Publications: Articles

Resume: A novel Mn-derived catalyst was prepared starting from biomass of Mn-hyperaccumulating plants growing on metal-rich soils. Recovery of this biomass as value-added ?ecocatalysts? provides incentives for the development of phytoextraction programs on soils degraded by mining activities. Characterization of the resulting plant-based ?Eco-Mn?? catalyst by inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF) and X-ray photoelectron spectroscopy (XPS) demonstrated the presence of unusual polymetallic complexes of Mn(II) in the catalyst, along with Fe(III). Incorporation of these species into montmorillonite K10 as solid support provided a supported Eco-Mn? catalyst, whose properties were investigated for alkene epoxidation with H2O2 (30 wt%)/NaHCO3 (0.2 M) as a green terminal oxidizing reagent. The supported Eco-Mn? catalyst demonstrated a high efficiency for styrene epoxidation, with only 0.31 mol% of Mn, a much lower content of Mn than in previously described Mn-derived heterogeneous catalysts. Whereas Fe was also present in the supported Eco-Mn? catalyst, comparison experiments showed that Fe had only a limited role in the catalysis. The water content in the reaction medium had a beneficial effect, increasing the reaction efficiency. The supported Eco-Mn? catalyst was recycled four times without any loss of activity. Comparison of its properties to those of heterogeneous catalysts made by incorporation of commercial MnCl2.4H2O and FeCl3.6H2O highlighted the superior catalytic activity of polymetallic species present in the biosourced catalyst. The substrate scope of the method was extended to various alkenes, including bulky natural products, which were epoxidized with high yields (up to 99%), sometimes much higher than those obtained with already described Mn-derived heterogeneous catalysts. Finally, by simple adjustments of reaction conditions, the method allowed controlled access to aldehydes by oxidative cleavage of various styrene-derived substrates (up to 93% yield). The method thus constitutes a valuable alternative not only to classical epoxidation reagents, but also to oxidative cleavage of styrene-derived molecules, which usually involves toxic and hazardous reagents.

Equipe: Département CP2S : Chimie et électrochimie des matériaux

Equipe: Département P2M : Surfaces et Spectroscopies

Equipe: Département CP2S : Métallurgie et Surfaces

Equipe: Département SI2M : Microstructures et Contraintes

Resume: We present a detailed study of the evolution of the electrical, galvanomagnetic, and thermodynamic properties of polycrystalline AgxMo9Se11 compounds for 3.4 ? x ? 3.8 at low temperatures (2?350 K). In agreement with density functional theory calculations, the collected data show an overall gradual variation in the transport properties from metallic to semiconducting behavior on going from x = 3.4 to 3.8. The results evidence subtle variations in the electronic properties with the Ag content, typified by both positive and negative phonon-drag effects together with thermopower and Hall coefficient of opposite signs. Analysis of the data suggests that these features may be due to peculiarities of the dispersion of the valence bands in the vicinity of the chemical potential. A drastic influence of the Ag content on the thermal transport was evidenced by a pronounced change in the temperature dependence of the specific heat below 10 K. Nonlinearities in the Cp(T3) data are correlated to the concentration of Ag atoms, with an increase in x resulting in a more pronounced departure from a Debye law. The observed behavior mirrors that of ionic conductors, suggesting that AgxMo9Se11 for x ? 3.6 might belong to this class of compounds.

Equipe: Département CP2S : Chimie et électrochimie des matériaux