Organic-inorganic supramolecular solid catalyst boosts organic reactions in water

[EN] Coordination polymers and metal-organic frameworks are appealing as synthetic hosts for mediating chemical reactions. Here we report the preparation of a mesoscopic metal-organic structure based on single-layer assembly of aluminium chains and organic alkylaryl spacers. The material markedly accelerates condensation reactions in water in the absence of acid or base catalyst, as well as organocatalytic Michael-type reactions that also show superior enantioselectivity when comparing with the host-free transformation. The mesoscopic phase of the solid allows for easy diffusion of products and the catalytic solid is recycled and reused. Saturation transfer difference and two-dimensional H-1 nuclear Overhauser effect NOESY NMR spectroscopy show that non-covalent interactions are operative in these host-guest systems that account for substrate activation. The mesoscopic character of the host, its hydrophobicity and chemical stability in water, launch this material as a highly attractive supramolecular catalyst to facilitate (asymmetric) transformations under more environmentally friendly conditions.This work was funded by ERC-AdG-2014-671093-SynCatMatch and the Generalitat Valenciana (Prometeo). M.B. acknowledges the funding: CTQ2014-52633-P. The Severo Ochoa program (SEV-2012-0267) is thankfully acknowledged.García García, P.; Moreno Rodríguez, JM.; Díaz Morales, UM.; Bruix, M.; Corma Canós, A. (2016). Organic-inorganic supramolecular solid catalyst boosts organic reactions in water. Nature Communications. 7. https://doi.org/10.1038/ncomms10835S7Li, B. et al. A porous metal-organic framework with dynamic pyrimidine groups exhibiting record high methane storage working capacity. J. Am. Chem. Soc. 136, 6207–6210 (2014).Getman, R. B., Bae, Y.-S., Wilmer, C. E. & Snurr, R. Q. 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Ternary transition metals sulfides in hydrotreating catalysis.

International audienc

Ternary transition metals sulfides in hydrotreating catalysis.

International audienc

Ternary transition metals sulfides in hydrotreating catalysis

International audiencePure microcrystalline barium molybdate BaMoO4 and barium tungstate BaWO4 materials were prepared by molten flux reaction using alkali metal nitrates as reaction media. The obtained crystals have rhombic shape and expose mostly (111) crystallographic planes. Their mean size depends on the flux temperature and the nature of the alkali metal cation. Monomeric molybdate and tungstate used as precursors yield target products already at 673 K whereas if polymerized ammonium oxosalts were used, then higher temperatures were necessary to obtain barium salts. The optimal temperature for the preparation of pure crystals with well defined shape was found to be near 773 K. UV–visible spectra have been measured to precise energy gaps in these important d0 transition metal compounds. The values of Eg for these two mixed oxides are 4.3 eV for BaMoO4 and 3.8 eV for BaWO4. Such values contradict to what can be expected from the known data on their structure and the relative electronegativity of W and Mo ions. The possible xplanations of this observation are commented

Nouveaux oxydes nanostructurés pour la désulfuration (cinétique et mécanismes d'interaction avec le sulfure d'hydrogène et le thiophène)

