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SSCI-VIDE+CDFA+ASD:NPR:CPI:MBE; International audience; Bimetallic Rh-ReOx (Re/Rh molar ratio 0.4-0.5) catalysts supported on TiO2 and ZrO2 were prepared by the successive impregnation of dried and calcined unreduced supported Rh catalysts. Their catalytic performances were evaluated in the hydrogenolysis of erythritol to butanetriols (BTO) and butanediols (BDO) in aqueous solution at 150-240 degrees C under 30-120 bar H-2. The activity depended on the nature of the support, and the highest selectivity to BTO and BDO at 80% conversion was 37 and 29 %, respectively, in the presence of 3.7 wt% Rh-3.5 wt% ReOx/ZrO2 at 200 degrees C under 120 bar. The characterization of the catalysts by CO chemisorption, TEM with energy-dispersive X-ray spectroscopy, thermogravimetric analysis with MS, and X-ray photoelectron spectroscopy suggests a different distribution and reducibility of Re species over the supported Rh nanoparticles, which depends on the support.

International audience; The aqueous-phase hydrogenolysis of xylitol into glycols over Ru/C was performed in the presence and absence of a wide range of concentrations of Ca(OH)2 to investigate the reaction pathway. Without base, epimerization and cascade decarbonylation were the predominant reactions with high selectivities to C5 and C4 alditols and light alkanes at full conversion. Glycol production was obtained by the addition of Ca(OH)2 to promote the retro-aldol reaction. It competed with reactions without base and became the main reaction for a OH−/ xylitol molar ratio Rmol(OH/xylitol) of 0.13, and high selectivities to glycols (56 %) and glycerol (16 %) were observed. However, lactate was a byproduct at up to 27 % with a high base amount (Rmol(OH/xylitol)=0.68). Bifunctional Ru/metal oxide/C catalysts (metal: Zn, Sn, Mn, Sr, W) were synthesized and were able to cleave the C−C bond into glycols without a base promoter. The 3.1 wt %Ru/MnO(4.5 %)/C catalyst was the most active (220 h−1) with reasonable selectivity to glycols (22 %) and glycerol (10 %) and a low production of lactate (

The application of diastereoselective hydrogenation catalyzed by heterogeneous catalysts for the asymmetric synthesis of organic compounds is illustrated in the reduction of several functional groups. In that approach, the chiral information is provided by the prior attachment of a chiral auxiliary to the substrate to be hydrogenated. The optically active hydrogenated product is then disconnected from the chiral auxiliary. Proper choice of the inductor, of the catalyst and of reaction conditions may result in high diastereoselectivities.

Ultrasound radiation has been recently used for the synthesis of mesoporous materials (MSPM). The main advantages are manifested in the short preparation time and thicker walls leading to a more hydrothermally stable structure.1 This preparation method has already been reviewed.2 The discovery of MSP materials led immediately to the development of many experimental methods for the deposition of materials, especially catalytic materials, into the mesopores. Impregnation, thermal spreading, ion adsorption, and the most recent method3 in which colloidal gold solution is premixed with the precursors for the preparation of the MSPM, are among the methods used for the insertion of materials into the mesopores. Sonochemistry was also employed for this purpose. We will outline in this article the use of the sonochemical processes for the insertion of nanomaterials into the pores of MSPM. We will explain how this process is conducted, to what extent the materials are deposited in the pores and what is the mechanis...

The diastereoselective hydrogenation of 2-methyl nicotinic acid covalently bound to proline ester or pyroglutamic ester over supported metallic catalyst yielded moderate diastereoselectivity (26%). The hydrogenation of the corresponding pyridinium salt was studied and similar de's were achieved.

The diastereoselective hydrogenation of o -toluic acid or o -methoxy benzoic acid covalently bound to different chiral auxiliaries was performed on Rh and Ru supported catalysts. The cis- isomers were formed predominantly, with a diastereoselectivity largely influenced by the structure of the chiral inductor and the steric hindrance brought for the preferential adsorption of one face of the aromatic substrate. The effect of the functional group on the proline auxiliary (alcohol or ester groups susceptible to modify the anchoring of the aromatic substrate) was weak. Hydrogenolysis occurred rather extensively with the methoxy benzoic acid and constituted the most important hydrogenation pathway on Rh/C. The presence of the CO group in the pyroglutamic acid methyl ester is a determining factor for obtaining good diastereoselectivity.