Cooperative Catalysis for Selective Alcohol Oxidation with Molecular Oxygen

The activation of dioxygen for selective oxidation of organic molecules is a major catalytic challenge. Inspired by the activity of nitrogen‐doped carbons in electrocatalytic oxygen reduction, we combined such a carbon with metal‐oxide catalysts to yield cooperative catalysts. These simple materials boost the catalytic oxidation of several alcohols, using molecular oxygen at atmospheric pressure and low temperature (80 °C). Cobalt and copper oxide demonstrate the highest activities. The high activity and selectivity of these catalysts arises from the cooperative action of their components, as proven by various control experiments and spectroscopic techniques. We propose that the reaction should not be viewed as occurring at an ‘active site’, but rather at an ‘active doughnut’–the volume surrounding the base of a carbon‐supported metal‐oxide particle.     

Matter of age: growing anisotropic gold nanocrystals in organic media

We investigated the influence of the reduction state of gold ions on the growth of gold nanocrystals in N,N-dimethyl formamide (DMF). While freshly prepared solutions of AuCl3 produce spherical nanocrystals, aged precursor solutions containing mainly Au+ ions and Au(0) atoms lead to various branched nanoparticles. Furthermore, we show that also the amount of the reducing and stabilisation agent tetra-n-octylammonium formate (TOAF) plays a decisive role on the shape of the nanocrystals, allowing us to grow triangular and cubic nanoparticles.     

Hydratation mechanism of a zinc phosphate cement and development of its mechanical profile

The main objective of this study is to understand the setting mechanism of a zinc phosphate cement and the development of its mechanical hardness. This cement is widely used in dentistry and is composed of solid phase cement containing zinc oxide (ZnO) and aluminium phosphate AlPO₄ ·nH₂O, and then liquid phase cement which is composed of phosphoric acid and water. The setting of the cement is due to a mixture of both phases together. In this optic, the control of the effect of different compounds in setting mechanism and hardness is carried out by using several investigation methods such as ESM, XRD, IR, TGA, and DTA. For this study, we explain in detail each phase of the cement process, such as the preparation of raw materials, their mixing, the introduction of the solid phase of cement to the liquid phase, and then the hardening of the cement. The results obtained show the effect of powder size on the setting reaction of the cement and show that aluminium phosphate had an interesting effect on the hardening and setting time of the cement. The X-ray diffraction showed that the principal phase of the hydratation product, which is Hopeïte, is available in the mixture of initial reactants and other secondary products, which are zinc phosphate salts in primary and secondary forms.     

A facile route to ruthenium–carbene complexes and their application in furfural hydrogenation

A number of new N‐heterocyclic carbene (NHC) ligands were synthesized via a multicomponent reaction, wherein an aldehyde or ketone, a primary amine and an α‐acidic isocyanide were reacted, giving the corresponding 2H‐2‐imidazolines. These were easily alkylated with an alkyl halide at position N‐3, yielding the final NHC precursors, that were then complexed with Ru in situ. The resulting complexes are shown to be active and selective catalysts for the transfer hydrogenation of furfural to furfurol, using isopropanol as the hydrogen source. Importantly, the carbene ligand remains coordinated to the ruthenium center throughout the reaction. Copyright © 2009 John Wiley & Sons, Ltd.     

A polyominoes-permutations injection and tree-like convex polyominoes

Plane polyominoes are edge-connected sets of cells on the orthogonal lattice Z², considered identical if their cell sets are equal up to an integral translation. We introduce a novel injection from the set of polyominoes with n cells to the set of permutations of [n], and classify the families of convex polyominoes and tree-like convex polyominoes as classes of permutations that avoid some sets of forbidden patterns. By analyzing the structure of the respective permutations of the family of tree-like convex polyominoes, we are able to find the generating function of the sequence that enumerates this family, conclude that this sequence satisfies the linear recurrence an=6an−1−14an−2+16an−3−9an−4+2an−5, and compute the closed-form formula an=²n+2−(n³−n²+10n+4)/2.     

A simple method for measuring the size of metal nanoclusters in solution

The connection between quantum size effects and the surface plasmon resonance of metal nanoclusters is introduced and the pros and cons of in situ and ex situ cluster analysis methods are outlined. A new method for estimating the size of nanoclusters is presented. This method combines core/shell cluster synthesis, UV-visible spectroscopy, and Mie theory. The core/shell approach enables the estimation of metal cluster sizes directly from the UV-visible spectra, even for transition metal nanoclusters such as Pd that have no distinct surface-plasmon peak in UV-visible region. Pd/Au and Au/Pd core/shell clusters as well as Au-Pd alloy clusters are synthesized and used as test cases for simulations and spectroscopic measurements. The results of the simulations and UV-visible spectroscopy experiments are validated with transmission electron microscopy.