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Ru/CNF catalysts of different Ru nanoparticle (NP) sizes (0.9-2.7 nm) were assessed for their performance in continuous supercritical water gasification (SCWG) of glycerol. A structure sensitivity of Ru was demonstrated, with high initial turnover frequencies (TOF) for Ru NPs smaller than 1.2 nm. Deactivation happens essentially through: 1) coking, which occurs more readily at low Ru surface densities and is limited to nanometric layers, and 2) sintering, which led to final NP sizes ranging from 2 to 3 nm independent of the catalyst loading (1 to 30 wt% Ru). A correlation between TOF and the density of surface Ru atoms was found, with an optimal surface density (0.4-0.7 atomRu,sfc nm−2) resulting in high initial and good steady-state TOFs, allowing longer lifetimes through the delay of coke formation. CNF as a support enables high metal loadings with optimal performance, which could help in decreasing the volume of high-pressure vessels and hence the cost of SCWG plants, making this technology even more attractive.

In hydrothermal valorization of black liquor (BL) from the Kraft process, the separation of inorganic salts is pivotal to prevent them from fouling downstream equipment such as reactors and for the cost-efficient recycling of salts into pulp cooking chemicals. In this work, the phase behavior of the inorganic salts present in BL was studied in supercritical water and the conditions for the separation from BL were optimized. A high-pressure differential scanning calorimetry study indicated the concomitant precipitation of salts and the formation of a second salt-rich liquid-like phase. The potassium-to-sodium ratio was found to strongly impact the phase behavior of the salt mixture. Potassium was found to prevent salt precipitation and to lead to the formation of a second liquid-like phase alone. At K/(K + Na) ≥ 0.4, a steady salt separation could be achieved, enabling the continuous extraction of up to 96% of the salts in a concentrated brine effluent.

The realization of metal–semiconductor contacts plays a significant role in ultrascaled integrated circuits. Here, we establish a low-temperature molecular approach for the conformal deposition of a 20 nm Co-rich layer on Si (100) wafers by reaction in solution of Co2(CO)8 with SiH4. Postannealing at 850 °C under vacuum (∼10–5 mbar) yields a crystalline CoSi2 film with a lower surface roughness (Rrms = 5.3 nm) by comparison with the conventional physical method; this layer exhibiting a metallic conductive behavior (ohmic behavior) with a low resistivity (ρ = 11.6 μΩ cm) according to four-point probe measurement. This approach is applicable to trench-structured wafers, showing the conformal layer deposition on 3D structures and showcasing the potential of this approach in modern transistor technology.

Hyperpolarization of metabolites by dissolution dynamic nuclear polarization (D-DNP) for MRI applications often requires fast and efficient removal of the radicals (polarizing agents). Ordered mesoporous SBA-15 silica materials containing homogeneously dispersed radicals, referred to as HYperPolarizing SOlids (HYPSOs), enable high polarization – P(1H) = 50% at 1.2 K – and straightforward separation of the polarizing HYPSO material from the hyperpolarized solution by filtration. However, the one-dimensional tubular pores of SBA-15 type materials are not ideal for nuclear spin diffusion, which may limit efficient polarization. Here, we develop a generation of hyperpolarizing solids based on a SBA-16 structure with a network of pores interconnected in three dimensions, which allows a significant increase of polarization, i.e. P(1H) = 63% at 1.2 K. This result illustrates how one can improve materials by combining a control of the incorporation of radicals with a better design of the porous network structures., Chemical Science, 7 (11), ISSN:2041-6520, ISSN:2041-6539

Tailoring the physical features and the porous network architecture of silica-based hyperpolarizing solids containing TEMPO radicals, known as HYPSO (hybrid polarizing solids), enabled unprecedented performance of dissolution dynamic nuclear polarization (d-DNP). High polarization values up to P(1H)=99 % were reached for samples impregnated with a mixture of H2O/D2O and loaded in a 6.7 T polarizer at temperatures around 1.2 K. These HYPSO materials combine the best performance of homogeneous DNP formulations with the advantages of solid polarizing matrices, which provide hyperpolarized solutions free of any—potentially toxic—additives (radicals and glass-forming agents). The hyperpolarized solutions can be expelled from the porous solids, filtered, and rapidly transferred either to a nuclear magnetic resonance (NMR) spectrometer or to a magnetic resonance imaging (MRI) system.

