Franck Launay

New Ti-SBA mesoporous solids functionnalized under gas phase conditions: characterisation and application to selective oxidation of alkenes

Functionnalization of mesoporous silica SBA15 with titanium oxide was carried out under gas phase conditions with TiCl4 as titanium source, between 473 and 673 K, followed by hydrolysis at ambient temperature. Spectroscopic characterisations (X-ray diffraction, XPS, IR, UV-Vis.) and porosimetry measurements showed that part of TiO2 is grafted on the internal surface of the pores. Catalytic activity was tested in selective oxidation of bulky alkenes. Several cycles of reaction showed that any leaching of Ti species is observed in the liquid phase.

Green and selective epoxidation of alkenes catalysed by new TiO2–SiO2 SBA mesoporous solids

New catalysts TiO2–SiO2 (Ti–SBA) with pore sizes of 37 and 65 A have been synthesized by grafting titanium on a structured mesoporous SBA15 (SBA for Santa BArbara and 15 for hexagonal structure) by means of titanium tetrachloride in the gas phase. These catalysts have been tested in the selective epoxidation of cyclooctene, cyclohexene, (R)-limonene and α-pinene. Whatever the oxidant, hydrogen peroxide (H2O2), tert-butyl hydroperoxide (TBHP) or cumyl hydroperoxide (CHP), the selectivity is 100%. However, the yield is low with H2O2 and the catalyst is partially leached out. In the case of TBHP and CHP the epoxide yields can reach practically 100% and no leaching of titanium is observed after four successive reaction cycles. An effect of pore size on the epoxidation kinetics of α-pinene and cyclooctene has been found.

A surfactant-assisted preparation of well dispersed rhodium nanoparticles within the mesopores of AlSBA-15: characterization and use in catalysis

Well dispersed and efficient Rh(0) hydrogenation catalysts were obtained by the reduction of Rh(III)-exchanged mesoporous aluminosilicates by sodium borohydride in the presence of N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl) ammonium chloride.

Chiral ammonium-capped rhodium(0) nanocatalysts: synthesis, characterization, and advances in asymmetric hydrogenation in neat water.

Optically active amphiphilic compounds derived from N-methylephedrine, N-methylprolinol, or cinchona derivatives possessing bromide or chiral lactate counterions were efficiently used as protective agents for rhodium(0) nanoparticles. The full characterization of these surfactants and the obtained nanocatalysts was performed by means of different techniques. These spherical nanoparticles, with sizes between 0.8-2.5 nm depending on the stabilizer, were evaluated in the hydrogenation of model substrates in neat water as a green solvent. The rhodium catalysts showed relevant kinetic properties, but modest enantiomeric excess values of up to 13 % in the hydrogenation of ethyl pyruvate. They were also investigated in the hydrogenation of disubstituted arenes, such as m-methylanisole, providing interesting catalytic activities and a preferential cis selectivity of around 80 %; however, no asymmetric induction was observed.

Efficiency of Polyoxometalate-Based Mesoporous Hybrids as Covalently Anchored Catalysts

Polyoxometalate (POM) hybrids have been covalently immobilized through the formation of amide bonds on several types of mesoporous silica. This work allows the comparison of three POM-based mesoporous systems, obtained with three different silica supports in which either the organic functions of the support (amine vs carboxylic acid) and/or the structure of the support itself (SBA-15 vs mesocellular foams (MCF)) were varied. The resulting POM-based mesoporous systems have been studied in particular by high resolution transmission electronic microscopy (HR-TEM) in order to characterize the nanostructuration of the POMs inside the pores/cells of the different materials. We thus have shown that the best distribution and loading in POMs have been reached with SBA-15 functionalized with aminopropyl groups. In this case, the formation of amide bonds in the materials has led to the nonaggregation of the POMs inside the channels of the SBA-15. The catalytic activity of the anchored systems has been evaluated through the epoxidation of cyclooctene and cyclohexene with H2O2 in acetonitrile. The reactivity of the different grafted POMs hybrids has been compared to that in solution (homogeneous conditions). Parallels can be drawn between the distribution of the POMs and the activity of the supported systems. Furthermore, recycling tests together with catalyst filtration experiments during the reaction allowed us to preclude the hypothesis of a significant leaching of the supported catalyst.

