Retention and diffusion of radioactive and toxic species on cementitious systems: Main outcome of the CEBAMA project

Cement-based materials are key components in radioactive waste repository barrier systems. To improve the available knowledge base, the European CEBAMA (Cement-based materials) project aimed to provide insight on general processes and phenomena that can be easily transferred to different applications. A bottom up approach was used to study radionuclide retention by cementitious materials, encompassing both individual cement mineral phases and hardened cement pastes. Solubility experiments were conducted with Be, Mo and Se under high pH conditions to provide realistic solubility limits and radionuclide speciation schemes as a prerequisite for meaningful adsorption studies. A number of retention mechanisms were addressed including adsorption, solid solution formation and precipitation of radionuclides within new solid phases formed during cement hydration and evolution. Sorption/desorption experiments were carried out on several anionic radionuclides and/or toxic elements which have received less attention to date, namely: Be, Mo, Tc, I, Se, Cl, Ra and 14C. Solid solution formation between radionuclides in a range of oxidation states (Se, I and Mo) with the main aqueous components (OH−, SO4 −2, Cl−) of cementitious systems on AFm phases were also investigated

Catalytic wet air oxidation of succinic acid over monometallic and bimetallic gold based catalysts: Influence of the preparation method

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Catalytic wet air oxidation of succinic acid over monometallic gold based catalysts: influence of the preparation method.

internationa

Catalytic wet air oxidation of succinic acid over monometallic and bimetallic gold based catalysts: Influence of the preparation method

SSCI-VIDES+EAU+MBE:CDEInternational audienceDifferent methods for the preparation of gold catalysts (mono and bimetallic) were used - the modified deposition-precipitation (MDP), the deposition-precipitation by ammonia (DPA) and the colloidal method (CM). The catalytic performances of all samples were evaluated in the catalytic wet air oxidation (CWAO) of succinic acid under mild conditions (190 degrees C, 50 bar total pressure). The results showed that the preparation procedure and the addition of a second metal (Pt or Ru) clearly influence the catalytic activity and selectivity, depending on the size of the gold particles and the nature of the second metal

NO reduction by CO over gold catalysts based on ceria supports prepared by mechanochemical activation modified by Me3+ (Me=Al or lanthanides): Effect of water in the feed gas

Cataloged from PDF version of article.The reduction of NO by CO was studied over gold catalysts supported on ceria modified by Me3+ ions (Me = Al, La, Sm, Gd and Yb). The ceria supports were prepared by mechanochemical activation. The samples were characterized using XRD, TPR, XPS and Raman spectroscopy. According to the XPS data the concentration of the oxidized gold species was higher than that of metallic gold in the fresh samples modified by lanthanides. On the fresh samples modified by Al only a small part of metallic gold existed in oxidized state. After the catalytic test, only metallic gold was found on the lanthanide-containing catalysts while on the M-modified catalyst a small amount of oxidized Au species in addition to metallic Au was detected. No substantial differences in the average particle sizes of gold, the lattice parameters and the average size of ceria particles were observed. The nature of the modifier and the applied method of ceria supports preparation and gold deposition determined most likely the differences observed in the Raman and TPR data, as well as the catalytic activity results. The catalytic tests were performed under two different conditions: (i) in the presence of H-2 in the gas feed and (ii) adding also water to the gas feed. The lowest activity was observed over the Al-containing catalyst under dry feed, which correlates with the TPR results. The addition of water to the feed led to a significant improvement of the NO and CO conversions over all of the samples studied. At 200 degrees C, Yb-containing gold catalyst exhibited the highest NO and CO conversions. Very promising results for the selectivity toward N-2 were achieved using the lanthanides as dopants. In contrast to the gold supported on Al-doped ceria, no NH3 formation was observed within the whole temperature interval up to 400 degrees C over gold catalysts supported on ceria modified by La, Sm, Gd or Yb. (C) 2009 Elsevier B.V. All rights reserved

Gold based mono and bimetallic catalysts in the catalytic wet air oxidation of arganic pollutants.

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Catalyseurs à base d’or (mono et bimétalliques Au-Pt) pour l’oxydation catalytique en voie humide de composés organiques

SSCI-VIDE+CARE:CDFA+MBE:CDSInternational audienceNon

Catalyseurs à base d’or (mono et bimétalliques Au-Pt) pour l’oxydation catalytique en voie humide de composés organiques

SSCI-VIDE+CARE:CDFA+MBE:CDSInternational audienceNon

Mechanistic investigations of the promoting role of Rh on the NSR performance of NOx storage BaO-based catalysts

To determine the promoting effect of Rh on the overall NOx storage and reduction (NSR) performance, the studies in the current work were directed toward investigating the storage and release ability over Rh NOx storage BaO-based catalysts compared to Pt. In terms of the metal surface dispersion and the ability of the noble metals to release oxygen at lower temperatures, the synthesized catalysts were characterized by means of dynamic CO chemisorption (RT) and N2O dissociation (RI - 773 K). The NOx storage capacity and the thermal stability of the NOx adsorbed species formed on the surface were analyzed via NOx storage tests and temperature programmed desorption (TPD) without and in the presence of CO2 and H2O. In addition, experiments with lean and rich cycling were conducted at 473,573 and 673 K. The results from the N2O dissociation experiments showed the superior ability of Rh/Al and Rh/Ba/Al catalysts compared to Pt toward O-2 release from the catalytic surface at lower temperatures. In this work, we show that the presence of Rh into the BaO/gamma-Al2O3 system has a considerable effect on the spill-over process of NOx to the precious metal, controlling the subsequent desorption of NOx to occur at lower temperatures in comparison with that of the Pt catalysts. It is suggested a mechanism of NOx desorption where the lower temperature of O-2 release from the surface of Rh catalysts could leave a significant number of noble metal sites accessible for adsorption. Thus this could facilitate the rate of spill-over of NOx from the storage site (the surface sites on gamma-Al2O3 and those on BaO) to the noble metal and their desorption at lower temperatures. The limited NOx storage ability of the Rh-based BaO/gamma-Al2O3 catalysts under lean-burn conditions was found to originate from both low NO oxidation activity and NOx reduction activity, while the main limiting factor for the low NSR performance of the Pt-based catalysts was the limited regeneration ability during rich period

A novel Cry9Aa with increased toxicity for Spodoptera exigua (Hübner)

Cry9Aa, produced by Bacillus thuringiensis is reported to be not active against Spodoptera exigua (beet armyworm). In this study we have cloned a new cry9Aa5 gene encoding a protoxin with increased activity against S. exigua as compared to Cry9Aa1. When aligned to Cry9Aa1, four amino acid substitutions in domain I and one substitution in the C-terminal protein extension of Cry9Aa5 were identified. Toxicity of Cry9Aa5, produced in recombinant Escherichia coli was assessed and compared to the activity of Cry9Aa1, produced under the same conditions