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.

Hybrid catalysts based on carbon nanotubes and nanofibres.

Hybrid catalysts have been prepared by the immobilization of a Rh complex on carbon nanotubes and nanofibres. To tether the complex, a siloxane type bond has been created by reaction of a trimetoxisilane end of a ligand and -OH phenol type groups on the supports surface. The hybrid catalysts have been tested in the hydrogenation of three different substrates: cyclohexene (as a test for activity), carvone (to analyze the chemoselectivity) and 2-metyhl acetamidoacrylate (to evaluate enantioselectivity, using BINAP as chiral ligand). The obtained results show that the hybrid catalysts are more active than the homogeneous complex. The enhanced activity has been related to a confinement effect, produced as a consequence of the metal complex location inside the tubular structures of the supports. The enantioselectivity is opposite for the heterogenized and the homogeneous complex. Some differences have been found between the properties of catalysts prepared with nanotubes and nanofibres, which have been related to differences in the tube inner diameter.

Solid-phase synthesis of graphitic carbon nanostructures from iron and cobalt gluconates and their utilization as electrocatalyst supports.

We present a novel and facile synthesis methodology for obtaining graphitic carbon structures from Fe(II) and Co(II) gluconates. The formation of graphitic carbon can be carried out in only one step by means of heat treatment of these organic salts at a temperature of 900 degrees C or 1000 degrees C under inert atmosphere. This process consists of the following steps: (a) pyrolysis of the organic gluconate and its transformation to amorphous carbon, (b) conversion of Fe(2+) and Co(2+) ions to Fe(2)O(3) and CoO and their subsequent reduction to metallic nanoparticles by the carbon and (c) conversion of a fraction of formed amorphous carbon to graphitic structures by Fe and Co nanoparticles that act as catalysts in the graphitization process. The removal of the amorphous carbon and metallic nanoparticles by means of oxidative treatment (KMnO(4) in an acid solution) allows graphitic carbon nanostructures (GCNs) to be selectively recovered. The GCNs thus obtained (i.e. nanocapsules and nanopipes) have a high crystallinity as evidenced by TEM/SAED, XRD and Raman analysis. In addition, we used these GCNs as supports for platinum nanoparticles, which were well dispersed (mean Pt size approximately 2.5-3.2 nm). Most electrocatalysts prepared in this way have a high electrocatalytical surface area, up to 90 m(2) g(-1) Pt, and exhibit high catalytic activities toward methanol electrooxidation.