Comparaison physico-chimique et des [sic] activités catalytiques dans les réactions d'oxydation entre deux séries de catalyseurs Ag/CeO préparés par imprégnation et dépôt-précipitation

La cérine est connue pour être très performant en tant que support, dans le domaine de l'oxydation catalytique. L'ajout de métaux de transitions améliore en général cette activité. Dans ce travail, l'argent a été ajouté sur la cérine. Deux méthodes de préparation ont été utilisées : l'imprégnation (Imp), connue par la formation de particules de tailles différentes sur la surface du support, et le dépôt-précipitation (DP) qui conduit en général à la formation de nanoparticules dispersées sur la surface et dans la masse du support. Deux séries de catalyseurs x%Ag/CeO (Imp) et x%Ag/CeO (DP) où x est le pourcentage massique de l'argent par rapport à la cérine, ont été préparés dans le but de comparer leurs propriétés physico-chimiques. Ensuite leurs activités catalytiques dans les réactions d'oxydation. Les catalyseurs ont été caractérisés par différentes techniques telles que la BET, la DRX, la RPE, l'ATD-ATG, la SPX, l'UV et la RTP. Dans les deux séries de catalyseurs, la DRX a montré que des particules de Ag ont été obtenues pour les fortes teneurs en argent ; ces particules sont plus grosses dans les imprégnés que dans les (DP). La présence des nanoparticules dans les deux séries de solides a été aussi confirmée par l'UV (résonance plasmonique). Ces nanoparticules sont de formes sphériques dans les (DP) et mi-sphériques, ou déformées, dans les (Imp). Trois états d'oxydation : Ag , Ag et Ag ont été identifiés dans les imprégnés et seulement deux : Ag et Ag dans les DP. La formation des ions Ag semble être due à la présence de AgNO sur la cérine au cours de la calcination du solide, ce qui était le cas pour les imprégnés et non pour les DP. De plus, les deux isotopes Ag et Ag ont été mis en évidence par la technique de la RPE ; ce résultat est considéré comme original et primordial. Par la suite, les deux séries de catalyseurs ont été testés dans les réacctions d'oxydations catalytique du propène, du monoxyde de carbone et du noir de carbone. Le résultat inattendu dans ce travail c'est que, contrairement à la bibliographie, les catalyseurs imprégnés étaient plus actifs que les (DP) pour les trois réactions. La performance catalytique des imprégnés a été reliée à la présence des espèces Ag qui sont absents dans les DP. Autrement exprimé à la présence de trois couples redox Ag / Ag , Ag / Ag et Ag / Ag dans le cas des solides (Imp), pour seulement un couple redox Ag / Ag dans le cas des solides (DP). Une présence adéquate dans les rapports de concentrations de ces trois couples redox dans le catalyseur 10%Ag/CeO (Imp) a rendu ce dernier le plus performant comparé aux autres de la même série.Ceria is a well known support in the world of catalytic oxidation reactions. Adding transition metals tend to enhance the catalytic activity. Silver was used in our work, and was added using two different preparation methods : the impregnation (Imp) and the deposition-precipitation (DP). The first known by the formation of different particles size on the surface of the support, whereas the second is known by the formation of nanoparticles with a good dispersion on the surface and in the bulk of the support. Two catalysts series x%Ag/CeO (Imp) and x%Ag/CeO (DP) (where x is the weight percentage of silver over ceria) were prepared in order to compare their physico-chemical properties and afterward their catalytic performances in three different oxydation reactions. The catalysts were characterized using BET, XRD, EPR, DSG-TG, XPS, UV and TPR techniques. XRD showed on both series the formation of Ag particles for the catalysts with high weight percentages. The sizes of these particles are larger in the (Imp) solids compared to the (DP) ones. Beside of these particles, the formation of Ag nanoparticles was confirmed by the plasmonic resonance in the UV technique. The nanoparticles are spherical in the (DP) solids and half spherical (misshaped) in the (Imp) solids. Three oxidation states were found in the (Imp) catalysts : Ag , Ag et Ag compared to only two in the (DP) : Ag et Ag . The nitrate present in the AgNO (silver precursor) during the calcination might be the reason of the formation of the Ag . That is not the case for the (DP) solids. The two isotopes for Ag ( Ag and Ag ) were identified with the EPR technique. This result is considered as original and very important. Afterward, the catalysts were tested in the total oxidation of the propylene, carbon monoxide and carbon black. The catalytic results were unexpected and oppose the literature results. (Imp) catalysts showed a higher activity than the (DP) in all the reactions. The catalytic performance of the (Imp) was ascribed to the presence of Ag species that are missing in the (DP) catalysts. In other words, this performance is related to the presence of the 3 redox couples Ag / Ag , Ag / Ag et Ag / Ag for the (Imp), compared to only one : Ag / Ag for the (DP). The 10%Ag/CeO (Imp) solid showed an appropriate concentration ratio of the redox couples, that's why it showed the highest catalytic activity among the other solids from the same series.DUNKERQUE-SCD-Bib.electronique (591839901) / SudocSudocFranceF

