Study the liquid-phase Beckmann rearrangement on the surface of SBA-15-SO3H catalyst

Hybrid inorganic-organic solid acid material SBA-15-Ph-SO3H was synthesized by the co-condensation of tetraethoxysilane and 2-(4-chlorosulfonylphenyl) ethyltrimethoxysilane in the presence of a Poly (alkylene oxide) block copolymer under acid conditions. The catalytic activity of the obtained materials was studied in liquid-phase Beckmann rearrangement of cyclohexanone oxime to epsilon-caprolactam. The results show that there exists an obvious "Solvent effect" in this reaction system and the strong Bronsted acid is proofed again to be at the origin of the formation of epsilon-caprolactam. Moreover, we tentatively proposed a reaction mechanism involving a five-member ring intermediate product when toluene was used as solvent

Reduced forms of Rh(III) containing MCM-41 silicas as hydrogenation catalysts for arene derivatives

International audienceRhodium containing mesoporous siliceous materials with MCM-41 pore architecture have been prepared via a template directed hydrolysispolycondensation of tetraethoxysilane and rhodium(III) chloride in aqueous ammonia. The effect of aging and hydrothermal conditions on rhodium incorporation and on the porous structure of the resulting solids has been examined using elemental analysis, powder X-ray diffraction (XRD), N2 sorption measurements and transmission electron microscopy (TEM). Optimized synthetic conditions afforded MCM-41 materials with Si/Rh 1400 and 120. Subsequent reduction of rhodium oxides species by hydrogen emphasized that the growth of Rh0 particles (2–3 nm) is controlled by the porosity of the support. The conditions and efficiency of this step were evaluated through H2-TPR (temperature programmed reduction) and IR monitored CO adsorption studies. The resulting materials showed a good catalytic activity and stability in the hydrogenation of arene derivatives under mild pressure and temperature. Cis/trans selectivity of dimethylcyclohexanes was discussed in the light of dispersion measurements

Infrared investigations of arenesulfonic modified mesoporous materials by the use of complementary probes

Arenesulfonic mesoporous materials [SBA(R), 0.05 a parts per thousand currency sign R (incorporation ratio) a parts per thousand currency sign0.15] have been prepared by the co-condensation of tetraethoxysilane (TEOS) and 2-(4-chlorosulfonylphenyl) ethyltrimethoxysilane (CSPTMS) in acidic solutions of Pluronic P123. The extent of the surface functionalisation and the nature of the interactions between sulfonic groups and the surface in SBA(0.05) and SBA(0.15) samples were investigated by FT-IR spectroscopy using two probes of different basic strengths. It was shown that carbon monoxide (CO, at 77 K) can be used as a good probe to study the surface functionalisation through the nu(C=O) vibration at 2,158 cm(-1) corresponding to its interaction with free silanol groups. Ammonia (NH3, at 423 K) is able to disturb the strong interactions of Si-OH-H3OS by forming the delta(NH)-NH4 (+) which allowed to emphasise that SO3H groups of the less functionalised material SBA(0.05) are less acidic since the number of the acid groups is less important than in SBA(0.15)

Investigation of the catalytic activity of extracted and smoothly calcined arenesulfonic modified SBA-15 materials

International audienceA thorough FTIR investigation of the thermal stability of arenesulfonic modified SBA-15 solids revealed that most of the organic functional groups are preserved until 400 ◦C. These results have been confirmed by the thermogravimetric analyses of the corresponding materials calcined at 200 ◦C (EC-200) or 400 ◦C (EC-400), respectively. Such studies showed that the smoother calcination procedure (200 ◦C) is appropriate in order to complete the removal of Pluronic P123 in the extracted sample (E). Moreover, it can be noticed that such calcination treatment did not alter tremendously the catalytic performances of the resulting solids. Both E and EC-200 materials exhibited high activities in the liquid phase condensation of 2-methylfuran with acetone and in the decomposition of cumene hydroperoxide into phenol

Influence of acid–base properties of Mg-based catalysts on transesterification: role of magnesium silicate hydrate formation

International audienceThe transesterification reaction assisted through heterogeneous basic catalysis was thoroughly studied because of its importance in transforming biomass, as for biodiesel production or lactone opening. As catalysts with the strongest basic properties are not always the most efficient ones, a series of magnesium-based materials, exhibiting a large range of acido–basic properties, was investigated. Moreover, in order to compare gas and liquid phases operating conditions, a model reaction (transesterification of ethyl acetate with methanol) was chosen. It appears that gas phase transesterification (at 393 K) requires strong basic sites, whereas magnesium silicate, exhibiting moderate basicity together with acidic properties, is a very reactive catalyst in the liquid phase (at 333 K) depending on its preparation method. The set of experimental data (XRD, XPS, DRIFTS, MEB, 29Si and 25Mg NMR) demonstrated that a magnesium silicate hydrate structure (MSH) is formed at the surface of the most active silicates. It is thus concluded that different mechanisms operate under gas and liquid conditions, and that among the magnesium silicate materials, the MSH phase exhibits specific acido–basic properties beneficial to this kind of reaction