Improvement of the catalytic performance of supported nanoparticles (NP) is an intense area or research, which involves modification of many different parameters on a nanoparticle (such as variation of particle size), support (e.g. its reducibility) and metal–support interactions. Here, we focus on the latter and show that the introduction of passivating groups (–OSi(Me) 2R with R = Me or Bu ) at the interface between the support surface (silica) and RuNPs increases the rate of the reaction on RuNPs (per mole of surface Ru atoms) by a factor 5–6 compared to silica-supported RuNPs, whose surface is exposed to silanols. Chemisorption , IR spectroscopy and temperature-programmed desorption tests suggest that the rate increase likely originates from the difference in interaction between CO and RuNPs, which is influenced by the modification of the support surface functionality. It is also possible that the change in catalyst activity could be due to a modified electronic state of nanoparticles and/or their morphology.

Hyperpolarization of NMR-active nuclei is key to gather high quality spectra of rare species and insensitive isotopes. We have recently established that silica-based materials containing regularly distributed nitroxyl radicals connected to the silica matrix by flexible linkers can serve as promising polarization matrices for dynamic nuclear polarization (DNP). Here we investigate the influence of the linker on the efficiency of the polarization. The materials were fully characterized and exhibit high surface areas and narrow pore size distributions with a tunable amount of phenyl azide groups over a broad range of concentrations. The phenyl azide groups can be easily functionalized via a two-step procedure with 4-carboxy-2,2,6,6-tetramethyl-1-oxylpiperidine (TEMPO) to give polarizing matrices with controllable radical content. The DNP efficiency was found to be similar as in materials with flexible linkers, both for magic angle spinning at 105 K and dissolution DNP at 4 K.

Silica supported nickel nanoparticles of 2.2 ± 0.4 nm diameter were selectively doped with tin by surface organometallic chemistry while keeping the particle size nearly constant. The catalysts with various tin contents were doped and characterized by TEM, XRD and H2 chemisorption. In contrast to what is found at high temperature (≥973 K), dry reforming tests performed at 773 K and successive TPO and TEM analysis showed that tin neither influences the catalyst deactivation rate nor prevents coke formation, present in the form of encapsulating carbon. The nickel dopant does not influence either the selectivity, ruled by reverse water gas shift Thermodynamics, but was shown to have a 3–4-fold decrease of intrinsic activity of the available surface nickel, thus indicating that Sn has a negative effect on adjacent Ni atoms.

Platinum nanoparticles are efficiently prepared by the reaction of Pt molecular precursors with trihydrogeno(octyl)silane, which acts both as a reducing agent and as a stabilizer. Various Pt(0) and Pt(II) organometallic precursors can be used to yield narrowly dispersed nanoparticles with a mean Pt core diameter of 1.1 to 1.6 nm. NMR Diffusion Ordered SpectroscopY (DOSY) proved to be a very helpful method to both demonstrate the anchoring of the octylsilane chains to the nanoparticle core and measure its diameter. The very mild reaction conditions pave the way for fast, reliable and safe bench top nanoparticles synthesis.

The influence of nickel particle size in the range of 1.6–7.3 nm on catalyst performance in low temperature CO 2 reforming of methane reaction has been investigated using well-defined catalysts based on a neutral silica support. XAS and XPS studies indicated a reduction degree greater than 90%. The intrinsic Ni/SiO 2 performances were found to be independent of nickel particle size in dry reforming at 773 K using a CH 4 /CO 2 ratio of 1.3 at 1 atm, both at an early stage and in steady state conditions. The H 2 /CO ratio was also found to be structure in sensitive but is controlled by thermodynamics through the faster reverse water gas shift reaction.

