Cu–Ga2_{2}O3_{3} nanoparticles supported on ordered mesoporous silica for the catalytic hydrogenation of cinnamaldehyde

Herein, we show that gallium oxide can function as an efficient promoter for the Cu-catalysed hydrogenation of cinnamaldehyde. SBA-15-supported Cu–Ga$_{2}$O$_{3}$ nanoparticles with a constant Cu loading of 5 wt% and two Cu/Ga weight ratios of 5 and 2, respectively, were synthesised by incipient wetness impregnation followed by mild drying. Physico-chemical characterisation revealed that the metal dispersion, and thus the active surface area of copper, can be enhanced nine-fold upon the addition of gallium promoter, boosting the catalytic activity as compared with the unpromoted Cu/SBA-15 catalyst. Likewise, the presence of Ga$_{2}$O$_{3}$ improved the selectivity to cinnamyl alcohol

Cu–Ga2_{2}O3_{3} nanoparticles supported on ordered mesoporous silica for the catalytic hydrogenation of cinnamaldehyde

Herein, we show that gallium oxide can function as an efficient promoter for the Cu-catalysed hydrogenation of cinnamaldehyde. SBA-15-supported Cu–Ga$_{2}$O$_{3}$ nanoparticles with a constant Cu loading of 5 wt% and two Cu/Ga weight ratios of 5 and 2, respectively, were synthesised by incipient wetness impregnation followed by mild drying. Physico-chemical characterisation revealed that the metal dispersion, and thus the active surface area of copper, can be enhanced nine-fold upon the addition of gallium promoter, boosting the catalytic activity as compared with the unpromoted Cu/SBA-15 catalyst. Likewise, the presence of Ga$_{2}$O$_{3}$ improved the selectivity to cinnamyl alcohol

Mixed-phase TiO2 photocatalysts: Crystalline phase isolation and reconstruction, characterization and photocatalytic activity in the oxidation of 4-chlorophenol from aqueous effluents

International audienceAnatase and rutile isolated from Degussa P25 and two other TiO2 commercial samples were used as starting materials for the preparation of different anatasetrutile physical mixtures for the photocatalytic oxidation of 4-chlorophenol from aqueous effluents. Degussa P25 was also used as reference active material. The samples were characterized by X-ray diffraction, nitrogen physisorption, Raman spectroscopy, high-resolution transmission electron microscopy and diffuse reflectance UV vis spectroscopy. A special attention was given to the determination of the band gap energy, by using two methods: Tauc plots and derivative spectroscopy. The second method seems more accurate, eliminating a certain degree of subjectivity, inherent to the Tauc-plot method. The photocatalytic tests showed that Degussa P25 was the most active photocatalyst, followed closely by anatase separated from Degussa P25 and by commercial anatase. The addition of rutile to the anatase powder produced a decrease in the photocatalytic activity. The photocatalytic tests showed that the original Degussa P25 was more active than the anatase phase from its composition, which in turn performed better than the reconstructed P25 in the photocatalytic test given an evidence that the supposed synergistic effect does not operate in this particular case

Selective dissolution of TiO2 crystalline phases: Physicochemical characterization and photocatalytic activity

