Competitive Adsorption of NOx and Ozone on the Catalyst Surface of Ozone Converters

International audienceFour catalysts—1%Pd-2%Mn/γ-Al2O3, 1%Pd/γ-Al2O3, 2%Mn/γ-Al2O3 and γ-Al2O3—were synthesized via a sol–gel method and characterized using various techniques to evaluate their physicochemical, textural, surface and acidic properties. They were used in the catalytic transformation of ozone and nitrogen oxides using in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. Different consecutive gas sequences were followed to unravel the poisoning role of nitrogen oxides and the possible reactivation by ozone. It has been proven that on palladium and manganese-based catalysts, the inhibition effect of nitrogen oxides was due to the formation of monodentate nitrites, monodentate, bidentate and bridged nitrates, which are difficult to desorb and decompose into gaseous NOx, either by oxidation or by thermal treatment. Interestingly, monodentate nitrites could be eliminated if the catalyst went through a co-adsorption of NOx and ozone prior to exposure in clean ozone flow. This transformation could be the reason why the catalytic conversion of ozone could return to its original value before the poison effect of nitrogen oxide

Qualification des émissions d'aérosols radioactifs liées à l'utilisation d'un générateur de technétium en service de médecine nucléaire

National audienceThe objective of this work is to characterize the emission of radioactive particles of 99mTc (technetium-99, a metastable gamma emitter of 6 h half-life) for lung marking in the environment of a nuclear medicine department. We studied the leakage of radioactive particles from the generating system during a lung scan test. This possible source of air contamination has been little studied and a specifically adapted survey methodology remains to be developed. To measure the leakage of radioactive particles from the generator, we designed a transportable test enclosure permitting one to collect and sample particles with a known accuracy, a low background level and the capability of recording short time events. Here, we present the characterization operations for this system and results we obtained with patients. The results show that radioactivity released in the air by the generator leakage is superior to that deposited in the patients' lungs by inhalation, that is, respectively, 5.7% and 3.8% of the total radioactivity initially introduced into the generator. © 2012 EDP Sciences.L’objectif de ce travail est de caractériser l’émission de particules radioactives de 99mTc (technétium-99 métastable émetteur gamma de demi-vie 6 h) servant au marquage pulmonaire dans l’environnement d’un service de médecine nucléaire. Nous avons étudié les fuites du système générateur de particules radioactives lors d’un examen de scintigraphie pulmonaire. Cette éventuelle source de contamination ambiante a été peu étudiée et une méthodologie de surveillance spécifiquement adaptée reste à développer. Pour mesurer les fuites des générateurs d’aérosols radioactifs étudiés, nous avons conçu une enceinte d’essai transportable permettant de capter les particules et de les échantillonner avec une précision connue, un niveau de bruit de fond très faible et une capacité d’enregistrer les émissions transitoires courtes. Nous présentons les opérations de caractérisation de ce système et les résultats obtenus avec des patients. Ces résultats montrent que l’activité émise en ambiance par les fuites du générateur est supérieure à celle déposée dans les poumons du patient par inhalation, soit respectivement 5,7 % et 3,8 % de l’activité initialement introduite dans le générateur

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

Molecular understanding of the formation of surface zirconium Hydrides upon thermal treatment under hydrogen of [( SiO)Zr(CH(2)tBU)(3)] by using advanced solid-state NMR techniques

The reaction of [(dropSiO)Zr(CH(2)tBu)(3)] with H-2 at 150 degreesC leads to the hydrogenolysis of the zirconium-carbon bonds to form a very reactive hydride intermediate(s), which further reacts with the surrounding siloxane ligands present at the surface of this support to form mainly two different zirconium hydrides: [(dropSiO)(3)Zr-H] (1a, 70-80%) and [(dropSiO)(2)ZrH2] (1b, 20-30%) along with silicon hydrides, [(dropSiO)(3)SiH] and [(dropSiO)(2)SiH2]. Their structural identities were identified by H-1 DQ solid-state NMR spectroscopy as well as reactivity studies. These two species react with CO2 and N2O to give, respectively, the corresponding formate [(dropSiO)(4-x)Zr(O-C(=O)H)(x)] (2) and hydroxide complexes [(dropSiO)(4-x)Zr(OH)(x)] (x = 1 or 2 for 3a and 3b, respectively) as major surface complexes

Enhanced formation of > C1 Products in Electroreduction of CO2 by Adding a CO2 Adsorption Component to a Gas-Diffusion Layer-Type Catalytic Electrode

SSCI-VIDE+ING+FWI:JECInternational audienc

Deterministic placement of doping atoms on hydroxylated surfaces

An improved approach of semi-conductor doping by Molecular Layer Deposition (MLD) is investigated. Here, dopant-containing molecules are directly grafted onto silica-coated silicon wafers and optimized ligands can provide more effective dopant drive-in annealing. The grafting approach is validated on non-porous silica and successfully transferred onto silicon wafers