Preparing highly active and stable non-noble-metal-based dry reforming catalysts remains a challenge today. In this context, supported nickel nanoparticles with sizes of 1.3 ± 0.2 and 2.1 ± 0.2 nm were synthesized on silica and ceria, respectively, via a two-step colloidal approach. First, 2-nm nickel-silicide colloids were synthesized from Ni(COD)(2) and octylsilane at low temperature; they were subsequently dispersed onto supports prior to reduction under H(2). The resulting catalysts display high activity in dry reforming compared to their analogues prepared using conventional approaches, ceria providing greatly improved catalyst stability.

Dry-reforming catalysts were prepared by supporting Ni nanoparticles (2–3 nm) on La-doped silica. These materials display higher activity and stability in low-temperature dry reforming (773 K) than Ni/SiO2 or Ni/La2O3. The La-doped silica-supported catalysts were found to have exclusively lanthanum silicate at their surface rather than La2O3 and/or SiO2. While an increasing amount of La was found to favor both CO2 adsorption capacity and strength, it also influenced the hydrogen adsorption strength on nickel particles significantly, as evidenced by H2 temperature-programmed desorption analysis. Finally, CH4 temperature-programmed reduction analysis revealed that the CH4 cracking threshold temperature varies in the order: Nibulk

A bifunctional catalyst for the sorbent-enhanced steam methane reforming (SE-SMR) reaction was derived from a hydrotalcite-based precursor synthesized via a coprecipitation technique. The material contained both the Ni reforming catalyst and the Ca-based CO2 sorbent and was characterized using X-ray diffraction, H2 chemisorption, N2 physisorption, transmission electron microscopy, and temperature-programmed reduction. Reduction of the calcined hydrotalcite converted the (Al:Ca:Mg:Ni)Ox mixed oxide into nickel and CaO particles supported on an (Al:Mg)Ox matrix with a surface area of 54 m2·g–1. The high CO2 absorption capacity and its stability with carbonation cycles was attributed to the high dispersion of CaO on the porous and thermally stable (Al:Mg)Ox network, whereas for naturally occurring limestone, a rapid decay in the CO2 absorption capacity was observed. Under SE-SMR conditions, the recorded mole fraction of hydrogen in the effluent stream was 99 vol % (dry and without inert component); that is, ...

Desilication of the medium-pore ferrierite zeolite in sodium hydroxide solutions was conducted to modify the porous structure and to create structural defects, resulting in enhanced accessibility and ultimately improved catalytic performance. Commercial H-ferrierite (Si/Al = 29) with the characteristic plate-like morphology was used as starting material. The attack by NaOH induces deaggregation, exfoliation, fracture, and ultimately perforation of the ferrierite crystals, resulting in mesoporosity of combined inter- and intracrystalline nature. The parent and treated samples were characterized by ICP-OES, XRD, N2 adsorption, SEM, TEM, 27Al and 29Si MAS-NMR, FTIR, and NH3-TPD. Optimization of the treatment conditions (NaOH concentration, temperature, and time) is required to introduce substantial mesoporosity without significantly altering the micropore structure due to excessive Si leaching. Compared to other frameworks (e.g. MFI, MTW, MOR, and BEA), FER requires harsher conditions to extract silicon leading to mesoporosity. Under optimal conditions, the mesopore surface area of the NaOH-treated ferrierite increased by a factor of 3–4 with respect to the parent zeolite, while mostly preserving the native crystallinity and acidity. The ability of NaOH to induce porosity changes in FER largely exceeds conventional dealumination post-treatments. The benefit of the introduced porosity was demonstrated in the catalytic pyrolysis of low-density polyethylene.

