Heck and Suzuki–Miyaura couplings catalyzed by nanosized palladium in polyaniline

A novel route to prepare polyaniline (PANI)‐supported Pd(0) nanoparticles by a one‐pot chemical route is presented. Nanosized Pd(0) particles were first prepared by reduction of Pd(OAc)₂ using t‐BuONa activated sodium hydride in refluxing THF. A ligand exchange with aniline on t‐BuONa‐stabilized Pd(0) particles yielded aniline‐stabilized particles. Pd(0)/PANI nanocomposites were finally obtained by polymerizing aniline‐stabilized Pd(0) particles using ammonium persulfate. Nanocomposites were characterized by transmission electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy. Results show that this one‐pot experimental route is successful in producing hybrid materials constituted of Pd(0) nanoparticles stabilized by PANI due to the strong binding of PANI amine groups to Pd(0) particles. TEM images of the nanohybrids show that metal particles with diameters of ca. 4.9 nm are homogeneously dispersed in PANI. The preliminary results indicate that the Pd(0) particles supported on PANI behave as efficient heterogeneous catalysts in the Heck and Suzuki–Miyaura reactions of aryl iodides. Copyright © 2005 John Wiley & Sons, Ltd.     

Sol-Gel Transition and Structural Evolution on Multicomponent Gels Derived from the Alumina-Silica System

The capacity of the sol-gel process of producing highly pure, homogeneous alumina-silica based materials had been demonstrated in the last few years. However, a full understanding on the mechanisms associated to sol formation and sol to gel transition has not yet been achieved and is required for the development of a new generation of nano-structurally tailored materials that will significantly enhance the technological importance of the sol-gel process. In this work, tetraethyl orthosilicate (TEOS) and aluminum isopropoxide were used to prepare materials within the entire silica-alumina system. Process parameters, such as gelation time, were correlated to variables of the initial stage of the process, such as pH, temperature of hydrolysis and water/alkoxide ratio. The obtained gels were dried at 105°C and subsequently heat treated at 500 and 1100°C for 3 hours. X-ray diffraction and infrared spectroscopy were used to characterize the materials and phase transformations. Structural information obtained from phase characterization and phase transformations was correlated to the effects of the process variables on sol formation and gelation, providing insights related to the mechanisms involved. The influence of temperature of aluminum isopropoxide hydrolysis on peptization and gelation of the mixtures was noted. The different behavior of mixtures hydrolyzed at low and high temperatures was suggested to be caused by different mechanisms of surface charge formation on the structurally different aluminum hydroxides. Monophasic and diphasic mullite xerogels were produced by changing temperature of aluminum isopropoxide hydrolysis, and led to formation of mullite and Al−Si spinel phases respectively, when treated at 1100°C.     

Optimisation du couplage entre une source et un faisceau de fibres optiques à l'aide d'un programme de tracé de rayons

This paper presents a study of the coupling between a source and a fibre bundle. A ray trace numerical simulation was used to examine the effects of geometrical and optical parameters of the concentrator and the fibre bundle. We compare the results of the computer program with measurements obtained in the case of a light emitting diode and a single lens.     

Solitons and poles in the nonlinearity parameter

The KdVN-soliton solutions are analysed in terms of the perturbation parameter λ which governs the nonlinearity. They are generated by rational Stieltjes functionsQ ^(N) (λ), each pole of which can be associated with a soliton. The asymptotic emergence of the separate solitons follows at once from the motion of the poles along the negative real λ-axis. Successive diagonal Padé approximants ofQ ^(N) (λ) are considered. They provide a class of approximate solutions with a striking semisoliton like behaviour.     

Adsorption and surface structural chemistry of Na and Na + O2 on Ag(110)

The adsorption of Na and the coadsorption of Na and O₂ on Ag(110) have been studied by LEED, thermal desorption, and Auger spectroscopy. For Na coverages in the regime 0 < θ_Na < 2 the Na desorption spectra show a single peak (β) corresponding to a desorption energy of ～195 kJ mol^?1, and at θ_Na ～ 2 a (1 × 2) LEED pattern appears. At still higher coverages (2 < θ_Na < 5), a (1 × 3) surface phase is formed, and a new peak (α) appears in the desorption spectra; this is identified with Na desorption from an essentially Na surface. The desorption energy of αNa (～174 kJ mol^?1) indicates that Na adatoms beyond the first chemisorbed layer are significantly influenced by the presence of the Ag substrate. The initial sticking probability of O₂ on Na-dosed Ag(110) is enormously enhanced over the clean surface value, being of the order of unity, and O₂ chemisorption ultimately leads to a (4 × 1) surface structure. The presence either subsurface Na alone, or of both Na and O below the surface, causes substantial changes in surface behaviour. In the former case, submonolayer doses of Na lead to the appearance of a (1 × 2) structure; and in the latter case, Na + O₂ coadsorption results in a c(4 × 2) structure. Auger spectroscopy indicates that the Ag(110)-c(4 × 2)$\text{Na}\text{O}$ phase forms with a constant stoichiometry which is independent of the initial Na dose. The Na:O ratio in this adlayer is believed to be of the order of unity. The structures of the various ordered phases, the nature of the AgNa bonding, and the interatomic spacing between the alkali adatoms on Ag(110) are discussed.     

Repeated quadrature using derivatives of the integrand

Zusammenfassung Es werden neue Formeln mitgeteilt für die Auswertung wiederholter Integrale der Form , wof(x) entweder analytisch oder als Werttabelle gegeben ist. Die Genauigkeit dieser Formeln wird mit derjenigen von bereits vorhandenen Methoden verglichen.