Mesoporous Pt-SiO2 and Pt-SiO2-Ta2O5 Catalysts Prepared Using Pt Colloids as Templates

International audienc

Batch versus flow stereoselective hydrogenation of α-acetamido-cinnamic acid catalyzed by an Au(I) complex

International audienceA chiral gold (I) (2S,4S)-1-tert-butoxycarbonyl-4-diphenylphosphino-2-(diphenylphosphino- methyl) pyrrolidine (BPPM) complex has been prepared using [Au(SMe2)Cl] as precursor. The heterogenization of the Au-BPPM catalyst onto the CNT support followed two routes, ie (i) the non-covalent immobilization of the gold(I)complex by dry-impregnation, and (b) covalent immobilization of the gold(I)complex on a pre-functionalized CNT. These catalysts afford the stereoselective hydrogenation of α-acetamidocinnamic acid to the (R)-N-acetyl-phenylalanine enantiomer. The nature of the solvent affected both the enantioselectivity and TOFs. Among MeOH, EtOH, and TFE, methanol appeared to be the most efficient one (at 80 °C a TOF of 0.37 h−1 for a total enantioselectivity to the R-isomer). Transferring the reaction in the flow reactor, under similar conditions (methanol, room temperature) led to a 10 time increase of the TOF with no change in the stereoselectivity. The decrease of the TOF in time for both the reference Rh and the Au catalysts was assigned to their partial modification under the reaction conditions. The heterogenization of the Au-BPPM catalyst onto the CNT support, for the same content of Au-complex, led to a very important increase of the conversion with no change in the selectivity. However, the covalent bonding was more efficient affording a very high increase of the conversion even at room temperature (95% after 24 h), thus demonstrating that the anchoring a support increases the dispersion, and in consequence the efficiency. These CNT-Au-BPPM catalysts preserved the catalytic performances during recycling as also confirmed by the characterization results

Direct oxidation of amines to nitriles in the presence of ruthenium-terpyridyl complex immobilized on ILs/SILP

Ru2Cl4(az-tpy)2 was immobilized within a range of supported ionic liquids on silica. SILP operates as an efficient heterogeneous catalyst in oxidation of long chain linear primary amines to corresponding nitriles.</p

DES-Based Biocatalysis as a Green Alternative for the l-menthyl Ester Production Based on l-menthol Acylation

The deep eutectic solvent (DES)-based biocatalysis of l-menthol acylation was designed for the production of fatty acid l-menthyl ester (FME) using fatty acid methyl ester (FAME). The biocatalytic reaction was assisted by a lipase enzyme in the DES reaction medium. &#1410;&#1362;-menthol and fatty acids (e.g., CA&mdash;caprylic acid; OA&mdash;oleic acid; LiA&mdash;linoleic acid; and LnA&mdash;linolenic acid) were combined in the binary mixture of DES. In this way, the DES provided a nonpolar environment for requested homogeneity of a biocatalytic system with reduced impact on the environment. The screening of lipase enzyme demonstrated better performance of immobilized lipase compared with powdered lipase. The performance of the biocatalytic system was evaluated for different DES compositions (type and concentration of the acid component). l-menthol:CA = 73:27 molar ratio allowed it to reach a maximum conversion of 95% methyl lauric ester (MLE) using a NV (Candida antarctica lipase B immobilized on acrylic resin) lipase biocatalyst. The recyclability of biocatalysts under optimum conditions of the system was also evaluated (more than 80% recovered biocatalytic activity was achieved for the tested biocatalysts after five reaction cycles). DES mixtures were characterized based on differential scanning calorimetry (DSC) and refractive index analysis

Influence of gold particle size on the photocatalytic activity for acetone oxidation of Au/TiO(2) catalysts prepared by dc-magnetron sputtering

