La longue séquence pliocène de Marchésieux - Résultats analytiques et premiers résultats

National audienceLe sondage intégralement carotté de Marchésieux a permis d'atteindre l'objectif fixé dans le projet AR42 du BRGM : l'analyse paléoclimatique du premier épisode glaciaire de l'hémisphère nord (Prétiglien, -2,4 Ma) et probablement le premier rafraîchissement de -3,1 Ma. Les 159,3 m de sédiments datés du Reuvérien et du Prétiglien ont déjà livré une quantité importante d'informations aussi bien climatiques que paléoenvironnementales. De par sa position géographique privilégiée et de par son environnement côtier, la "Longue sequence" de Marchésieux a précisé les modalités de la séquence de dégradation climatique en milieu continental et marin à nos latitudes moyennes. La méthodologie fortement pluridisciplinaire, le plus souvent il très haute résolution, permet d'affiner notablement les modalités de la réponse de chaque environnement au changement climatique, et apparaît, en ce sens, beaucoup plus riche que les études monodisciplinaires classiques. Ainsi, les réponses zoologiques, phytosociologiques, sedimentologiques et géochimiques au stimulus climatique externe peuvent être comparées et calibrées

Characterization of lamellar or nanostructured materials based on oxides of transition metals for liquid phase catalysis

International audienc

Correlations between Acidity, Surface Structure, and Catalytic Activity of Niobium Oxide Supported on Zirconia

International audienceThe development of the acidity and the relationship between acidity, catalytic activity, and the surface structure for niobium oxide supported on zirconia were investigated for a series of solids. The catalysts were active for 2-propanol dehydration only above a threshold in Nb loading. The acidity was studied by infrared spectroscopy of adsorbed 2,6-dimethylpyridine as a probe molecule, and the onset of activity was correlated with that of the formation of relatively strong Brnsted acid sites. The variation in the abundance of these sites also correlated with the catalytic activity. Raman, IR, and UV spectroscopy results indicated that the active sites were related to polymeric Nb surface species. These results were compared to those previously reported for the WOx/ZrO2 catalysts

Characterization of lamellar or nanostructured materials based on oxides of transition metals for liquid phase catalysis

International audienc

Quantitative IR characterization of the acidity of various oxide catalysts

International audienceThe integrated molar absorption coefficients of the infrared bands characteristic of adsorbed lutidine (2,6-dimethylpyridine) were determined for the purpose of quantifying the acid sites of solid catalysts. The integrated molar absorption coefficients were measured for lutidine adsorbed through H-bonding, coordination to Lewis sites and protonation on Brønsted acid sites. The solids were chosen to present all possible bondings with lutidine and to cover a wide range of common types of catalysts or supports: silica, phosphated silica, HY zeolite, alumina, zirconia, WOx supported on zirconia and NbOx supported on zirconia

Chlorinated alumina as an alkylation catalyst: influence of superficial HCl

International audienceChlorinated alumina catalysts were obtained by reacting gamma-alumina with gaseous CCl4 or hydrogen chloride under various conditions. They had chlorine contents between 4 and 6% by weight, and differed in surface acidity. They were tested as catalysts for the alkylation of isobutane with 2-butene using a fixed bed plug flow reactor. Alumina reacted with CCl4 was found inefficient for this reaction. However, the solid chlorinated with HCl above 800 K was able to catalyze alkylation at a temperature as low as 273 K. Moreover, the CCl4-reacted solid could be activated upon further treatment with HCl at moderate temperatures (370 to 550 K). However, the catalytic activity decays after a few hours on stream. The composition of the alkylate varied somewhat with time on stream: large amounts of cracked products appeared during the initial period, after which the selectivity to trimethylpentanes (TMP) was comparable to that of other solid catalysts. The presence of hydrogen chloride bound to the catalyst surface was established by measuring the temperature-programmed desorption (TPD) of HCl from the various Al2O3–Cl. For the active catalysts, desorption started at temperatures (350–400 K) well under those for the CCl4-treated sample, but all solids continuously released HCl above 650 K. Thus, HCl interacts with particular Lewis acid sites of Al2O3–Cl, and creates the strong Brønsted sites required for catalytic alkylation

Acidity, reactant intercalation and reactivity of layered transition metal oxides in the liquid phase

International audienc

Characterization of layered transition metal oxides for liquid phase catalysis

International audienc

Chlorinated alumina as an alkylation catalyst: influence of acidity moderators

International audienceChlorinated alumina catalysts obtained by reacting a gamma-alumina with hydrogen chloride show high initial activity in isobutane-butene alkylation. After a few hours on stream however, the conversion decays due to self poisoning. This work attempts at improving the catalyst lifetime by modifying the Al2O3-Cl catalyst. Best results were obtained by adding small amounts of alkaline cations to the alumina before chlorination. For a particular cation, lithium or sodium, the improvement in catalyst lifetime depends on the chlorination procedure (pre-treatment with CCl4, final temperature). Addition of cations also enhances the selectivity for octanes, mainly by decreasing the amount of cracked products. Degradation of 2,2,4-trimethylpentane was found to occur over the Al2O3-Cl catalysts at 273 K. The influence of cation addition on this process was examined. Thus, the occurrence of dimethylhexanes and cracked or heavier alkanes among alkylation products may be explained by the degradation of 2,2,4-TMP

Characterization of layered transition metal oxides for liquid phase catalysis

International audienc