The nature of colloidal platinum in aqueous solution: features of catalytic reactions

The specific features of the catalytic reduction of methylviologen by dihyd rogen in water in the presence of platinum colloids synthesized by various methods are studied. The colloids prepared by the radiation-chemical reduct ion of PtCl42- in the presence of polyacrylate or polyphosphate as stabiliz ers and colloids prepared by the reduction with dihydrogen efficiently cata lyze the reaction. The "citrate" colloids synthesized by the reduction of P tCl62- with citric acid are characterized by a prolonged induction period a fter which these colloids also gain the catalytic activity. We assume that the "citrate" platinum colloids are giant clusters with the close-packed me tal core containing the "magic" number of platinum atoms (Pt-561), which ar e coordinated by the ligand molecules blocking the surface of the metal par ticle. In the presence of H-2, the ligand molecules are decomposed or remov ed from the surface, which is accompanied by the appearance of the catalyti c activity.