Synthesis of colloidal particles of poly(2-vinylpyridine)-coated palladium and platinum in organic solutions under the high temperatures and high pressures

Colloidal dispersions of poly(2-vinylpyridine)-coated palladium (Pd) and platinum (Pt) particles in the toluene/1-propanol solution have been synthesized by the decomposition and reduction of palladium acetylacetonate (Pd(acac)2) and platinum acetylacetonate (Pt(acac)2) under the high-temperatures and high-pressures conditions. The size and the structure of the synthesized particles have been examined by transmission electron micrograph (TEM) and extended X-ray absorption fine structure (EXAFS). At 473 K and 25 MPa, colloidal dispersions ([Pd] = 7.5 mM) of Pd particles of 1.9 nm as an average diameter, which had narrow particle size distributions, were synthesized within a few seconds. Pt particles were also synthesized with an average diameter of 2.1 nm. On the other hand, bimetallic Pd/Pt particles were not synthesized at 473-623 K and 25 MPa, probably due to the difference of decomposition rate of each starting compound.