International audience; Hyperpolarization by dynamic nuclear polarization relies on the microwave irradiation of paramagnetic radicals dispersed in molecular glasses to enhance the nuclear magnetic resonance (NMR) signals of target molecules. However, magnetic or chemical interactions between the radicals and the target molecules can lead to attenuation of the NMR signal through paramagnetic quenching and/or radical decomposition. Here we describe polarizing materials incorporating nitroxide radicals within the walls of the solids to minimize interactions between the radicals and the solute. These materials can hyperpolarize pure pyruvic acid, a particularly important substrate of clinical interest, while nitroxide radicals cannot be used, even when incorporated in the pores of silica, because of reactions between pyruvic acid and the radicals. The properties of these materials can be engineered by tuning the composition of the wall by introducing organic functionalities.

Herein, we report the preparation of small and narrowly distributed (2.1 ± 0.5 nm) Ag nanoparticles supported on passivated silica, where the surface OH groups are replaced by OSiMe3 functionalities. This synthetic method involves the grafting of silver(I) bis(trimethylsilyl)amide ([AgN(SiMe3)2]4) on silica partially dehydroxylated at 700 °C, followed by a thermal treatment of the grafted complex under H2. The catalytic performance of this material was investigated in the semi-hydrogenation of propyne and 1-hexyne and compared with that of 2.0 ± 0.3 nm Ag nanoparticles supported on silica. Whilst surface passivation slightly decreases the activity in both reactions (by a factor 2–3), probably as a result of the decreased alkyne adsorption properties or the presence of less accessible active sites on the passivated support, the AgNP@SiO2 catalysts demonstrate a remarkable selectivity for the production of alkenes.

Silica supported iridium and rhodium nanoparticles were prepared via surface organometallic chemistry (SOMC). Following the synthesis and characterization of organometallic molecular precursors [(COD)MOSiOR](2) (M = Ir or Rh; R = Me or Si(OtBu)(3)), their controlled grafting on partially dehydroxylated silica yields isolated dinuclear surface species, as determined by H-1 and C-13 solid state NMR as well as infrared transmission spectroscopies and elemental analysis. The decomposition under hydrogen of the well-defined surface species affords a narrow size distribution and a homogeneous spatial repartition of small M(0) particles despite a high metal density (1.2 +/- 0.3 nm and 1.4 +/- 0.3 nm for Ir and Rh, respectively). A combination of transmission electronic microscopy and gas chemisorption provides the H-2 and CO adsorption stoichiometries on the metal surface, which are highly dependent on the precursor and the preparation route, indicating the necessity to control each step and the danger to determine particle size solely from chemisorption studies for small iridium and rhodium supported particles. (C) 2014 Elsevier Inc. All rights reserved.

Osmium(cyclooctadiene)(cyclooctatetraene) is used as a molecular precursor to prepare small and narrowly distributed silica supported nanoparticles upon a mild treatment under H2 (1.1 ± 0.3 nm, ca. 90 atoms). Static volumetric chemisorption combined with HAADF-STEM shows that Os nanoparticles adsorb 1.7 ± 0.1 H and 1.4 ± 0.1 CO per surface atom. These particles present high activity in the hydrogenolysis of alkanes via a dimetallacyclopentane mechanism.

The gas-phase partial hydrogenation of propyne was investigated over supported Ag nanoparticles (2–20 nm in diameter) prepared by using different deposition methods, activation conditions, loadings, and carriers. The excellent selectivities to propene attained over the catalysts, exceeding 90 %, are independent of the particle size but the activity is maximal over approximately 4.5 nm Ag particles. Certain kinetic fingerprints of Ag, such as the positive dependence on the alkyne pressure, the relatively low reaction order in H2, and the low apparent activation energy, deviate from those of conventional hydrogenation metals such as Pd and Ni, questioning the applicability of the classical Horiuti–Polanyi scheme. Periodic dispersion-corrected density functional theory (DFT-D) calculations and microkinetic analysis demonstrate the occurrence of an associative mechanism, which features the activation of H2 on the adsorbed propyne at structural step sites. By using the atomistic Wulff model, the number of B5 sites available on the Ag nanoparticles was estimated to be maximal in the size range of 3.5–4.7 nm. The rate of propene production correlates with the density of B5 sites, which suggests that the latter are potential active centers for the reaction. This alternative pathway broadens the mechanistic diversity of hydrogenation reactions over metal surfaces and opens new directions for understanding metals that do not readily activate H2.

