Emmanuelle Teuma

Synthesis of Platinum–Ruthenium Nanoparticles under Supercritical CO2 and their Confinement in Carbon Nanotubes: Hydrogenation Applications

Bimetallic platinum–ruthenium nanoparticles stabilised by pyridine‐ and monophosphine‐based ligands were prepared either in supercritical CO2 or in THF. TEM analyses evidenced a tendency of the nanoparticles prepared in supercritical CO2 to agglomerate. Both types of bimetallic nanoparticles were further confined into functionalised multiwalled carbon nanotubes. Upon confinement, PtRu nanoparticles stabilised by phosphine ligands appeared more agglomerated than those stabilised by the pyridine ligand. These materials were applied to cinnamaldehyde hydrogenation. Confined PtRu nanoparticles showed higher catalytic activity and selectivity than unsupported nanoparticles.

A smart palladium catalyst in ionic liquid for tandem processes

New catalytic systems based on in situ and preformed palladium nanoparticles in ionic liquids (characterised by TEM) starting from palladium acetate or dipalladiumtris(dibenzylideneacetone) have been applied in the synthesis of 4-phenylbutan-2-one (II), a model compound for the preparation of fragrances. Imidazolium-based ionic liquid containing a methyl hydrogenophosphonate anion leads to an efficient Pd-catalyzed tandem coupling/reduction process, taking advantage of the multi-role of this solvent (nanoparticles stabiliser, base, hydrogen transfer agent). The influence of the mono-phosphine ligands (1-3) on the catalyst has been evaluated, showing that the ligand-free palladium system turns into the most appropriate for the formation of II using Pd(OAc)(2) as precursor. Fine-tuning conditions involved in this multi-parameter process have led us to propose a plausible mechanism based on the hydrogen transfer coming from the methyl hydrogenophosphonate anion.

Palladium nanoparticles stabilised by cinchona-based alkaloids in glycerol: efficient catalysts for surface assisted processes

Palladium nanoparticles (PdNPs) were synthesised and fully characterised, both in solution and the solid state, using naturally-occurring cinchona-based alkaloids in neat glycerol. These nano-systems were stable under reaction conditions, finding applications in hydrogenation and hydrodehalogenation processes, as a result of their surface-like behaviour. Their reactivity was improved in relation to that involving PdNPs stabilised by phosphines and also by Pd/C as a heterogenous catalyst, mainly in terms of recyclability. In particular, the colloidal palladium catalyst stabilised by quinidine was highly efficient to promote the hydrodechlorination of aromatic compounds under low dihydrogen pressure. These original catalysts found applications in the synthesis of secondary and tertiary amines including N-substituted anilines, by means of one-pot tandem Pd-catalysed methodologies under smooth conditions. In all of these processes, glycerol performed a crucial function as a liquid support for the immobilisation of nanoparticle-based catalysts, allowing both the stabilisation of the nano-catalysts and easy recycling of the catalytic phase.