Preparation of platinum/carbon aerogel nanocomposites using a supercritical deposition method

Platinum/carbon aerogel (Pt/CA) nanocomposites were synthesized using a supercritical deposition method. Dimethyl(1,5-cyclooctadiene)platinum (II) (CODPtMe2) was dissolved in supercritical CO2 (scCO(2)) and impregnated into porous organic and carbon aerogels. The impregnated aerogels were converted to Pt/CA composites by heat treatment ranging from 300 to 1000 degreesC in the presence of nitrogen gas. Both conventional and high-resolution TEM micrographs showed a good distribution of fairly monodisperse Pt particles throughout the bulk of all the aerogel supports used. The nature and crystallinity of the particles were confirmed using XRD. Increasing the reduction temperature increased both the crystal size and the polydispersity. Crystallite sizes as small as 1 nm were obtained at low reduction temperatures and the particles were single-crystalline. Particle sizes obtained from H-2 and CO chemisorption measurements are consistent with those measured from TEM images, indicating the accessibility of the surface of platinum crystallites. The adsorption isotherm for the scCO(2)-CODPtMe2-CA system was measured at 28 MPa and 80 degreesC and indicated a strong substrate-precursor interaction which was also corroborated by thermogravimetric analyses (TGA). The isotherms also showed that Pt loadings as high as 40 wt % could be achieved. The results of this study demonstrated that in SCF deposition, it is possible to control the dispersion of metal crystallites on various supports through the strength of the interactions between metal precursors and the substrate and the reduction temperature.