Sophie Hermans

Nanotechnology in catalysis

Nanotechnology and Heterogeneous Catalysis.- Oxide-Supported Metal Thin-Film Catalysts: The How and Why.- Developing Catalytic Nanomotors.- Catalysis by Gold: Recent Advances in Oxidation Reactions.- Gold Catalysts Supported on Nanostructured Materials: Support Effects.- Highly Effective Nanocatalysts Prepared Through Sol-Gel Technique.- Dendrimer Templates for Supported Nanoparticle Catalysts.- Tungsten Oxide Nanorods: Synthesis, Characterization, and Application.- Catalysis by Metal and Oxide Nanoparticles, Single Metal Atoms and Di-Nuclear Oxo-Ions in Zeolites.- A Dual Catalytic Role of Co Nanoparticles in Bulk Synthesis of Si-Based Nanowires.- Influence of Particle Size and Interaction with the Support on Redox and Catalytic Properties of Metals, Metal Oxides, and Metal Complexes.- Thermo-Catalytic Oxidation of Dihydroxybenzenes in the Presence of Nanoparticle Iron Oxide.- Synthesis of Palladium-Based Supported Catalysts by Colloidal Oxide Chemistry.- Gold-Based Nanoparticle Catalysts for Fuel Cell Reactions.- Carbon-Supported Core-Shell PtSn Nanoparticles: Synthesis, Characterization and Performance as Anode Catalysts for Direct Ethanol Fuel Cell.

Solvent-free, low-temperature, selective hydrogenation of polyenes using a bimetallic nanoparticle Ru-Sn catalyst

The point of attachment of bimetallic Ru6Sn particles which are anchored to the pore walls of a highly dispersed high-area mesoporous silica is found to be the tin atom, as indicated by in situ and ex situ measurements. This catalyst displays high activity for the low-temperature, selective hydrogenation of cyclic polyenes under solvent-free conditions (see scheme).

Single-Step, Highly Active, and Highly Selective Nanoparticle Catalysts for the Hydrogenation of Key Organic Compounds

Pores for cluster catalysts: Nanoparticles of both Ru5Pt and Ru10Pt2, uniformly distributed along the inner walls of mesoporous silica, exhibit high catalytic performance in the single-step hydrogenation of dimethyl terephthalate (DMT, to 1,4-cyclohexanedimethanol (CHDM); see scheme), of benzoic acid (to cyclohexane carboxylic acid), and of naphthalene (in the presence of sulfur) to cisdecalin.

New catalysts for clean technology

The preparation, characterisation and catalytic performance of both bimetallic nanoparticles and chiral homogeneous catalysts anchored along the interior walls of mesoporous silica (MCM-41) are described. The bimetallic nanoparticles are prepared from Ru 6Pd 6 and Ru 6CSn carbonyl clusters and the resulting MCM derivatives are characterised by a number of methods, including EXAFS, FTIR and STEM. The solvent-free hydrogenation of naphthalene and cyclic polyenes using these catalysts are described, with the Ru 6CSn based catalyst giving a 90% selectivity for the corresponding monoenes while the Ru 6Pd 6 produces the fully hydrogenated product in high yield. The homogeneous catalysts 1-[-(R)-1′2-bis(diphenylphosphino)ferrocenyl] ethyl-N-N′-dimethylethylenediamine palladium dichloride was heterogenised by anchoring along the inside walls of MCM-41. The catalysed reaction between cinnamylacetate and benzylamine was studied and the catalyst produced 51% of the branched chain product possibly with 100%ee.

High-resolution imaging of nanoparticle bimetallic catalysts supported on mesoporous silica

Although conventional high‐resolution transmission electron microscopy is a powerful method for the elucidation of the structure of mesoporous solids (diameter of pores from 1.5 to 20 nm), it is far less capable than high‐resolution scanning transmission electron microscopy in identifying the spatial distribution of nanocrystals of catalysts encapsulated within the mesopores. Using high‐angle annular dark‐field imaging (either in a 100 or 300 keV STEM system), it is possible to locate precisely individual bimetallic nanoparticles (Ag3Ru10, Cu4Ru12 and Pd6Ru6 hydrogenation catalysts) supported on mesoporous silica, to determine their size distribution, and to record their characteristic X‐ray emission maps. It is also established that there is little tendency for elemental fragmentation of the bimetallic catalysts, all of which were prepared by decarbonylating, by thermolysis, precursor cluster carbonylate anions: [Ag3Ru10C2(CO)28Cl]−, [Ru6C(CO)16Cu2Cl]2− and [Ru6Pd6(CO)24]2−.

