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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.

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.

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

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.