Catalyseurs à base d'or pour la purification des alcènes légers par hydrogénation sélective

Ces travaux ont porté sur la compréhension de la réaction d'hydrogénation sélective des hydrocarbures par des catalyseurs Au. Trois méthodes de préparation de catalyseurs ont été approfondies et revisitées, et nous avons notamment montré qu'il est possible d'obtenir de petites particules d'or (2-3 nm) supportés sur différents oxydes à partir de méthodes de préparation simples. Nous avons ensuite mis en évidence l excellente sélectivité de l or pour cette réaction. La réactivité de l'or en hydrogénation est très différente de celle en oxydation: la nature du support n a pas d influence sur la réaction, et celle-ci n'est pas sensible à la structure des particules d'or. Enfin si le Pd est sélectif grâce à une compétition d'adsorption, l'or reste sélectif quelle que soit la concentration en butadiène. Ces propriétés uniques pourraient en faire un excellent catalyseur de finition. La désactivation de ces catalyseurs a aussi été abordée et les potentialités des catalyseurs Au-Pd explorées.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Trapping AsPh3 via reaction with NiS/γ-Al2O3 in the presence of H2: Reaction mechanism and kinetics

International audienceRemoval of As from petroleum feedstocks is an important process which can be realized using As trapping mass containing supported nickel sulfide. In order to understand the mechanism of the trapping we studied the reaction of AsPh3 with NiS/γ-Al2O3 in the presence of H2 in a batch reactor in toluene solution at 230 °C. This reaction results in formation of NiAs, benzene and H2S. Also, the intermediate species, thiophenol and diphenylsulfide, were observed. Despite formation of NiAs layer in the course of reaction, the rate of AsPh3 decomposition is not affected by the solid state diffusion up to ∼ 50 % of nickel conversion. The rate determining step in these conditions appears to be the hydrogenolysis of As-C bonds. It was found that the reaction order changes in the course of reaction from zero to one. This trend is described by a kinetic model assuming adsorption of AsPh3 molecules followed by decomposition

The influence of MoS2 slab 2D morphology and edge state on the properties of alumina-supported molybdenum sulfide catalysts.

International audienceTo study the influence of MoS2 particles morphology on their catalytic properties, a series of MoS2/Al2O3 catalysts was prepared, by means of treatment of oxide precursor under variable conditions. The conditions of treatment were selected to generate the MoS2 crystallites exposing preferentially M-edges or M- and S-edges, as predicted by the theory phase diagrams. The MoS2 particles size was estimated by electron microscopy and the degree of sulfidation to MoS2 was determined from X-ray photoelectron spectroscopy. The edge state of MoS2 particles was probed by FT-IR of adsorbed CO and by temperature programmed reduction (TPR). Hydrogenation (HYD) selectivity and hydrodesulfurization (HDS) selectivity were estimated from the catalytic tests using hydroconversion of 2,3-dimethylbut-2-ene and 3-methylthiophene. It seems that the variations of 2D morphology of MoS2 particles influence the HYD/HDS selectivity. However, a drastic drop of activity was observed when the preparation temperature increased from 250 to 700 °C which cannot be accounted by the decrease of the amount of exposed edges due to thermal sintering. At the same time a drastic loss of ability to adsorb CO and harder reducibility of sulfide edges were observed for the samples prepared at high temperatures. The results suggest that well crystallized edges of MoS2 bearing no excess sulfur have low activity whatever their symmetry type

Genèse d'une acidité modérée au sein des catalyseurs destinés au prétraitement des procédés de craquage catalytique (FCC) et d'hydrocraquage (HCK)