Catalysis with gold complexes immobilised on carbon nanotubes by π-π Stacking interactions: Heterogeneous catalysis versus the boomerang effect

A new pyrene-tagged gold(I) complex has been synthesised and tested as a homogeneous catalyst. First, a simple 1,6-enyne was chosen as a model substrate for cyclisation by using different solvents to optimise the reaction conditions. The non-covalent immobilisation of our pyrene-tagged gold complex onto multi-walled carbon nanotubes through π-π stacking interactions was then explored to obtain a supported homogeneous catalyst. The heterogenised catalyst and its homogeneous counterpart exhibited similar activity in a range of enyne cyclisation reactions. Bearing in mind that π-π interactions are affected by temperature and solvent polarity, the reuse and robustness of the supported homogeneous catalyst was tested to explore the scope and limitations of the recyclability of this catalyst. Under the optimised conditions, recyclability was observed by using the concept of the boomerang effect.

Bismuth-palladium heterometallic carboxylate as a single-source precursor for the carbon-supported Pd-Bi/C catalysts.

The heterometallic complex [Bi(2)Pd(2)(O(2)CCF(3))(10)(HO(2)CCF(3))(2)] (1) was obtained by the solid state reaction of Bi(III) trifluoroacetate/trifluoroacetic acid adduct with unsolvated trinuclear Pd(II) trifluoroacetate. The crystal structure of 1 consists of discrete tetranuclear molecules, in which two paddlewheel [BiPd(O(2)CCF(3))(4)] units are connected by two chelating-bridging trifluoroacetate ligands through bismuth ends. There are no metal-metal bonds in the tetrameric structure of 1, since both Bi...Pd (3.0843(4) A) and Bi...Bi (4.5074(4) A) distances are too long to be considered as bonding interactions. A study of the solution behavior revealed that not only the coordinated trifluoroacetic acid in 1 can be effectively replaced by other donor solvent molecules but also the tetranuclear complex can be cleaved in solution into discrete dinuclear Bi-Pd species. Complex 1 was used as precursor for the preparation of a bimetallic Pd-Bi carbon-supported catalyst. The preparation procedure included the modification of the carbon support to increase the number of oxygenated functions at its surface followed by grafting complex 1 via ligand exchange for surface carboxylates and activating thermally. The resulting catalyst, consisting of small supported metallic particles, was found to be more active than the reference materials prepared from multisource homometallic Pd and Bi precursors.

Preparation and characterisation of a highly active bimetallic (Pd–Ru) nanoparticle heterogeneous catalyst†

The mixed-metal carbonylate cluster [Pd6Ru6(CO)24]2– was used as a single-source precursor in the synthesis of a highly active hydrogenation catalyst (stoichiometry PdRu) which has been characterised by electron microscopy and X-ray absorption spectroscopy: PdRu readily hydrogenates alkenes and naphthalene (the latter predominantly to cis- decalin) under mild conditions

Radical addition of xanthates on carbon nanotubes as an efficient covalent functionalization method

Radical-initiated support: Xanthates were used as chemical reagents for the sidewall covalent functionalization of carbon nanotubes (see figure). The best grafting yields were obtained with stoichiometric ratios of xanthate and the radical initiator lauroyl peroxide. One grafted function was used as a tether for bimetallic cluster compounds, which were converted into very small (1-2 nm) supported nanoparticles upon heating.

Frequency selective microwave absorption induced by controlled orientation of graphene-like nanoplatelets in thin polymer films

Highly ordered polycarbonate films containing parallel graphite nanoplatelets have been produced by squeezing the corresponding random nanocomposites in the melt. Orientation of the conductive fillers is observed in the plane of the film, i.e., perpendicular to the squeezing direction. It only appears above a critical concentration of 15 wt. % and results from a confinement effect. Oriented samples show a resonance-like sharp increase of the conductivity at a given frequency in the microwave region, with the possibility to control the value of this frequency and the resulting absorption by changing the nanoplatelets concentration. Above this frequency, the oriented polymer nanocomposites show a high level of electromagnetic absorption, which opens the possibility to tailor materials with effective electromagnetic interference shielding by absorption in selected frequency ranges. The in-plane stacking of conductive nanoplatelets separated by insulating polymer induces their strong capacitive coupling to the signal propagating in the plane of the polymer film. As a result, the equivalent circuit of this propagation becomes a resonant system composed of capacitors, inductors, and resistors, which agrees well with the experimental results.