Formation of a Pt-Carbonyl Colloid by Reaction of Colloidal Pt with CO

The formation of Pt-carbonyls upon the action of carbon monoxide on colloidal Pt in aqueous media made by the citrate method is investigated. The formation of carbonyls as well as their subsequent reactions are monitored with UV/vis absorption spectroscopy. The Pt-carbonyls formed are aggregates of the well-known Pt-carbonyl family [Pt 3 (CO) 6 ] n 2- with n = 1 to ∼10. The aggregation occurs either with the carbonyl molecules or with small clusters of Pt. A very similar product is formed if H 2 PtCl 6 is treated with CO in aqueous media. The formation of carbonyls from the Pt-colloid does not proceed if the colloid was treated with hydrogen before the action of carbon monoxide. It seems that a prerequisite for the formation of carbonyls is the presence of unreduced Pt-ions adsorbed on the particle surface. The conversion of Pt-colloid into carbonyls proceeds with about 80−90% yield. If the Pt-carbonyl colloid is treated with KOH, formation of isolated [Pt 9 (CO) 18 ] 2- clusters is observed. The kinetics of this reaction is strongly dependent on the amount of added KOH.