L utilisation de procédés de conversion comme le craquage catalytique (FCC) et l hydrocraquage (HCK), permettant de maximiser la production de coupes légères, est indispensable. Les charges à convertir contiennent une quantité importante de soufre et d azote et doivent être prétraitées, c est-à-dire hydrotraitées, afin de diminuer la teneur en soufre et en produits azotés pour éviter l empoisonnement des catalyseurs acides des procédés de FCC et HCK. Les catalyseurs actuellement utilisés possèdent uniquement une fonction hydro-deshydrogénante amenée par les sulfures métalliques. Ce travail propose d introduire une acidité modérée dans des catalyseurs de prétraitement de type NiW supportés sur alumine. L acidité modérée peut promouvoir l isomérisation des composés soufrés réfractaires (comme le 4,6-DMDBT) en facilitant ainsi leur hydrodésulfuration. Pour l HDN, les sites acides peuvent faciliter la coupure des liaisons C N, sur des molécules totalement ou partiellement hydrogénées. Cette acidité est introduite par le biais du niobium, du silicium et du bore.Pour contrôler la dispersion des sites acides au voisinage des sites hydro-déshydrogénants, les éléments Nb/Si/B et W sont initialement introduits au sein de la même entité moléculaire de type hétéropolyanion. Plusieurs HPA contenant le niobium, le silicium, le bore et le tungstène ont été synthétisés et caractérisés. Les catalyseurs sont préparés par imprégnation avec des solutions des précurseurs et caractérisés à l état oxyde et sulfure. Les catalyseurs ont été testés en hydrogénation du toluène en présence de soufre (sans et avec aniline) et en isomérisation du cyclohexane et comparés avec des catalyseurs de référence préparés avec des précurseurs conventionnels. Les catalyseurs, promus par le nickel, préparés à partir d acides silicotungstique ou borotungstique se sont révélés performants en isomérisation tout en maintenant une activité hydrogénante élevée ; l utilisation d HPA a également permis une dispersion homogène des sites acides et hydrogénants ce qui en fait de bons candidats pour l HDS et HDN de molécules réfractaires, et donc des potentiels catalyseurs de prétraitement.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

IR Spectroscopic Evidence for MoS 2 Morphology Change with Sulfidation Temperature on MoS 2 /Al 2 O 3 Catalyst

Accessed by 02/2015International audienceLow temperature CO adsorption followed by IR spectroscopy (IR/CO) characterization was used to depict the MoS2 morphology change with sulfidation temperature on MoS2/Al2O3 catalyst. It is found that the morphology of MoS2 slabs on MoS2/Al2O3 catalyst under typical sulfidation temperature range (573 to 723 K) is a truncated triangle exposing both the M-edge and S-edge. Moreover, the IR/CO data indicate that the truncation degree (ratio of S-edge/M-edge) of MoS2 slabs gradually increases with increasing sulfidation temperature. This finding is in line with density functional theory calculation on model catalysts, providing IR evidence of MoS2 morphology change with sulfidation temperature on an Al2O3-supported catalyst. As a further step, it is also found that the MoS2 morphology is strongly influenced by MoS2–Al2O3 interactions under the same sulfidation temperature

Longitudinal profile of estrogen-related thrombotic biomarkers after cessation of combined hormonal contraceptives

The persistence of risk of venous thromboembolism (VTE) due to combined hormonal contraceptives (CHC), after their cessation, is unknown, but is important to guide clinical practice. Our objective was to conduct a prospective cohort study to define the time until normalization of the estrogen-related thrombotic biomarkers after CHC cessation. We enrolled women aged 18-50 years who had decided to stop their CHC, excluding those with a personal history of VTE, current anticoagulation, a recent medical event or pregnancy. The study started prior to cessation of CHC, with 6 visits afterwards (at 1-2-4-6-12 weeks post-cessation). Primary outcomes were normalized sensitivity ratios to activated protein C (nAPCsr) and to thrombomodulin (nTMsr), with sex hormone-binding globulin (SHBG) as a secondary endpoint. We also included women without CHC as controls. Among 66 users of CHC, from baseline until 12w, average levels of nAPCsr, nTMsr and SHBG decreased from 4.11 (SD2.06), 2.53 (SD1.03) and 167 nmol/L (SD103) to 1.27 (SD0.82), 1.11 (0.58) and 55.4nmol/L (SD26.7), respectively. On a relative scale, 85.8%, 81.3% and 76.2% of the decrease from baseline until 12 weeks was achieved at 2 weeks, and 86.7%, 85.5% and 87.8% at 4 weeks after CHC cessation, respectively. Levels were not meaningfully modified throughout the study period among 28 control women. In conclusion, CHC cessation is followed by a rapid decrease in estrogen-related thrombotic biomarkers. Two to four weeks of cessation prior to planned major surgery, or withdrawal of anticoagulants in VTE patients, appears sufficient for the majority of women

