Avoiding Loss of Catalytic Activity of Pd Nanoparticles Partially Embedded in Nanoditches in SiC Nanowires

Nanoditches from selective etching of periodically twinned SiC nanowires were employed to hinder the migration and coalescence of Pd nanoparticles supported on the nanowires, and thus to improve their catalytic stability for total combustion of methane. The results show that the etched Pd/SiC catalyst can keep the methane conversion of almost 100% while the unetched one has an obvious decline in the catalytic activity from 100 to 82% after ten repeated reaction cycles. The excellent catalytic stability originates from the limitation of the nanoditches to the migration and growth of Pd nanoparticles

A Roadmap for Using the UN Decade of Ocean Science for Sustainable Development in Support of Science, Policy, and Action

The health of the ocean, central to human well-being, has now reached a critical point. Most fish stocks are overexploited, climate change and increased dissolved carbon dioxide are changing ocean chemistry and disrupting species throughout food webs, and the fundamental capacity of the ocean to regulate the climate has been altered. However, key technical, organizational, and conceptual scientific barriers have prevented the identification of policy levers for sustainability and transformative action. Here, we recommend key strategies to address these challenges, including (1) stronger integration of sciences and (2) ocean-observing systems, (3) improved science-policy interfaces, (4) new partnerships supported by (5) a new ocean-climate finance system, and (6) improved ocean literacy and education to modify social norms and behaviors. Adopting these strategies could help establish ocean science as a key foundation of broader sustainability transformations

Moving-Bed Process for Residue Hydrotreating

A lot of chemical, petrochemical or refining processes require contact between three phases : a liquid feed, a gaseous reactant and a solid catalyst. Frequently, the catalyst activity is reduced by poisoning of active sites or coke deposits. This is especially the case with the processes used in heavy residual oils hydrotreating. As the catalyst life is reduced, the substitution or regeneration of the inactive catalyst is frequently necessary. Various solutions, such, as fixed beds used with swing reactors, fluidized beds, or moving beds with down flow of the catalyst and co-current or counter-current of the feed, can be proposed to perform this task with a minimum of time and production losses. A theoretical comparison between the performances of the various technologies has been made by means of a detailed simulation of the behaviour of each of these catalytic beds over a long period. Of course, in the models, some assumptions are necessary, like the ideal fluid and solids flows. Nevertheless, the problem remains complex because hydrodynamic, kinetic, catalyst deactivation, or thermal effects occur simultaneously, within the particules and/or in the bed as a whole. Various pilot plant data are of course used in order to build the kinetic part of the models. This comparison shows a marked advantage for the moving bed with counter-current flow between feed and catalyst owing to the systematic optimum use of the catalyst potential. Consequently, a series of experiments was made on various sized cold mockups designed to simulate counter-current movind beds. These experiments were necessary to demonstrate the feasability of the process, to specify the relations among gas and liquid superficial velocities, particles and fluids properties, and hydrodynamic regimes, and to develop the scale-up rules. The main goal is to secure a uniform distribution of the two fluids through out the whole bed of catalyst, and at the same time a regular progression of the solid particles during the sequential withdrawal. It is the reason why the movement of the solid and, moreover, the residence time distribution of the catalyst particles have been especially followed. To this end, a new technique has been developed to measure the concentration of magnetically marked particles. Furthermore, a specific effort has been devoted to technological problems such as selection and developement of special valves able to insure efficient tightness between the various sections at elevated temperatures and pressures in the presence of solid particles. Another study has been devoted to the operation of addition and withdrawal of the catalyst to and from the reactor running at high pressure and temperature. The solid flows and the catalyst transfer conditions have been carefully studied and tested. Finally a demonstration unit has been built at a semi-industrial scale in a mini-refinery. It was a convincing way to check all the conclusions drawed from the developement step with models, smaller scale pilots and mock-ups. As the fluids and the catalyst were real industrial products, the feasibility of the whole process has been demonstrated. Therefore, a new industrial process using the countercurrent moving bed is now available and permits a very efficient use of the catalyst particles

Baignade urbaine dans la Seine et la Marne : un indicateur de qualité des cours d’eau ?

International audienc

Valence of manganese, in a new oxybromide compound, determined by means of electron energy loss spectroscopy

Electron Energy Loss Spectroscopy, at Mn M2,3 and L2,3 edges is used in order to investigate the ionization state of manganese in a new oxybromide compound. The experimental procedure and the various approaches used to determine Mn oxidation state (edge energy shifts and L3/L2 ratios) are tested on a wellknown manganese oxychloride containing Mn2+ and Mn3+ cations. The comparison of the respective confidence limits of each approach shows that the best precision is obtained with the method based on the energy shifts of the Mn L2,3 edges. That experimental approach applied to the manganese oxybromide allows us to confirm that Mn 4+ is present in this new compound and a reconstruction of the L2,3 white lines, using normalized standard spectra, seems to show the presence of three Mn oxidation states in the material

Use of DFT to achieve a rational understanding of acid?basic properties of ?-alumina surfaces

International audienc

Un siècle de contamination fécale dans la Seine et la Marne au sein de l’agglomération parisienne, et maintenant ?

International audienc

Un siècle de contamination fécale dans la Seine et la Marne au sein de l’agglomération parisienne, et maintenant ?

International audienc