Two series of Au/TiO2 materials with different gold content have been prepared by dc-magnetron sputtering on ceramic shaped pure anatase or Degussa P25 TiO2. The time of deposition was varied between 1 and 20 min in order to obtain different thickness and nanoparticle size of the gold films. For comparison samples with Au loadings in the range 0.3–0.9 wt% were prepared using the deposition–precipitation methodology. The obtained materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), DR-UV-Vis and atomic force and scanning electron microscopy techniques. The photocatalytic activity was checked in the photo-oxidation of acetone under both UV and visible irradiation conditions. Several factors were found to influence the photoactivity. An optimal Au content corresponding to a maximum activity is observed and attributed to the occurrence of adequate titania surface coverage and Au particle size. The support plays an important role and it was found that pristine anatase on which gold (average particle size 7.7 nm) was deposed by dc-reactive sputtering exhibits the maximum of the activity. Samples prepared by dc-sputtering were more active than samples prepared by deposition–precipitation method. Also, the photocatalysts prepared using dc-reactive sputtering showed activity under both UV and visible light irradiation, while those prepared using the deposition–precipitation technique are active only under UV light. The most likely mechanism of gold activation of titania is that upon light absorption, gold nanoparticles inject electrons into the titania conduction band.The authors kindly acknowledge NATO's Scientific Affairs Division in the framework of the Science for Peace Programme Sfp 981476 for the financial support. Bogdan Cojocaru wish to thank CNCSIS PNII PD 13/2010 for financial support.Cojocarua, B.; Neatu, S.; Sacaliuc-Pârvulescu, E.; Lévy, F.; Pârvulescua, VI.; García Gómez, H. (2011). Influence of gold particle size on the photocatalytic activity for acetone oxidation of Au/TiO(2) catalysts prepared by dc-magnetron sputtering. Applied Catalysis B: Environmental. 107(1):140-149. doi:10.1016/j.apcatb.2011.07.007S140149107

Impact of structured catalysts in amine oxidation under mild conditions

A structured graphene/graphite catalyst grown on a commercial austenitic stainless steel sheet providing a micromonolith was obtained by submitting the nude stainless steel structure to a carbon-rich atmosphere (first 300 mL/min of a reductive H/N (1:1) flow, then to 180 mL/min of a CH/H (1:5)) at high temperature (900 °C) for 2 h. The preparation procedure resulted in a homogenous surface coated with a carbon-rich film as observed by EDX and SEM images. Further characterizations by Raman spectroscopy revealed characteristic Raman lines of graphene and crystalline graphite disposed in a hierarchical organization. The disposal of the obtained surface layers was also confirmed by grazing incidence X-ray diffraction. Besides this, XRD indicated the overlapping diffraction lines of graphite, cementite and MC carbides. The graphene nature of the outermost layer was also confirmed by XPS. The catalytic behavior of the structured graphene/graphite catalyst was evaluated in the selective oxidation of heptylamine. At 200 °C it afforded a total conversion with a combined selectivity in heptanonitrile and N-heptylidene-heptylamine of 67% (10% heptanonitrile) that corresponds indeed to a very efficient system in the absence of any metal. Kinetic experiments with the scope to calculate the activation energies were also performed.The authors gratefully acknowledge the financial support from the 275/2011PN-II-ID-PCE-2011-3-0060 project and from Spanish Ministerio de Economía y Competitividad (MINECO) project ENE2013-47880-C3-2-R, co-financed by FEDER funds from the European Union. J.L. Santos also acknowledges the Spanish Ministerio de Economía y Competitividad for his predoctoral fellowship (BES-2014-068244)

An Advanced Approach for MgZnAl-LDH Catalysts Synthesis Used in Claisen-Schmidt Condensation

Using organic-base tetramethylammonium hydroxide (TMAH) is a viable, cheap, and fast option for the synthesis of MgZnAl-LDH-type materials by both co-precipitation and mechano-chemical methods. TMAH presents several advantages, such as the smaller quantity of water required in the washing step compared to the use of inorganic alkalis, the prevention of LDH contamination with alkali cations, and its action as a template molecule in texture tailoring. It also has disadvantages, such as its presence in small quantities in the resulting layered materials. Regardless of the use of organic/inorganic bases and co-precipitation/mechano-chemical methods, zincite stable phase was found in all the synthesized solids. The basicity of catalysts followed the trend: mixed oxides > reconstructed > parent LDH. The memory effect of LDH was supported only by the presence of Mg and Al cations, while Zn remained as a zincite stable phase. The catalytic activities for Claisen-Schmidt condensation of benzaldehyde with cyclohexanone provided values higher than 90% after 2 h, with a total selectivity toward 2,6-dibenzylidenecyclohexanone, while self-condensation of cyclohexanone yielded no more than 7.29% after 5 h. These behaviors depended on catalyst basicity as well as on the planar rigidity of the compound