Oxidative ring opening of epoxides by tert-butyl hydroperoxide in the presence of AISBA-15

Oxidative ring opening of epoxides by tert -bytyl hydroperoxide was carried out in the presence of AISBA-15 under mild conditions (acetonitrile, 353 K). Various materials were prepared with different Si/Al molar ratio (5 to 20) in order to compare their catalytic activity. These solids were fully characterized especially by 27 Al NMR and NH 3 adsorption. This work emphasizes the influence of the method used for the incorporation of aluminium (grafting (AISBA(PS)) or direct synthesis (AlSBA(DS))) on the conversion of cyclohexene oxide to adipic acid. The best yields of the diacid (40–50%) were obtained in the presence of aqueous TBHP and AlSBA(DS) materials.

Transition-Metal-Free Catalysts for the Sustainable Epoxidation of Alkenes: From Discovery to Optimisation by Means of High Throughput Experimentation

Transition-metal-free oxides were studied as heterogeneous catalysts for the sustainable epoxidation of alkenes with aqueous H₂O₂ by means of high throughput experimentation (HTE) techniques. A full-factorial HTE approach was applied in the various stages of the development of the catalysts: the synthesis of the materials, their screening as heterogeneous catalysts in liquid-phase epoxidation and the optimisation of the reaction conditions. Initially, the chemical composition of transition-metal-free oxides was screened, leading to the discovery of gallium oxide as a novel, active and selective epoxidation catalyst. On the basis of these results, the research line was continued with the study of structured porous aluminosilicates, gallosilicates and silica-gallia composites. In general, the gallium-based materials showed the best catalytic performances. This family of materials represents a promising class of heterogeneous catalysts for the sustainable epoxidation of alkenes and offers a valid alternative to the transition-metal heterogeneous catalysts commonly used in epoxidation. High throughput experimentation played an important role in promoting the development of these catalytic systems.

Mesoporous silica encapsulating Rh(0) colloids: structure and catalytic properties

Colloidal metallic precursors have been used successfully to prepare new rhodium(0) supported mesoporous catalysts. The aqueous dispersion of Rh(0) previously synthesized was added either (i) to preformed mesoporous silica (MCM-41 or SBA-15) or (ii) to the gel mixture used for the solid synthesis. The different materials have been characterized by TEM, N2 adsorption-desorption, PXRD and elemental analysis. All the solids, especially those obtained by the direct route, reveal well-organized mesoporous structures. Their catalytic activity was investigated in the hydrogenation of aromatic ring (conversion of styrene into ethylcyclohexane) and was shown to be better in hexane than in ethanol. The solids prepared by impregnation of MCM-41 and SBA-15 with Rh(0) colloids (pathway (i)) afforded the best yields of ethylcyclohexane (up to 100% in hexane and 72% in ethanol, respectively).

Comparative study of the catalytic activity of Al-SBA-15 and Ga-SBA-15 materials in α-pinene isomerisation and oxidative cleavage of epoxides

Materials of the SBA-15 type with well dispersed Ga or Al atoms were prepared successfully by using different procedures (direct synthesis or grafting). Depending on the heteroelement sources, gallium-based samples displayed different catalytic activities in the isomerisation of α-pinene but led to better selectivities than Al-solids did. However, these last ones turned out to be more adapted to the formation of adipic acid (AA) by the oxidative cleavage of cyclohexene oxide (CHO) in the presence of tert-butylhydroperoxide (TBHP).

Production and Characterization of Activated Carbon from Orange Peels by Chemical Activation with Sulfuric Acid

Oranges represent 75% of the total citrus fruits (Guiza in Ecol Eng, 99: 134–140, 2017) throughout the world, and Tunisia is one of the major juice producers. Orange peels could cause a significant disposal problem but they are also valuable biomass wastes (Valdes et al. in Langmuir 18: 2111–2116, 2002; Fang et al. in Electrochim Acta 50: 3616–3621, 2005; He et al. in J Surg Oncol 102: 676–682, 2010).