Nitrogen-doped graphene stabilized copper nanoparticles for Huisgen [3+2] cycloaddition "click" chemistry

Yves Leterrier, Véronique Michaud, Sravendra Rana, Monika Srivastava
ROYAL SOC CHEMISTRY, 2019
Article

Résumé

Nitrogen-doped reduced graphene oxide (NRGO) stabilized copper nanoparticles are designed to assist Cu(I)-catalyzed Huisgen [3+2] cycloaddition "click" chemistry (CuAAC). This study demonstrates a robust route for the synthesis of vastly dispersed heterogeneous catalysts (NRGO/Cu2O), achieving CuAAC at low temperaturewithout any external additive (oxidizing/reducing agent) with high stability and recyclability. Underlying mechanisms are analysed using DFT calculations, confirming the experimental results.

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https://infoscience.epfl.ch/record/267024?ln=fr

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Pd Nanoparticles in a Supported Ionic Liquid Phase: Highly Stable Catalysts for Selective Acetylene Hydrogenation under Continuous-Flow Conditions

Paul Joseph Dyson, Lioubov Kiwi, Gabor Laurenczy, Marina Ruta

Monodispersed Pd nanoparticles of 5 and 10 nm were obtained via reduction of Pd(acac)2 dissolved in ionic liquid (IL), [bmim][PF6], or [bmimOH][TF2N], supported on carbon nanofibers (CNF) anchored to sintered metal fibers (SMF). Using [bmimOH][TF2N], the monodispersed Pd nanoparticles were synthesized by simple heating in the absence of an additional reducing agent. The supported ionic liquid phase Pd nanoparticles on the structured CNF/SMF composites were tested for the selective hydrogenation of acetylene to ethylene and showed excellent long-term stability. The IL cation-anion network surrounding the nanoparticles suppressed the formation of active-site ensembles, known to catalyze the oligomerization of acetylene, responsible for the catalyst deactivation. The reaction rate was controlled by the internal diffusion of the reactants through the IL phase. The solubility of acetylene and ethylene in [bmim][PF6] was analyzed by NMR spectroscopy, which showed an order of magnitude difference. The lower solubility of ethylene compared to acetylene in the IL results in a high selectivity to ethylene, up to 85% at 150 °C. The catalytic system also demonstrated high efficiency and long-term stability without any deactivation in ethylene-rich feed (2 vol % of acetylene, 40 vol % of ethylene, 10 vol % of H2 in Ar), and therefore, the system shows promise for industrial application.

2008

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Catalyst design for selective hydrogenations is of major importance for the manufacturing of fine chemicals. Catalytic procedure which uses scarce and expensive noble metals is very challenging in terms of exclusive attack of a single functionality or substituent. The approach taken in this thesis is based on rational catalyst design that calls on a combination of catalyst synthesis and characterization. This has been applied for the design of catalysts suitable for industrially relevant reactions, i.e. the partial catalytic reduction of substituted nitroaromatic compounds and alkynes. Molybdenum nitrides were selected as they represent a more sustainable alternative to noble metals, less expensive and easy to prepare. First, beta-Mo2N was used to catalyze the liquid phase selective hydrogenation of a series of para-substituted nitroarenes to give the corresponding aromatic amine. Incorporation of low amounts (0.25% wt.) of Au nanoparticles on beta-Mo2N enhanced hydrogen uptake and catalytic activity while delivering an ultraselective response. In a second step, the influence on the catalytic response of nitride crystallographic phase (beta- vs. gamma-Mo2N) and surface area (7-66 m2 g-1) was examined. Both phases promoted the exclusive hydrogenation of p-chloronitrobenzene to p-chloroaniline where the beta-form delivered a higher specific (per m2) rate; the one for gamma-Mo2N was independent of surface area. The inclusion of Au on both nitrides served to enhance p-chloroaniline production. Finally, it was shown that incorporation of N in Mo structure can increase nitrobenzene hydrogenation rates on Mo2N samples with higher nitrogen content. In contrast, -C=O hydrogenolysis was favored with benzaldehyde as a result of lower N content. As a powerful tool for tailoring metal nanoparticle morphology, colloidal methods were used to design structured catalysts effective for the selective alkyne and âNO2 group reduction. The development of a catalyst based on polyvinylpyridine modified structured carbon nanofibers on sintered metal fibers supported (4 nm) polyvinylpyrrolidone (PVP) stabilized Pd was shown to be an optimum formulation for acetylene semi-hydrogenation where the catalyst shows high selectivity (93%) and stability with time-on-stream. We have established that reducing agent does not play a critical role in catalytic response while steric (vs. electronic) stabilizers and larger colloidal metal crystallites are more efficient. PVP-stabilized Ni nanocrystals were also prepared via colloidal method and tested in the m-dinitrobenzene hydrogenation were an antipathetic structure sensitivity was recorded. TOF and selectivity to m-nitroaniline exhibited a marked dependency on the presence of the stabilizer. It was attributed to preferential adsorption of PVP on selective edge and vertex atoms, leaving the plane atoms free. Supporting the Ni nanoparticles on activated carbon fibers and removing traces of PVP by a UV-ozone treatment resulted in a dramatic increase in selectivity to target m-NAN even at high conversions. Two-sites Langmuir-Hinshelwood kinetic model has been applied to rationalize the results. In summary, this thesis demonstrates that the product distribution can be controlled on a nano-level by tuning the properties of the active phase through modifications of the structural parameters (allotropic form, composition), modifications on the nanoparticle microenvironment (organic ligand shell) and optimization of particle size.

EPFL2015

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EPFL2015