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Nanoceria as an Efficient and Cost-Effective Metal-Free Catalyst for the Oxidation of Alcohols
No full textInternational audienceThis study investigates the catalytic properties of nanoceria for the liquid-phase oxidation of aromatic and aliphatic alcohols using t-butyl hydroperoxide as an oxidant without the need for base or supported noble metals. The morphology, reducibility, and reversible H2 adsorption characteristics of ceria were comprehensively studied using X-ray diffraction, BET, HAADF-STEM, H2-TPR, H2-TPD, and X-ray photoelectron spectroscopy. Radical formation was interrogated by electron paramagnetic resonance (EPR) using dimethyl pyrrolidine N-oxide (DMPO) and N-tert-butyl-α-phenylnitrone (PBN) as spin traps, complemented by atomistic simulations to elucidate the influence of trap and radical adduct adsorption on the catalysts on radical abundance. The solvent played a critical role in enhancing the catalytic performance and carbon balance. The catalyst retained its structural integrity during the reaction in acetonitrile and could be reused for at least five consecutive runs. EPR analysis revealed that peroxyl radicals (tBu-OO•) were the predominant reactive species with no detectable formation of oxyl (tBu-O•) radicals, ruling out a Fenton-like catalytic mechanism in solution. Incorporating small amounts of Au (0.5–1.0 wt %) as Au(I) single atoms or clusters reduced the catalytic activity due to a decreased surface reducibility and reversible H2 adsorption despite an increased peroxyl radical formation. However, Au doping did not alter the product distribution. Compared to a benchmark 0.3 wt % Au/TS-1 catalyst, nanoceria achieved a 60% cost reduction and an E-factor of 0.08 (vs 0.2–1.3 for 0.3 wt % Au/TS-1) at equivalent acid production rates, highlighting the economic and environmental benefits
Evaluation intégrée des effets toxicologiques, écotoxicologiques et écologiques de l'ensemble des traitements phytopharmaceutiques utilisés sur une saison culturale : exemple de la pomme de terre en Hauts-de-France
No full textLes produits phytopharmaceutiques utilisés en agriculture contiennent des molécules spécifiquement conçues pour être toxiques pour des organismes cibles. Cependant, leur utilisation peut également entraîner des effets non intentionnels, présentant des risques potentiels pour les écosystèmes et les organismes non cibles, y compris les êtres humains. Les travaux de recherche menés ont permis d’approfondir la compréhension des liens entre l’exposition à ces substances et les effets observés dans l’environnement. En particulier, les études ont mis en évidence comment des niveaux d’exposition, même faibles, peuvent engendrer des effets chroniques sur des organismes non cibles et perturber les écosystèmes. Ces résultats soulignent l’importance de quantifier et de caractériser ces expositions pour mieux évaluer leurs impacts potentiels sur la santé humaine et l’environnement. Les présentations seront suivies d’échanges et de discussions, afin de réfléchir ensemble aux conséquences de ces travaux et d’explorer des perspectives pour construire une agriculture qui soit respectueuse de la santé humaine et de l’intégrité des écosystèmes.National audienceCe projet a permis une évaluation rétrospective des effets liés à l'utilisation de phytopharmaceutiques (PPP) lors de la culture de pomme de terre. Sur le terrain, les sols cultivés présentent une contamination multi-résiduelle par de faibles doses de PPP, qui peut être ancienne, consécutive à la culture ou aux traitements de parcelles proches ; concernant les tubercules, peu de résidus ont été retrouvés, et à des concentrations très faibles. Au laboratoire, suite aux expositions par gavage alimentaire de souris, un effet des PPP utilisés pour la culture et le stockage des tubercules récoltés, transitoire, important sur l'expression des gènes et beaucoup plus réduit au niveau du microbiote intestinal a été observé. Pour les expositions réalisées en microcosmes avec les sols cultivés, les modèles d'écotoxicologie (vers de terre, végétaux) ont exprimé des réponses différentes, mais peu d'effets globalement
Energetics of ionic transport on LiwSixP1-xOyNz amorphous electrolyte
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Réussite étudiante, postures enseignantes ou la délicate équation entre enseigner et former
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Investigating the Effect of Morphology on Nanoparticle Catalyst Reactivity: Example of Anthraquinone Hydrogenation
