Hybrid polarizing solids for pure hyperpolarized liquids through dissolution dynamic nuclear polarization

Hyperpolarization of substrates for magnetic resonance spectroscopy (MRS) and imaging (MRI) by dissolution dynamic nuclear polarization (D-DNP) usually involves saturating the ESR transitions of polarizing agents (PAs; e.g., persistent radicals embedded in frozen glassy matrices). This approach has shown enormous potential to achieve greatly enhanced nuclear spin polarization, but the presence of PAs and/or glassing agents in the sample after dissolution can raise concerns for in vivo MRI applications, such as perturbing molecular interactions, and may induce the erosion of hyperpolarization in spectroscopy and MRI. We show that D-DNP can be performed efficiently with hybrid polarizing solids (HYPSOs) with 2,2,6,6-tetramethyl-piperidine-1-oxyl radicals incorporated in a mesostructured silica material and homogeneously distributed along its pore channels. The powder is wetted with a solution containing molecules of interest (for example, metabolites for MRS or MRI) to fill the pore channels (incipient wetness impregnation), and DNP is performed at low temperatures in a very efficient manner. This approach allows high polarization without the need for glass-forming agents and is applicable to a broad range of substrates, including peptides and metabolites. During dissolution, HYPSO is physically retained by simple filtration in the cryostat of the DNP polarizer, and a pure hyperpolarized solution is collected within a few seconds. The resulting solution contains the pure substrate, is free from any paramagnetic or other pollutants, and is ready for in vivo infusion

Réalités industrielles et perspectives de développement des membranes d'ultrafiltration de 3

Les techniques d'ultrafiltration et de microfiltration tangentielle utilisant des membranes minérales carbosep constituent un exemple typique des retombées technologiques des céramiques nucléaires microporeuses. Les propriétés de ces membranes et leur introduction dans divers domaines des industries agroalimentaires et biotechnologiques seront examinées

Pd/Rh catalysts for the abatement of car emissions pollutants

SSCI-VIDE+CARE+JGR:SGI:LRE:AGFInternational audience1. IntroductionPresently, catalysts are widely employed in the abatement of pollutants from automobiles, being the three-way catalyst (TWC) the most common system used in the gasoline powered vehicles, due to its capacity to achieve the elimination of CO, HC and NO simultaneously. Pt/Rh containing catalysts dominated the automobile exhaust converter market for many years. However, Pd is more abundant and cheap, and has therefore drawn much attention. In addition, the Pd catalysts developed demonstrated significantly improved light-off and NOx conversion activities compared to the commercial Pt/Rh TWCs [1]. Generally, the particle size has a great effect in the catalytic activity of Pd in the TWC, showing smaller particles a higher activity, especially for the oxidation of CO and HC; probably due to a higher presence of Pd (I) species [2]. In this work, we apply a novel colloidal procedure in the catalysts preparation of a Pd/Rh TWC, procedure that has proven to be successful in order to obtain very small metal particles (1-2 nm) when preparing Ni [3] or Pt [4] catalysts.2. ExperimentalPd, Rh and four Pd/Rh catalysts with different impregnation order were prepared by impregnation of metal-Si colloids, mixing Pd and/or Rh organometallic complexes in THF with octylsilane as a stabilizing agent, in the presence of H2; using a standard TWC washcoat. More details about the procedure followed can be found elsewhere [3]. After impregnation, the catalyst was stabilized at 650 °C for 2 h under a flow of N2 with 10% of H2O. Light off tests were carried out using 40 mg of catalyst and SiC as inert in order to reach a GHSV = 52.000h-1 with a total flow of 10 l h-1. The feed gas composition was 4% CO2, 3% H2O, 0.86 % O2, 3000 ppm C3H6, 2300 ppm H2, 1500 ppm NO, 700 ppm CO, using He as balance. 3. Results and discussionMetal particle size was analyzed using the TEM technique, showing all the catalysts metal particles sizes around 1 nm both for Pd and Rh. No differences in particle size were observed depending in the impregnation order or comparing monometallic with bimetallic catalysts. The actual metal content was analyzed by ICP, Table 1.Table 1: Main characterization and catalytic results.Catalyst%Pd%RhT50 (°C) C3H6-CO2T50 (°C) CO-CO2T50 (°C) NO-N2Pd/Washcoat0.51 - 313184-454304Rh/Washcoat- 0.06 297228-412313Pd/Rh/Washcoat0.70 0.05 296173-434299Rh/Pd/Washcoat0.76 0.06 304177-451299Pd-Rh/Washcoat0.67 0.09 301177-447306Pd/Washcoat+Rh/Washcoat0.27 0.05 310183-457314Great differences were observed depending on the metal, as can be observed in Figure 1. At 100 ºC a decrease of the concentration of H2 and NO for the Pd catalyst was obtained, probably due to the concurrence of the H2 SCR reaction, while in the case of the Rh catalyst no catalytic activity was observed until 200 °C. This different behaviour is probably due to the higher H2 adsorption capacity of Pd compared to Rh, what increases the reactivity of this molecule. At about 150 °C it can be observed a decrease in the O2 and CO concentration also for the Pd catalyst, while the NO concentration rises to its initial value. This is probably due to the beginning of the oxidation of CO towards CO2 and also to the oxidation of H2 towards H2O, being this reaction competitive with the H2 SCR. In the case of the Rh catalyst, the oxidation of both CO and H2 did not start until reaching a temperature of 200-220 °C, showing therefore a lower activity in these oxidative reactions. In addition, two different peaks were obtained in the CO conversion for the Pd catalyst, while only one peak with a slight shoulder was observed for the Rh one, what yields a bigger range of temperature in which there are conversion of CO for the first catalyst. This is due to the higher activity of Pd in the CO oxidation at low temperature, and also to the higher activity of Rh in the reforming of C3H6 at medium temperatures (350-450 °C), what yields CO and H2 as products, as can be observed in the increase of the concentration of these compounds at such temperatures.Figure 1: Concentration (dark colors) and Conversion (light colors) vs Temp.: a) Pd/Washcoat b) Rh/Washcoat.Moreover, obtained results showed that the impregnation order had an important influence on the behaviour of the catalysts, showing the catalyst where Rh was impregnated in the last place the conversion and concentration profiles more similar to the Rh catalyst. In Table 1 it can be observed the temperature needed to reach 50% of conversion in the C3H6-CO2, CO-CO2 and NO-N2 reactions for each one of the catalysts prepared. Pd/Rh and Rh/Pd showed the better catalytic behavior, needing lower temperatures to reach the 50% of conversion of NO towards N2 and also the highest temperature range to reach at least a 50% of conversion of CO. In addition, Pd/Rh was the catalyst with the lowest T50 in the conversion of C3H6 to CO2.4. ConclusionsThis new colloidal procedure has shown to be useful in order to obtain Pd and Rh particles of size around 1 nm in a TWC catalyst. A higher activity at low temperature in the H2 SCR and CO oxidation was observed for the Pd/Washcoat catalyst compared with the Rh/Washcoat catalyst. Catalyst prepared impregnating in the first place Rh and after that Pd showed the higher catalytic activity in the three main reactions in which are involved the TWC

