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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.