Complementarity of Density Functional Theory and Nuclear Magnetic Resonance Tools To Probe the Nano-Layered Silicates Surface Chemistry and Morphology

International audienceBy combining experimental, spectroscopic, structural, and physical characterizations and extensive density functional theory simulations, unprecedented insight is gained on the local surface properties of synthetic talc nanoparticles, their structure, morphology and particle size distribution. Basically, the nuclear magnetic resonance (NMR) chemical shifts profiles of these nano-layered silicates were dissected thoroughly and revealed the existence of bulk and surface contributions in the 1H and 29Si spectra. Beyond the fact that significant knowledge has been acquired on the overall structure of the synthetic talc nanoparticles (mixture of defective and non-defective layers, with defects rejected on the external interfaces), the highlighting of these signals enabled us to access the average morphologies and particle sizes of the samples by decomposing the 29Si NMR profiles into Lorentzian contributions. Finally, the particle size distributions in number were also described in terms of a log-normal law. These distributions were compared to the particle sizes obtained from X-ray diffraction (XRD), Brunauer–Emmett–Teller measurements (BET), and dynamic light scattering (DLS) methods. The distributions of gyration radii determined by DLS are shown to match the distributions in size consistent with the same morphology

Biomass characterization and biogas production of pretreated straw: is there a correlation?

International audienceBiomass characterization and biogas production of pretreated straw: is there a correlation

Discrimination of Surface and Bulk Structure of Crystalline Hydroxyapatite Nanoparticles by NMR

Solid state ¹H and ³¹P NMR spectroscopy was used to characterize well-crystallized hydroxyapatite samples of different stoichiometry prepared by a precipitation route. The aim of the paper was to investigate the bulk structural features of samples with different stoichiometry and to discriminate signals related to the surface from those related to the bulk. Thanks to the implementation of (i) in situ thermal pretreatment at 623 K, (ii) filling of the NMR rotor in a controlled atmosphere, (iii) relative proton enrichment of the surface performed under controlled isotopic H-D exchanges, and (iv) specific NMR sequences including inversion recovery measurements, two-dimensional HETCOR and DQSQ spectra, new resolved NMR signals originating from the surface and from the bulk were identified alongside already reported signals associated with adsorbed water, structural phosphates, and OH groups. In particular, considering the influence of the stoichiometry, it was possible to identify a specific signature associated with defective hydrogenophosphate groups present in the bulk. Despite the well-ordered surface terminations of the nanoparticles, specific surface signals associated with nonprotonated and protonated surface terminating phosphate groups could be identified. In addition, from the three resolved ¹H signals associated with columnar OH channels, two from the bulk and one from the surface, a structural model describing the relative organization of hydroxyl groups running along the <i>c</i> axis inside the columnar OH channel in the well-crystallized particles is proposed: the two types of bulk hydroxyls are associated with the presence of both up and down orientations of their related protons in a same tunnel. Corresponding ¹H signatures of the surface-terminating hydroxyls or structured water molecules emerging from the OH channels were also identified. Moreover, in addition to the broad 5.1 ppm line associated with water adsorbed on calcium cations and hydrogenophosphate groups, the 1.1 ppm line is ascribed to structured external water molecules stacking in continuity to the OH channels

Identification of ebselen as a potent inhibitor of insulin degrading enzyme by a drug repurposing screening

International audienceInsulin-degrading enzyme, IDE, is a metalloprotease implicated in the metabolism of key peptides such as insulin, glucagon, β-amyloid peptide. Recent studies have pointed out its broader role in the cell physiology. In order to identify new drug-like inhibitors of IDE with optimal pharmacokinetic properties to probe its multiple roles, we ran a high-throughput drug repurposing screening. Ebselen, cefmetazole and rabeprazole were identified as reversible inhibitors of IDE. Ebselen is the most potent inhibitor (IC50 (insulin) = 14 nM). The molecular mode of action of ebselen was investigated by biophysical methods. We show that ebselen induces the disorder of the IDE catalytic cleft, which significantly differs from the previously reported IDE inhibitors. IDE inhibition by ebselen can explain some of its reported activities in metabolism as well as in neuroprotection