Preparation and characterization – including in situ Small Angle X-Ray Scattering – of gas chromatographic capillary columns with mesoporous silica thin films as stationary phases

International audienceIn this study the preparation of various mesoporous silica thin films as new stationary phases for gas chromatography (GC) columns is presented. The synthesis was performed inside capillaries via a sol gel process using a templating route. The as-obtained columns were found to be highly efficient for the fast separation of light n-alkanes (C1-C5) mixture; these columns exhibiting a normalized retention 30 times higher than that of a commercially available silica column used as standard. A particular effort was directed towards the characterization of the stationary phase physical features: thin film inspection by Scanning Electron Microscopy and, for the first time to our knowledge, in situ SAXS characterization using synchrotron radiation were used to study the impact of the pore-network structuration on the GC properties. Worm-like, cubic and hexagonal phases were observed for specific preparation conditions. Unexpectedly, the normalized retention relative to film thickness appeared higher with disordering of the pores network. (C) 2015 Elsevier B.V. All rights reserved

Nanostructured equimolar ceria-praseodymia for NOx-assisted soot oxidation: Insight into Pr dominance over Pt nanoparticles and metal–support interaction

This work compares the catalytic activity of nanostructured ceria-praseodymia impregnated with Pt nanoparticles stabilized by n-octylsilane (Pt/Ce50Pr50-NP), with pure ceria nanoparticles (Ce-NP), ceria-praseodymia (Ce50Pr50-NP) and Pt on ceria (Pt/Ce-NP). The idea behind these structures stems from the fact that both Pt/ceria and Ce-Pr mixed oxide are effective towards CO, NO and soot oxidations, as well as for the NOx-assisted soot oxidation. The oxide supports have been prepared via a hydrothermal synthesis. Catalytic activity tests have shown the effectiveness of Ce50Pr50-NP towards the NOx-assisted soot oxidation. The intrinsic activity of this material is even higher than the Pt/Ce-NP counterpart. This finding seems related to the adsorption of NO2 onto ceria-praseodymia. The addition of Pt on the Ce50Pr50-NP surface appears unnecessary as the effect of Pr on the catalytic activity prevails. The samples have also been thermally aged and their catalytic performances have been compared. A smaller decrease in activity has been observed for Ce50Pr50-NP, compared to Ce-NP, and it has been linked to the material's persistent adsorptive properties. The deposited Pt nanoparticles on the surface of Ce50Pr50-NP, however, have suffered from sintering after the thermal aging, and therefore both aged Pt/Ce50Pr50-NP and Ce50Pr50-NP have comparable catalytic performance

Selective and regular localization of accessible Pt nanoparticles inside the walls of an ordered silica: Application as a highly active and well-defined heterogeneous catalyst for propene and styrene hydrogenation reactions

+PDEWe 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