In 'structure sensitive' catalytic reactions there is an ideal size and morphology for the metal particles on the catalyst surface for optimum reaction conditions. If a 'monomodal distribution' could be produced, the less effective particles could be excluded and the metal used more efficiently. A narrow particle size distribution gives them a very high surface area, better for catalytic activity and good order (1). Work has been done on chemical routes to achieve this; for instance, IBM has patents describing narrow size distributions in nanoparticles produced by decomposition of metal salts and complexes (2).

In the latest literature, workers in Singapore and Zhejiang, China, have produced uniform platinum (Pt) nanoparticles of average diameter ~ 3 nm and good dispersion on carbon nanotubes by a microwave-heating polyol process. The nanoparticles have a sharp size distribution with high dispersion on the C nanotubes surface. Higher catalytic activity for methanol electrooxidation at room temperature than a commercial platinum catalyst was demonstrated (3).

Workers in Lanzhou, China, have produced highly-ordered well-dispersed Pt colloidal nanoparticles by reducing H₂PtCl₆ with hydrogen using PVP as a stabilising agent. When used as Pt/glassy carbon electrodes, for absorbed CO oxidation, with particle size < 1 nm, the particles demonstrated high activity (4).

In Japan (5), workers found that Pt clusters (1–3 nm) embedded in C particles diffused through the covered amorphous C layer on heating above 1200ºC. The clusters were three times more stable at high temperatures than commercial Pt clusters on carbon.

In China, monodisperse palladium (Pd) nanoparticles (6) of size < 5 nm with a 10% size distribution were produced with a hypophosphite reducing agent. The Pd nanoparticles formed a well-ordered 2D array. Other reducing agents gave no observeable size change, but wide size distribution. Different capping agents altered stability, self-organised patterns, and solubility.

Workers in Italy, found novel Pt-Ru nanoparticles on C substrates could be reproducibly prepared using metal-organic precursors under vacuum at low temperatures. The nanoparticles were homogeneously dispersed, had narrow size distribution (~ 2 nm) and were efficient at methanol electrooxidation (7).