Tortuosity of mesoporous alumina catalyst supports: Influence of the pore network organization

International audienceInverse liquid chromatography experiments were performed on five mesoporous alumina catalyst supports with similar porosity and different pore size distributions. By varying the size of the molecular tracer, it was shown that the diffusion regime in our conditions is molecular diffusion. Hindered diffusion was not observed even for squalane, a C 30 molecule. Using the slope of the Van Deemter equation, the tortuosity of each alumina support was determined. The results are in disagreement with literature correlations: although all alumina supports had similar total porosities, the measured tortuosity values are really different and much higher than those predicted by these theoretical models. This discrepancy has been resolved by assuming a two–level pore network organization, whose characteristics can be entirely estimated from a classical nitrogen adsorption isotherm. This simple methodology allows to evaluate the mass transfer in mesoporous alumina supports knowing their textural properties, which is an important issue for the design and optimization of numerous catalytic processes

Niobium–Containing Lindqvist Isopolyanions [NbxW6–xO19](2+x)– Used as Precursors for Hydrodesulfurization Catalysts with Isomerization Properties

International audienceLindqvist isopolyanions [NbxW6–xO19](2+x)– (x = 0–4 and 6) were prepared and their spectroscopic and thermal properties were determined by Raman and IR spectroscopy as well as TGA/DSC. The structure of the [NbW5O19]3– anion obtained as single crystal was determined. Ni-promoted alumina-supported hydrodesulfurization (HDS) catalysts were prepared from the best soluble NbW polyoxometalates. In the calcined catalysts, better dispersion of the metallic species is observed when using NbW isopolyanions instead of the conventional ammonium metatungstate. The presence of niobium was expected to introduce acidity leading to isomerization property in classical NiW HDS catalysts. In HDS reaction conditions (under hydrogen pressure and sulfided environment) the cyclohexane isomerization into methylcyclopentane activity of niobium-based catalysts was found up to 5 times superior to that of conventional NiW catalyst, showing the beneficial effect of niobium for this reaction

PTK2B/Pyk2 overexpression improves a mouse model of Alzheimer's disease

Pyk2 is a Ca2+-activated non-receptor tyrosine kinase enriched in forebrain neurons and involved in synaptic regulation. Human genetic studies associated PTK2B, the gene coding Pyk2, with risk for Alzheimer's disease (AD). We previously showed that Pyk2 is important for hippocampal function, plasticity, and spine structure. However, its potential role in AD is unknown. To address this question we used human brain samples and 5XFAD mice, an amyloid mouse model of AD expressing mutated human amyloid precursor protein and presenilin1. In the hippocampus of 5XFAD mice and in human AD patients' cortex and hippocampus, Pyk2 total levels were normal. However, Pyk2 Tyr-402 phosphorylation levels, reflecting its autophosphorylation-dependent activity, were reduced in 5XFAD mice at 8 months of age but not 3 months. We crossed these mice with Pyk2−/− mice to generate 5XFAD animals devoid of Pyk2. At 8 months the phenotype of 5XFAD x Pyk2−/− double mutant mice was not different from that of 5XFAD. In contrast, overexpression of Pyk2 in the hippocampus of 5XFAD mice, using adeno-associated virus, rescued autophosphorylated Pyk2 levels and improved synaptic markers and performance in several behavioral tasks. Both Pyk2−/− and 5XFAD mice showed an increase of potentially neurotoxic Src cleavage product, which was rescued by Pyk2 overexpression. Manipulating Pyk2 levels had only minor effects on Aβ plaques, which were slightly decreased in hippocampus CA3 region of double mutant mice and increased following overexpression. Our results show that Pyk2 is not essential for the pathogenic effects of human amyloidogenic mutations in the 5XFAD mouse model. However, the slight decrease in plaque number observed in these mice in the absence of Pyk2 and their increase following Pyk2 overexpression suggest a contribution of this kinase in plaque formation. Importantly, a decreased function of Pyk2 was observed in 5XFAD mice, indicated by its decreased autophosphorylation and associated Src alterations. Overcoming this deficit by Pyk2 overexpression improved the behavioral and molecular phenotype of 5XFAD mice. Thus, our results in a mouse model of AD suggest that Pyk2 impairment may play a role in the symptoms of the disease