MONODISPERSED COLLOIDAL METAL PARTICLES FROM NONAQUEOUS SOLUTIONS - CATALYTIC BEHAVIOR IN HYDROGENOLYSIS AND ISOMERIZATION OF HYDROCARBONS OF SUPPORTED PLATINUM PARTICLES

Platinum catalysts have been prepared by depositing on alumina monodispersed particles of platinum prepared in reversed micellar solution. After deposition, the particles are well dispersed on the support and the size distribution has a sharp maximum around 2 nm. The isomerization and hydrogenolysis of hexanes were studied in order to get more information about the particle size effects on the selectivities of Pt catalysts in these reactions. It was found that this catalyst exhibits the same selectivities as a low dispersed ordinary platinum catalyst. These selectivity values are quite different from the ones given by a highly dispersed classical catalyst in spite of the fact that the catalysts have fairly similar average particle size. Such results confirm the conclusions previously proposed that isomerisation via cyclic mechanism and non selective hydrogenolysis of hexanes take place only on platinum particles smaller than 1 nm.