Heterogeneous ketonic decarboxylation of dodecanoic acid: studying reaction parameters

Ketonic decarboxylation has gained significant attention in recent years as a pathway to reduce the oxygen content within biomass-derived oils, and to produce sustainable ketones. The reaction is base catalysed, with MgO an economic, accessible and highly basic heterogeneous catalyst. Here we use MgO to catalyse the ketonic decarboxylation of dodecanoic acid to form 12-tricosanone at moderate temperatures (250 °C, 280 °C and 300 °C) with low catalyst loads of 1% (w/w), 3% (w/w) and 5% (w/w) with respect to the dodecanoic acid, with a reaction time of 1 hour under batch conditions. Three different particle sizes for the MgO were tested (50 nm, 100 nm and 44 μm). Ketone yield was found to increase with increasing reaction temperature, reaching approximately 75% yield for all the samples tested. Temperature was found to be the main control on reaction yield, rather than surface area or particle size

Impact of aqueous impregnation on the long-range ordering and mesoporous structure of cobalt containing MCM-41 and SBA-15 materials

International audienceThe effect of modification with cobalt via aqueous impregnation on the structure of MCM-41 and SBA-15 materials was studied using X-ray diffraction (XRD) at low scattering angles and low-temperature nitrogen adsorption. It was shown that the introduction of small amounts of cobalt resulted in dramatic changes in the structure of MCM-41 silica. The low angle XRD peaks characteristic of long-range ordering disappeared while the BET surface area and the total pore volume decreased considerably. Only micropores smaller than 20 Å were detected in the cobalt containing MCM-41 materials. A much smaller impact of impregnation with cobalt on the hexagonal structure and porosity was observed for SBA-15 materials. The periodic structure, surface area and total pore volume of SBA-15 mesoporous silica remained almost unchanged on impregnation with cobalt nitrate, catalyst drying and calcination. Low angle XRD patterns typical of hexagonal structure were still well resolved and intense in the SBA-15 materials containing up to 20 wt. % of cobalt. Analysis of XRD intensities suggested that after aqueous impregnation and drying a considerable amount of cobalt ions was located in the SBA-15 mesopores. Nitrogen adsorption-desorption data indicated plugging a part of SBA-15 mesopores in cobalt containing samples. Due to the high stability, SBA-15 silica appears to have a good potential for its use as a support for metal and oxide catalysts

Quasi-quantitative photo-conversion of methane to ethane at ambient temperature on silver based nanocomposites

International audienc

Quasi-quantitative photo-conversion of methane to ethane at ambient temperature on silver based nanocomposites

International audienc

Quasi-quantitative photo-conversion of methane to ethane at ambient temperature on silver based nanocomposites

International audienc

Characterization of the initial stages of SBA-15 synthesis by in situ time-resolved small-angle X-ray scattering

International audienceThe initial stages of SBA-15 synthesis have been studied by using in situ time-resolved small-angle X-ray scattering with a synchrotron radiation source. The quantitative analysis of X-ray scattering and diffraction intensities allows the structures of intermediates to be identified at the different stages of SBA-15 synthesis. Following tetraethylorthosilicate (TEOS) addition, an intense small-angle scattering and an associated secondary maximum are observed, which are attributed to non-interacting surfactant template micelles encrusted with silicate species. After 25-30 min of the reaction, the broad scattering disappears and narrow Bragg diffraction peaks typical of hexagonally ordered structure are observed. The cylindrical micelles identified from X-ray scattering data appear to be the direct precursors of 2D hexagonal SBA-15 structure. Just after the formation of the SBA-15 hexagonal phase, the cylindrical micelles are only weakly linked in the hexagonal structure. As the synthesis proceeds, the solvent in the void volume between the cylindrical micelles is gradually replaced by more dense silicate species. The unit cell parameter of SBA-15 is progressively decreasing during the SBA-15 synthesis, which can be related to the condensation and densification of silicate fragments in the spaces between the cylinders. The volume fraction of the 2D hexagonally ordered phase is sharply growing during the first 2 h of the reaction. The inner core radius of SBA-15 material remains almost constant during the whole synthesis and is principally affected by the size of the poly(propylene oxide) inner core in the original cylindrical micelles

New insights into the initial steps of the formation of SBA-15 materials: an in situ small angle neutron scattering investigation

International audienceTime-resolved in situ SANS investigations have provided direct experimental evidence for the three initial steps in the formation of the SBA-15 mesoporous material: an induction period is followed by a shape transformation of the micelles from spherical to cylindrical ones followed by the precipitation of a two-dimensional hexagonal phase