No full textInternational audienceNowadays, nanomaterials are central in modern technology, finding applications in a huge variety of scientific fields, such as catalysis. Besides their chemical nature, their morphology also appears to play a key role in catalytic processes. Although this effect has been extensively observed in literature, no fundamental explanation has been provided yet. In this work, taking anthraquinone hydrogenation on Pd as a model process, we used density functional theory (DFT) computation to address the particle shape effect. Based on previously published experimental results, we compared the catalytic properties of cubic and octahedral nanoparticles, considering different facet orientations and edge defects to simulate geometry and the size influence. We were able to correlate the morphological impact on the surface activity and selectivity with electronic charges of various intensities, induced at the material topmost layer by the cubic shaped-design, especially close to edges. Such an inequal charge distribution, differently affects the stability of the reaction intermediates according to their polarizability. Besides offering for the very first-time theoretical insights to understand the surface geometry effect on reactivity, this work is expected to have practical implications for experimentalists in the rational design of efficient solid catalysts in many areas of the chemical industry
Fluorinated Phosphates, BaMPO<sub>4</sub>F (M = Mn, Fe), with One-Dimensional Channels: Structure and Magnetism
No full textInternational audienceTwo transition metal fluoride phosphates, BaMPO4F (M = Mn, Fe), are prepared through hydrothermal redox reactions and analyzed using XRD, XPS, Mössbauer spectroscopy, and density functional theory (DFT). The modified fluoride-rich hydrothermal routes combining two reducing sources, i.e., hydrazine and hypophosphorous acid, to grow Fe(II)-based fluorinated phosphates are described. Both crystal structures consist of three-dimensional (3D) frameworks formed by connected [M2+O4F]7– and PO43– polyhedra, containing 8-membered rings (8MR) and 6MR cross-stitched 1D channels filled by Ba2+ ions. BaMnPO4F is isostructural to BaZnPO4F with an orthorhombic space group Pna21, while BaFePO4F (S.G. P212121) is isotypic to BaMPO4F (M = Cu and Co) analogues. Magnetic susceptibilities χ(T) and specific heat Cp(T) for BaMnPO4F (I) and BaFePO4F (II) reveal antiferromagnetic ordering below 5.8 K (I) and 11.3 K (II), with all magnetic exchanges resulting from supersuper-exchange interactions. Above TN, χ(T) is analyzed on the basis of the most plausible low-dimensional subunits, decoupled above the long-range AFM ordering. The analysis of the density-of-states (DOS) by DFT+U calculations validates the crystal-field splitting of the local MO4F trigonal bipyramids with significant overlap due to their strong structural distortions, and validates the lower-energy levels of F-2p compared to O-2p levels due to their enhanced ionic character
Cellulose nanocrystals-supported organocatalyst for the synthesis of cyclic carbonates via cycloaddition of carbon dioxide to epoxide
No full textInternational audienceThe synthesis of cyclic carbonates can be realized via cycloaddition of CO2 to epoxides. Organocatalysts are of interest regarding specific applications. The reaction can be co-activated by a hydrogen bond donor such as cellulose. A fully recyclable catalytic system combining an organocatalyst and a polysaccharide hydrogen bond donor has never been reported. In this study, we have supported an organocatalyst onto cellulose nanocrystals (CNC). The grafting of 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD) onto microcrystalline cellulose (MCC) and onto the surface of cellulose nanocrystals (CNC) was confirmed by 13C solid state NMR, FT-IR, XRD and elemental analysis. The prepared heterogeneous TBD-CNC nanocatalyst was successfully assessed on a scope of five epoxides including mono- and di-substituted. The activity was found to be higher than that of the TBD-MCC supported catalyst, and higher than the homogeneous counterpart. That latter result highlights the coactivation role of the polysaccharide. Recyclability studies showed that the catalyst is reusable for at least five cycles. Density functional theory (DFT) studies indicate that the mechanism most probably involves the formation of anionic cellulosic species. Initially, the grafted TBD deprotonates a surface hydroxy to form a cellulose alkoxide, which then performs a nucleophilic attack on CO2 or on the activated epoxide
