Switching intermolecular interactions by confinement in carbon nanotubes

The encapsulation of trityl-functionalised C60 molecules inside carbon nanotubes drastically affects the intermolecular interactions for this species. Whilst the orientations of molecules in the crystal are often controlled by thermodynamics, the molecular orientations in nanotubes are a result of kinetic control imposed by the mechanism of entry into and encapsulation within the nanotube

MOF-based heterogeneous catalysis in continuous flow via incorporation onto polymer-based spherical activated carbon supports

We present an approach to harnessing the tuneable catalytic properties of complex nanomaterials for continuous flow heterogeneous catalysis by combining them with the scalable and industrially implementable properties of carbon pelleted supports. This approach, in turn, will enable these catalytic materials, which largely currently exist in forms unsuitable for this application (e.g. powders), to be fully integrated into large scale, chemical processes. A composite heterogeneous catalyst consisting of a metal–organic framework-based Lewis acid, MIL-100(Sc), immobilised onto polymer-based spherical activated carbon (PBSAC) support has been developed. The material was characterised by focused ion beam-scanning electron microscopy-energy dispersive X-ray analysis, powder X-ray diffraction, N2 adsorption, thermogravimetric analysis, atomic absorption spectroscopy, light scattering and crush testing with the catalytic activity studied in continuous flow. The mechanically robust spherical geometry makes the composite material ideal for application in packed-bed reactors. The catalyst was observed to operate without any loss in activity at steady state for 9 hours when utilised as a Lewis acid catalyst for the intramolecular cyclisation of (±)-citronellal as a model reaction. This work paves the way for further development into the exploitation of MOF-based continuous flow heterogeneous catalysis

Efficient Hydrogen Evolution from Dimethylamine Borane, Ammonia Borane and Sodium Borohydride Catalyzed by Ruthenium and Platinum Nanoparticles Stabilized by an Amine Modified Polymer Immobilized Ionic Liquid: a Comparative Study

Platinum and ruthenium nanoparticles stabilised by an amine modified polymer immobilised ionic liquid (MNP@NH2-PEGPIILS, M = Pt, Ru) catalyse the hydrolytic liberation of hydrogen from dimethylamine borane (DMAB), ammonia borane (AB) and NaBH4 under mild conditions. While RuNP@NH2-PEGPIILS and PtNP@NH2-PEGPIILS catalyse the hydrolytic evolution of hydrogen from NaBH4 with comparable initial TOFs of 6,250 molesH2.molcat−1.h−1 and 5,900 molesH2.molcat−1.h−1, respectively, based on the total metal content, RuNP@NH2-PEGPIILS is a markedly more efficient catalyst for the dehydrogenation of DMAB and AB than its platinum counterpart, as RuNP@NH2-PEGPIILS gave initial TOFs of 8,300 molesH2.molcat−1.h−1 and 21,200 molesH2.molcat−1.h−1, respectively, compared with 3,050 molesH2.molcat−1.h−1 and 8,500 molesH2.molcat−1.h−1, respectively, for PtNP@NH2-PEGPIILS. Gratifyingly, for each substrate tested RuNP@NH2-PEGPIILS and PtNP@NH2-PEGPIILS were markedly more active than commercial 5wt % Ru/C and 5wt% Pt/C, respectively. The apparent activation energies of 55.7 kJ mol−1 and 27.9 kJ mol−1 for the catalytic hydrolysis of DMAB and AB, respectively, with RuNP@NH2-PEGPIILS are significantly lower than the respective activation energies of 74.6 kJ mol−1 and 35.7 kJ mol−1 for its platinum counterpart, commensurate with the markedly higher initial rates obtained with the RuNPs. In comparison, the apparent activation energies of 44.1 kJ mol−1 and 46.5 kJ mol−1, for the hydrolysis NaBH4 reflect the similar initial TOFs obtained for both catalysts. The difference in apparent activation energies for the hydrolysis of DMAB compared with AB also reflect the higher rates of hydrolysis for the latter. Stability and reuse studies revealed that RuNP@NH2-PEGPIILS recycled efficiently as high conversions for the hydrolysis of DMAB were maintained across five runs with the catalyst retaining 97% of its activity

