Chiral rhodium complexes covalently anchored on carbon nanotubes for enantioselective hydrogenation

Chiral rhodium hybrid nanocatalysts have been prepared by covalent anchorage of pyrrolidine-based diphosphine ligands onto functionalized CNTs. This work constitutes the first attempt at covalent anchoring of homogeneous chiral catalysts on CNTs. The catalysts, prepared with two different chiral phosphines, were characterized by ICP, XPS, N2 adsorption and TEM, and have been tested in the asymmetric hydrogenation of two different substrates: methyl 2-acetamidoacrylate and α-acetamidocinnamic acid. The hybrid nanocatalysts have shown to be active and enantioselective in the hydrogenation of α-acetamidocinnamic acid. A good recyclability of the catalysts with low leaching and without loss of activity and enantioselectivity was observed.

Enhancement of the hydrogenation activity of a Pd-tridecilamine (TDA) complex by confinement in carbon nanotubes

An active hydrogenation Pd complex has been immobilised by impregnation on CNTs submitted to several treatments that lead to important differences in their surface chemistry and in the proportion of tubes with both ends open. Most of the hybrid catalysts are more active than the complex in homogeneous phase, but the support properties have an important impact in the catalytic activity. In general, the more developed the surface chemistry, the lower the activity. However, when CNTs are open at both ends, the Pd complex can enter the tubular cavity and an important enhancement of the catalytic activity due to a confinement effect is observed.

Herramientas e indicadores SEO: características y aplicación al análisis de cibermedios

La búsqueda es una de las actividades centrales en el mundo digital y, por tanto, uno de los elementos clave en el análisis de cibermedios, ya que una parte de sus audiencias y de sus ingresos procede de las páginas de resultados de los buscadores (SERP). En este trabajo, presentamos algunas de las herramientas de análisis de posicionamiento SEO más utilizadas con el fin de considerar su aplicación en estudios académicos sobre cibermedios. Aplicamos los nueve indicadores más importantes de estas herramientas a la página principal de cuatro cibermedios generalistas espanoles con el fin de estimar su viabilidad como indicadores alternativos al PageRank y otros indicadores de Google.