Deposition of Pt, Pd, Ru and Au on the surfaces of titanate nanotubes

Nanoparticles of different metals (Pt, Pd, An) or a metal hydroxide (Ru) have been immobilized on the surface of mesoporous titanate nanotubes produced by alkali hydrothermal treatment of TiO2, and have been characterized by HRTEM. Two different approaches have been utilised for the deposition of metal particles into the internal pores of titanate nanotubes: (i) deposition from solution confined inside the nanotubes and (ii) blocking the external surface of the nanotubes. A third method, ion-exchange of protons onto metal cations in titanate nanotubes followed by reduction or alkali treatment (in the case of Ru hydroxide), has been used for deposition of metal nano-particles on both the internal and external surfaces of the nanotubes. Nanoparticles of metal or metal hydroxide deposited by the ion-exchange method are characterised by an average size in the range of 1.2-5 nm, and deposits are uniformly distributed on the surface, resulting in a very high loading density. An increase in the amount of deposited metal resulted predominantly in a higher nanoparticle loading density, without growth in the particle size. This was correlated with the retention of high specific catalytic activity of ruthenium hydrated oxide deposited on titanate nanotubes in the reaction of selective oxidation of benzyl alcohol over a wide range (0.6-8.7 wt%) of ruthenium loading. The methods for metallization of titanate nanotubes are critically discussed.