A study of surface and structural changes of magnetite cycling material during chemical looping for hydrogen production from bio-ethanol

Magnetite samples were synthesized and studied as the cycling material of a chemical loop process for hydrogen production from ethanol and water used as reducing and oxidizing species, respectively. Surface and structural changes during the process were characterized by various techniques such as X-ray diffraction, X-ray photoelectron, and Mossbauer spectroscopy in order to evidence the real cycling process and understand the cause of the material deactivation so that it can be suppressed or minimized for an industrial application. We found that the complete recovery of the initial cycling material was possible, but that a slow accumulation of coke took place over time under cycling conditions. Indeed, this deposited coke corresponds to only a part of the coke formed, since water makes partial re-oxidation possible. A third step to burn the coke left over by the air will thus have to be periodically added for a sustainable industrial process, unless a cycling material and/or certain conditions capable of either totally preventing the formation of coke or leading to the formation of coke that is not oxidized by water are found

Comportement chimique du titane dans un alliage liquide aluminium-silicium

Le présent travail s'inscrit dans le cadre d'un programme visant à réaliser des assemblages titane/alliage d'aluminium. A cette fin, une étude générale des interactions chimiques dans le système Al-Si-Ti a été entreprise. En premier lieu, l'aspect thermodynamique de ces interactions a été précisé par la détermination expérimentale des équilibres liquide-solide s'établissant à 1000 K dans le système ternaire Al-Si-Ti. Dans une deuxième étape, les zones de réaction interfaciales formées à différents stades de l'interaction entre le titane et un alliage liquide Al-Si ont été caractérisées par microscopie (optique et électronique) et microsonde électronique. A partir des résultats obtenus, un mécanisme réactionnel est proposé pour décrire la cinétique de croissance de ces zones

Distribution des espèces Ge dans le réseau des zéolithes par incorporation post-synthèse d'ions F-

National @ MATERIAUX+XLI:FBS:GBR:ATUInternational audienceNon

Stabilité thermique de la phase β\betaAl5_5FeSi dans le système ternaire Al-Fe-Si

DTA and isothermal diffusion experiments have been carried out at temperatures up to 727 $^{\circ}$C in the Fe-Al-Si ternary system. in these experiments, we have observed the themal decomposition of the solid ternary compound $\beta$Al$_5$FeSi ($\tau$6) into another ternary compound, $\gamma$Al$_5$Fe$_2$Si$_2$ ($\tau$2), and a liquid. Under the atmospheric pressure, that decomposition of $\beta$Al$_5$FeSi occurs at temperatures ranging hnn $661 \pm 5$ $^{\circ}$C to $667 \pm 5$ $^{\circ}$C. A polythermal projection combining these new results with previously published data is given to describe the crystallisation of ternary Al-Fe-Si liquid alloys upon slow cooling from 727 $^{\circ}$C

A study of surface and structural changes of magnetite cycling material during chemical looping for hydrogen production from bio-ethanol

RX+ECI2D+CTR:FBS:JMIInternational audienc

On the promoting effect of H2S on the catalytic H-2 production over Gd-doped ceria from CH4/H2O mixtures for solid oxide fuel cell applications

ENERGIE:MATERIAUX:SURFACES+GPO:FBS:GBR:NSP:PGEIn order to understand the exceptional tolerance of ceria to high sulfur levels in the fuel for further SOFC applications, the interaction of sulfur with a commercial Ce0.9Gd0.1O2-x (CGO, from Praxair) and its influence on H-2 production from CH4/H2O mixture was studied. The activity tests were performed at 750 C, in the presence of H2S and under gradual internal reforming conditions (large excess of CH4 with respect to water vapor, 10:1). The presence of H2S in the reactant mixture promoted the catalytic activity of CGO. The nature of various species formed by sulfur-ceria interaction is discussed based on CH4-TPR, XRD, XPS, and in situ FTIR results. H2S reacts with ceria fraction in CGO and generates new catalytic sites with improved reactivity toward CH4. The formation and stabilization of oxygen vacancies by S-insertion in ceria lattice are evidenced and directly related to the improved activity. The detrimental effect of Ce2O2S phase, when formed, on the catalytic activity of doped ceria is confirmed. (C) 2014 Elsevier Inc. All rights reserved

Affinement expérimental de l'isotherme Al-Fe-Si à 1000 K

With more than fifteen reported stable binary and ternary compounds, the Al-Fe-Si phase diagram is rather complex. To get a better insight into that diagram, experiments were carried out by isothermal diffusion and thermal analysis. The results of these experiments have been combined with previous data to provide a refined Al-Fe-Si section at 1000 K

Probing Ge Distribution in Zeolite Frameworks by Post-Synthesis Introduction of Fluoride in As-Made Materials

MATERIAUX+URA:FBS:GBR:ATUA new method has been developed to introduce fluoride in the structure of as-made germanium-containing zeolites prepared under pure alkaline media. Incorporation of fluoride species occurs without modification of the framework composition (Si/Ge ratio) and of the crystallinity, as evidenced by Xray diffraction and electron microscopy. After incorporation, F-19 solid-state NMR has been used to probe the location and distribution of Ge atoms in the framework. In the case of ITQ-13 and ITQ-17, which can be prepared from both hydroxide and fluoride routes, incorporated F anions are located in the same structural units as those occupied when zeolites are prepared in the presence of fluoride. In the case of ITQ-22 and ITQ-24, fluoride goes mainly in D4R units, which appear to be in the most energetically favorable positions for these zeolites. All experiments clearly show that zeolites prepared in the absence of fluoride in the synthesis medium are enriched in germanium, compared to the same materials obtained from F-containing gels. Moreover, Ge plays a strong structure-directing role by replacing Si atoms preferentially in D4R, leading to zeolites with mainly [4Si, 4Ge] units in the framework. In the particular case of ITQ-22, a new line observed around -2 ppm in F-19 NMR spectra has been tentatively assigned to [3Si, 5Ge] D4R units, which corroborates the structural data obtained via X-ray diffraction