International audienceIn this study, different commercially available TiO2 powders (Degussa P25, pure anatase, and rutile) were submitted to selective dissolution treatments, with H2O2/NH4OH and 10% HF, known to remove rutile and anatase from physical mixtures. The aim was to check whether a particular separation method designed to remove a specific crystalline phase influences the properties of the other phase from the mixture or not. More precisely, we have studied how the HF dissolution method designed to selectively remove the anatase affected the physicochemical and photocatalytic properties of rutile. In a similar way, the changes in the anatase properties were studied, after the H2O2/NH4OH treatment, initially used to remove rutile from the mixture. All the samples were characterized by X-ray diffraction, nitrogen adsorption–desorption, transmission electron microscopy, diffuse reflectance (DR) ultraviolet–visible, and Raman spectroscopy. The photocatalytic activity of these powders was tested in the oxidation of p-chlorophenol from water. The selective treatment methods not only dissolved the target phase but also changed some physicochemical and the photocatalytic performances of the other TiO2 crystalline phase in a considerable manner. These aspects should be taken into account in the studies regarding the synergistic effects of anatase and rutile, especially in reconstructed TiO2 photocatalysts.Différents oxydes de titane commerciaux (Degussa P25, anatase, rutile) ont été soumis à différents traitements de dissolution sélective, avec H2O2/NH4OH et dans HF 10%, afin de pouvoir séparer les phases rutile et anatase lors de la présence des deux phases cristallines dans un même échantillon. L'objectif est de démontrer si une méthode de séparation particulière, adaptée à la dissolution d'une phase cristalline spécifique, affecte ou non les propriétés de la seconde phase présente dans l'échantillon. L'étude présente ainsi l'effet de la dissolution de la phase anatase par la méthode à l'acide fluorhydrique sur les propriétés physico-chimiques et photocatalytiques de la phase rutile résiduelle. De même, les modifications des propriétés de la phase anatase, après traitement H2O2/NH4OH afin de dissoudre sélectivement la phase rutile, ont été évaluées. Les échantillons ont été caractérisés par différentes techniques: Diffraction de rayons X, physisorption d'azote, microscopie électronique en transmission, spectroscopie UV–vis et spectroscopie Raman. Les propriétés photocatalytiques des échantillons ont été évaluées pour la réaction d'oxydation du p-chlorophenol dans l'eau. Les résultats obtenus montrent que les traitements de dissolution sélective permettent l'élimination des phases cristallines visées, mais altèrent également, de manière considérable, les propriétés physico-chimiques et photocatalytiques de la phase cristalline résiduelle. Ces effets doivent donc être pris en compte lors des études dédiées aux effets de synergie entre les phases anatase et rutile, notamment pour les photocatalyseurs de type TiO2 reconstruits

Emulsion stabilized with alumina-functionalized mesoporous silica particles

International audienceAlumina-functionalized ordered mesoporous silica SBA-15 particles have been proposed to stabilize Pickering emulsions. Functionalization of SBA-15 particles have been performed by depositing alumina using a two-step synthesis (first, silica condensation, followed by alumina precipitation). Three different Al to Si ratios have been prepared. The calcined materials have been characterized by TEM, SEM, XRD, N2 physisorption, and zeta potential, in order to determine key physicochemical properties, and the alumina localization. The emulsifying and stabilizing properties of the calcined particles have been evaluated for water/toluene-based Pickering emulsions

Prins condensation of isobutylene and formaldehyde over Fe-silicates of MFI structure

The Prins condensation of isobutylene with formaldehyde over iron substituted MFI catalysts has been investigated. The catalysts have been characterized by various methods: TPR for substituted iron, TPD, FTIR, XPS and microcalorimetry for acidity measurements. The catalytic tests show that the medium to weak acid strength of the active sites favors the selectivity to isoprene. A mechanism based on the selective activation of formaldehyde over these centers was proposed to explain the selectivity to isoprene. GaZSM-5 was also tested as a catalyst for this condensation, but its catalytic selectivity is rather close to that of AlZSM-5. In addition, all catalysts demonstrated high activity for the cracking of 4,4-dimethyl-1,3-dioxane, a possible intermediate

Preparation of transition metal (oxide) nanoparticles confined in the secondary pore network of mesoporous scaffolds using melt infiltration

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Synthesis of highly dispersed iron species within mesoporous (Al-)SBA-15 silica as efficient heterogeneous Fenton-type catalysts

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Enhancement of the dispersion and catalytic performances of copper in the hydrogenation of cinnamaldehyde by incorporation of aluminium into mesoporous SBA-15 silica

International audienceCopper is active in hydrogenation reactions, but it is a base metal difficult to disperse inside mesostructured supports, with adverse consequences on the catalytic properties. Incorporating aluminium into mesoporous SBA-15 silicas allows solving both problems of Cu dispersion and activity. The incorporation of 20 wt.% Al2O3 in the SBA-15 host structure leads to an increase of the copper metallic surface area by a factor 6 compared to the pure siliceous SBA-15-supported catalyst. The support also proves to be stable upon exposure to the impregnation aqueous solution used for copper introduction. The incorporation of Al provides Lewis acidic sites that favour the transformation of cinnamaldehyde into cinnamyl alcohol, a feature usually assigned to larger metal particles. As a consequence, the catalytic activity of Cu catalysts is enhanced compared to silica-supported Cu catalysts, while the chemoselectivity towards the unsaturated alcohol appears to be similar to that of a mesoporous alumina-supported system