) were easily prepared by reducing the organometallic complex [Re2(C3H5)4] under a dihydrogen atmosphere under mild reaction conditions (3 bar H2;120 °C). The particles can be stabilized by a ligand, hexadecylamine, or a polymer, polyvinylpyrrolidone and accommodate surface hydrides. [ABSTRACT FROM AUTHOR]

Production of hydrogen from a renewable source that is water requires the development of sustainable catalytic processes. This implies, among others, developing efficient catalytic materials from abundant and low-cost resources and investigating their performance, especially in the oxidation of water as this half-reaction is the bottleneck of the water splitting process. For this purpose, NiFe-based nanoparticles with sizes ca . 3-4 nm have been synthesized by an organometallic approach and characterized by complementary techniques (WAXS, TEM, STEM-HAADF, EDX, XPS, and ATR-FTIR). They display a Ni core and a mixed Ni-Fe oxide shell. Once deposited onto FTO electrodes, they have been assessed in the electrocatalytic oxygen evolution reaction under alkaline conditions. Three different Ni/Fe ratios (2/1, 1/1 and 1/9) have been studied in comparison with their monometallic counterparts. The Ni2Fe1 nanocatalyst displayed the lowest overpotential (320 mV at j = 10 mA cm -2 ) as well as excellent stability over 16 h.

The choice of suitable organometallic precursors, [Re 2 (C 3 H 5 ) 4 ] and [Ru(Me-Allyl) 2 COD] or [Ru(COD)(COT)], allows us to synthesize polyvinylpyrrolidone (PVP) stabilized bimetallic RuRe nanoparticles of ca. 1.3 nm with narrow size dispersity, displaying the hcp crystal structure and to control their chemical order: an alloy or Re rich surface. The structural features of these NPs were determined using complementary characterization techniques (TEM, HRTEM, STEM-HAADF, EDX, WAXS, FT-IR, MAS-NMR and ICP). In particular, surface state investigation based on CO adsorption and oxidation reactions provided useful information of the chemical order in these nanoparticles. The RuRe NPs were obtained as stable colloidal solutions or powders. Surface reactivity studies demonstrated that the alloy type RuRe/PVP NPs show better resistance to oxidation than the ones displaying a Re enriched surface and are more active towards CO dissociation than monometallic Re/PVP NPs as a result of the synergic effect between Ru and Re. Interestingly, the dissociation of CO was not observed with RuRe/PVP NPs displaying a Re enriched surface. Besides the synthetic aspect, this work highlights the crucial influence of the chemical order resulting from the choice of the metal sources in the control of the reactivity of ultra-small metal nanoparticles.

In this work, we describe the synthesis of a new N-heterocyclic carbene (NHC) ligand, derived from a hybrid pyrazole-imidazolium scaffold, namely 1-[2-(3,5-dimethylpyrazol-1-yl)ethyl]-3-((S)-1-phenylethyl)-3H-imidazol-2-ylidene (L). This ligand has been used as a stabilizer for the organometallic synthesis of palladium(0) nanoparticles (Pd NPs). L presents a better stabilizing effect than its pre-carbenic HLCl counterpart, allowing the formation of isolated Pd NPs while HLCl yields aggregated ones. Additionally, molecular Pd(ii) coordination compounds of L and HLCl were synthesized and characterized to better understand the coordination modes of these ligands. Both molecular and colloidal Pd systems have been further tested in catalytic C-C coupling processes. Three different types of reactions have been observed depending on the catalytic system: (i) the Suzuki-Miyaura reaction takes place with Pd molecular complexes; (ii) a secondary reaction, the dehalogenation of the substrate, is always detected and (iii) the C-C homocoupling between two molecules of bromoarenes is observed with colloidal catalysts.