Ce travail de thèse s inscrit dans le contexte de la désulfuration par absorption des gaz utilisables dans des technologies émergentes comme les piles à combustible ou le procédé Fischer-Tropsch. Cette purification peut être réalisée à des températures modérées (200-300C) sans régénération d'échantillon. L absence de traitements à haute température permet d'envisager l'utilisation des solides nanostructurés qui devraient montrer naturellement une réactivité élevée. En fonction du schéma précis du procédé, on pourra être amené à éliminer des molécules de nature différente : H2S ou des molécules réfractaires comme mercaptans ou thiophènes. Pour répondre à ces exigences, la thèse s'est déroulée en deux parties. Dans la première partie des échantillons à base de nanoparticules de ZnO pur et dopé (M0,03Zn0,97O, M=Fe, Co, Ni, Cu) ont été préparés, caractérisés et leur réactivité vis-à-vis d H2S a été étudiée. Il a été trouvé que le cuivre est le dopant qui permet d améliorer le plus les performances de l échantillon. L'étude du mécanisme de sulfuration par MET, DRX in situ et XPS a permis de conclure que la diffusion des ions O2- à travers la couche de ZnS est l'étape limitante de la sulfuration. Son accélération en présence de cuivre serait due à la formation d'une solution solide Cu2S-ZnS riche en lacunes anioniques. La deuxième partie du travail a été consacrée à l'élimination du thiophène. Un nouveau solide nanocomposite 2,8NiO-H1,8Ni0,6(OH)MoO4 a été mis au point. Sa structure ouverte sous forme de feuillets et sa capacité à se réduire facilement en présence d H2 créent des conditions propices pour l'interaction avec le thiophène et permettent ainsi d'augmenter considérablement sa vitesse de sulfuration en comparaison avec l'échantillon classique à base de Ni/ZnO. Sa haute réactivité avec le thiophène en fait un excellent candidat pour éliminer les traces d autres espèces sulfurées (COS, CS2, mercaptans).This work focuses on the desulfurization by absorption of gases which can be used inemerging technologies such as fuel cells or Fischer-Tropsch process. This purification canbe achieved at low temperatures (200-300C) without regeneration of the sorbent. Theabsence of high temperature treatment allow to use nanostructured solids wich can normallymust exibit higher reactivity. Depending on the process chosen, we will have to eliminatemolecules of different nature : H2S or molecules like mercaptans or thiophene. To answerthese requirements, the thesis work consisted of two parts. In the first part, nanoparticles ofpure and doped ZnO (M0,03Zn0,97O, M=Fe,Co,Ni,Cu) were synthesized and characterized,and their reactivity towards H2S was investigated. It was found that copper is the dopandwhich allow to improve considerably the performances of the sorbent. The study ofsulfidation mechanism by TEM, in situ XRD and XPS allow to conclude that diffusion ofO2- ions trough the ZnS layer is the rate limiting step of sulfidation. The acceleration in thepresence of copper may be due to formation of a solid solution Cu2S-ZnS rich in anionicvacancies. The aim of the second part of this work was to eliminate thiophene. A newnanocomposite solid 2,8NiO-H1,8Ni0,6(OH)MoO4 was prepared. Its layered open structureand its ability to be easily reduced create favorable conditions for interactions withthiophene, and in this way, allow to increase considerably its sulfidation rate (in comparisonwith the sulfidation rate of the classical sample Ni/ZnO). Its high reactivity with thiophenemakes it an excellent candidate for the elimination of other sulfure containing molecules(COS, CS2, mercaptans).DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Sulfidation Mechanism of Pure and Cu-Doped ZnO Nanoparticles at Moderate Temperature: TEM and In Situ XRD Studies

International audienceSulfidation mechanism of pure and Cu-doped ZnO nanoparticles (Cu0.03Zn0.97O and Cu0.06Zn0.94O) at 250 and 350 degrees C was studied by transmission electron microscopy (TEM) and in situ synchrotron XRD. For nondoped ZnO, we observed by TEM that partial reaction with H2S is accompanied by the formation of voids at the ZnO/ZnS interface. This phenomenon (known as the Kirkendall effect) confirms that sulfidation of nanosized ZnO by gaseous H2S proceeds via the outward growth of ZnS: Zn2+ and O2- are transferred to the external (ZnS/gas) surface, where zinc is combined with sulfur and oxygen reacts with protons yielding H2O. During sulfidation of Cu-doped ZnO, the cavities do not form, showing that the sulfidation proceeds by another mechanism, the inward growth, which implies that S' anions diffuse from the external surface to the internal ZnO/ZnS interface, where they exchange with O2- anions. The change of the transformation Mechanism is attributed to a significant acceleration of sulfur transport (lattice or grain boundary) through the Cu-containing ZnS layer due to the presence of sulfur vacancies formed after the charge compensation of Cu1+ replacing Zn2+. The conclusion about the enhanced sulfur diffusion in Cu-containing ZnS is further supported by the time resolved in situ XRD measurements. It is found that in the case of nondoped ZnO the size of formed ZnS crystallites remains constant during reaction. In contrast, a pronounced crystalline growth takes place in Cu-doped samples during sulfidation under rather mild conditions (250 degrees C for Cu0.06Zn0.94O) pointing out a high mobility of sulfur anions in Cu containing ZnS particles