+PDE; We describe here an original methodology related to the "build-the-bottle-around-the-ship" approach yielding a highly ordered silica matrix containing regularly distributed Pt nanoparticles (NPs) located inside the silica walls, Pt@{walls}SiO(2). The starting colloidal solution of crystalline Pt nanoparticles was obtained from Pt(dba)(2) (dba = dibenzylidene acetone) and 3-chloropropylsilane. The resulting nanoparticles (diameter: 2.0 +/- 0.4 nm determined by HRTEM) resulted hydrophilic. The NPs present in the THF colloidal solution were incorporated inside the walls of a highly ordered 2D hexagonal mesoporous silica matrix via sol-gel process using a templating route with tetraethylorthosilicate, TEOS, as the silica source, and block copolymer (EthyleneOxide)(20)(PropyleneOxide)(70)(EthyleneOxide)(20) (Pluronic P123) as the structure-directing agent. Low-temperature calcination of the crude material at 593 K led to the final solid Pt@{walls}SiO(2). Characterization by IR, HRTEM, BF-STEM and HAADF-STEM, SAXS, WAXS, XRD, XPS, H(2) chemisorption, etc. of Pt@{walls}SiO(2) confirmed the 2D hexagonal structuration and high mesoporosity (870 m(2)/g) of the material as well as the presence of stable 2-nm-sized crystalline Pt(0) NPs embedded inside the walls of the silica matrix. The material displayed no tendency to NPs sintering or leaching (Pt loading 0.3 wt.%) during its preparation. Pt@{walls}SiO(2) was found to be a stable, selective and highly active hydrogenation catalyst. The catalytic performances in propene hydrogenation were tested under chemical 'regime conditions in a tubular flow reactor (278 K, propene/H(2)/He = 20/16/1.09 cm(3)/min, P(tot) = 1 bar) and were found superior to those of an homologous solid containing Pt NPs along its pore channels Pt@{pores}SiO(2) and to those of a classical industrial catalysts Pt/Al(2)O(3), (TOF = 2.3 s(-1) vs. TOF = 0.90 and 0.92 s(-1), respectively, calculated per surface platinum atoms). Pt@{walls}SiO(2) also catalyzes fast and selective styrene hydrogenation. A material containing by design Pt NPs both in its walls and in its pores, Pt@{walls + pores}SiO(2), is also described. (C) 2011 Elsevier Inc. All rights reserved.

The facile and selective synthesis of small crystalline Pt(3)Sn alloy nanoparticles was performed at room temperature under H(2), using a colloidal approach without the use of extra-stabilizing ligands. The Pt(3)Sn alloy was found to be obtained spontaneously as the unique phase regardless of the number of tin equivalents introduced.

The race for performance of integrated circuits is nowadays facing a downscale limitation. To overpass this nanoscale limit, modern transistors with complex geometries have flourished, allowing higher performance and energy efficiency. Accompanying this breakthrough, challenges toward high-performance devices have emerged on each significant step, such as the inhomogeneous coverage issue and thermal induced short circuit issue of metal silicide formation. In this respect, we developed a two-step organometallic approach for nickel silicide formation under near-ambient temperature. Transmission electron and atomic force microscopy show the formation of a homogeneous and conformal layer of NiSix on pristine silicon surface. Post-treatment decreases the carbon content to a level similar to what is found for the original wafer (similar to 6%). X-ray photoelectron spectroscopy also reveals an increasing ratio of Si content in the layer after annealing, which is shown to be NiSi2 according to X-ray absorption spectroscopy investigation on a Si nanoparticle model. I-V characteristic fitting reveals that this NiSi2 layer exhibits a competitive Schottky barrier height of 0.41 eV and series resistance of 8.5 Omega thus opening an alternative low-temperature route for metal silicide formation on advanced devices.