Amine-modified polyionic liquid supports enhance the efficacy of PdNPs for the catalytic hydrogenation of CO₂ to formate

Palladium nanoparticles stabilised by aniline modified polymer immobilised ionic liquid is a remarkably active catalyst for the hydrogenation of CO₂ to formate; the initial TOF of 500 h⁻¹ is markedly higher than either unmodified catalyst or its benzylamine and N,N-dimethylaniline modified counterparts and is among the highest to be reported for a PdNP-based catalyst

Selective Partial Reduction of Nitroarenes to the Hydrazoarene Catalyzed by Amine‐Modified Ordered Mesoporous Silica Immobilized Ionic Liquid (OMSIIL) Stabilised RuNPs

Ruthenium nanoparticles stabilised by an amine-modified Ordered Mesoporous Silica Immobilized Ionic Liquid (OMSIIL) are efficient catalysts for the partial reduction of nitrobenzene to hydrazobenzene with 100 % selectivity as well as the complete reduction to aniline. High selectivity for the partial reduction of nitrobenzene to hydrazobenzene was obtained when the reaction was conducted in ethanol with 0.5 mol% catalyst and NaBH₄ as the hydrogen donor whereas aniline was obtained as the sole product in water when dimethylamine borane (DMAB) was used as the hydrogen donor. Interestingly, while a range of electron poor nitroarenes were reduced to the corresponding hydrazoarene with high selectivities and good conversions, nitroarenes substituted with electron donating groups resulted in complete reduction to the aniline. Composition-time profiles suggest that reductions conducted in ethanol with sodium borohydride occur via the condensation pathway while those conducted in water using dimethylamine borane as the hydrogen source may well go via the direct pathway. This is the first example of the selective reduction of nitrobenzene to hydrazobenzene using a ruthenium nanoparticle-based catalyst and the initial TOF of 320 mol nitrobenzene converted mol Ru⁻¹ h⁻¹ for the partial reduction of nitrobenzene to hydrazobenzene is markedly higher than previous literature reports. A study of the catalyst performance as a function of the surface modification revealed that each component has a direct and dramatic effect on the efficacy as RuNPs stabilised by COK-12 modified with imidazolium-based ionic liquid and a primary amine gave the highest conversion while selective removal of either component or replacement of the primary amine with a tertiary amine resulted in a marked reduction in efficiency

Stable isotope food-web analysis and mercury biomagnification in polar bears ( Ursus maritimus )

Mercury (Hg) biomagnification occurs in many ecosystems, resulting in a greater potential for toxicological effects in higher-level trophic feeders. However, Hg transport pathways through different food-web channels are not well known, particularly in high-latitude systems affected by the atmospheric Hg deposition associated with snow and ice. Here, we report on stable carbon and nitrogen isotope ratios, and Hg concentrations, determined for 26, late 19th and early 20th century, polar bear ( Ursus maritimus ) hair specimens, collected from catalogued museum collections. These data elucidate relationships between the high-latitude marine food-web structure and Hg concentrations in polar bears. The carbon isotope compositions of polar bear hairs suggest that polar bears derive nutrition from coupled food-web channels, based in pelagic and sympagic primary producers, whereas the nitrogen isotope compositions indicate that polar bears occupy > fourth-level trophic positions. Our results show a positive correlation between polar bear hair Hg concentrations and δ 15 N. Interpretation of the stable isotope data in combination with Hg concentrations tentatively suggests that polar bears participating in predominantly pelagic food webs exhibit higher mercury concentrations than polar bears participating in predominantly sympagic food webs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73930/1/j.1751-8369.2009.00114.x.pd