Effects of the Synthesis Parameters on the Size and Composition of Pt-Sn Nanoparticles Prepared by the Polyalcohol Reduction Method

Platinum-tin alloy nanoparticles with cubic and hexagonal structure have been prepared by the heating up method using metal-acetylacetonates as precursors and 1,2-hexadecanediol as the reducing agent dissolved in dioctyl ether containing oleyl amine and oleic acid as capping agents. The influence of the principal reaction parameters-the concentration of the capping agents, final reaction temperature, reaction time, and ratio of metal precursors-on the size and composition of the Pt-Sn nanoparticles was investigated. Transmission electron microscopy and X-ray diffraction results show that decreasing the amount of capping agents increases not only the size of the nanoparticles but also the extent of alloying. It is proposed that the reaction between the metal precursors is the primary step of the nucleation process leading to Pt-Sn bimetallic particles. In a competitive reaction that depends on the concentration of capping agents, metal oleate complexes are formed. The balance between the rates of these processes affects the relative rates of particle nucleation and growth as well as the composition of the bimetallic nanoparticles. The preparation method described is suitable for controlled formation of Pt-Sn nanoparticles with cubic and hexagonal crystalline structure, which are excellent candidates for investigation of the structure-activity relationship for a number of catalyzed reactions.