Catalytic Oxidation of Carbon Black Over Ru/CoxMgyAl2 Catalysts

AbstractDifferent catalysts based on ruthenium impregnated on hydrotalcites (Ru/CoxMgyAl2-HT) were prepared by wet impregnation from aqueous nitrosyl nitrate solutions and activated under air at 600°C for 4h. The reactivity of the catalysts was evaluated in the oxidation of carbon black (CB). The results showed that the best catalyst decreased the temperature at which the rate of carbon black oxidation is the highest by about 150°C. This good reactivity was attributed to the formation of easily reducible ruthenium and cobalt oxide species at the surface of the support. The addition of ruthenium made the reduction of surface and bulk cobalt oxides possible at lower temperatures

Catalytic Oxidation of Propylene, Toluene, Carbon Monoxide, and Carbon Black over Au/CeO 2

Au/CeO2 solids were prepared by two methods: deposition-precipitation (DP) and impregnation (Imp). The prepared solids were calcined under air at 400°C. Both types of catalysts have been tested in the total oxidation of propylene, toluene, carbon monoxide, and carbon black. Au/CeO2-DP solids were the most reactive owing to the high number of gold nanoparticles and Au+ species and the low concentration of Cl- ions present on its surface compared to those observed in Au/CeO2-Imp solids

Design and assembly of covalently functionalised polyoxofluorovanadate molecular hybrids

Mixed-valent polyoxometalate (POM) clusters are one of the most interesting host species showing a wide range of structural features and properties. We report the facile preparation and functionalization of a mixed-valent polyoxofluorovanadates where two electrons are trapped to antipodal sites of the clusters. The first members of this family of clusters with the general formula, [VV12VIV2O16(μ-O)10(μ3-O)10(μ3-F)2(L)2]6-, where L: py = pyridine (1); pyr = pyrazine (2); im = imidazole (3), are unique organic-inorganic hybrids with the addition of a N-donor ligand at either end of the polyoxofluorovanadate. The composition and connectivity of 1 - 3 were characterized by single-crystal X-ray diffractometry and electrospray ionization mass spectrometry. Electron paramagnetic resonance spectroscopy revealed the two well-separated VIV ions in each cluster are fully uncoupled with J = 0 giving a degenerate singlet-triplet ground state. This attenuation of the exchange interaction is probed with density functional theoretical calculations that detail the inclusion of the fluoride ion in the cluster produces a bond pathway biased toward destructive interference between competing ferromagnetic and antiferromagnetic interactions. These robust molecular materials are the ideal combination of desirable electronic properties with an organic handle with which they can be integrated into spintronic circuitry for molecular devices

Directed self-assembly, symmetry breaking, and electronic modulation of metal oxide clusters by pyramidal heteroanions

Mixed valence/metal polyoxometalate (POM) clusters are one of the most interesting host species showing the ability to incorporate a wide range of heteroatoms of various charges and geometries. We report herein, the incorporation of different pyramidal EO32- heteroanions (E = PH, S, Se, Te) which are responsible not only for directing the templated assembly of a family of mixed-metal POMs but also for the symmetry-breaking of the traditional Dawson architecture and modulation of the electronic characteristics of the cluster's shell. The isolated family of POMs consists of four members: (Me2NH2)5Na2[Mo11V7O52(HPO3)]·MeOH·5H2O (1), (NH4)7[Mo11V7O52(SO3)]·12H2O (2), K7[Mo11V7O52(SeO3)]·31H2O (3), (Me2NH2)6Na[Mo11V7O52(TeO3)]·15H2O (4), and were characterized by X-ray structural analysis, electrospray ionization mass spectrometry (ESI-MS), thermogravimetric analysis (TGA), UV-vis, IR, elemental and flame atomic absorption spectroscopy (FAAS) analysis, and inductively coupled plasma optical emission spectroscopy (ICP-OES). Cyclic voltammetry (CV) and electron paramagnetic resonance (EPR) spectroscopic studies in concert with density functional theoretical (DFT) calculations elucidate the effect of the heteroatom on the electronic properties of the cluster

Lésions spinales intracanalaires dans la neurofibromatose de type 2

LILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF