Preparation of carbon black supported Pd, Pt and Pd–Pt nanoparticles using supercritical CO 2 deposition

Abstract

The preparation of carbon black (Black Pearl 2000) supported single Pd, Pt and bimetallic Pd–Pt nanoparticles utilizing the supercritical CO 2 deposition method was investigated. Palladium (II) acetylacetonate (Pd(acac) 2) and dimethyl (cyclooctadiene) platinum (II) (Pt(cod)me 2) were utilized as metallic precursors. The adsorption isotherms of Pd(acac) 2 and Pt(cod)me 2 on BP2000 in scCO 2 at 20 MPa and 60 °C were determined. A mass transfer model was found to represent the experimental data on the kinetics of adsorption of Pd(acac) 2 onto BP2000 in scCO 2 fairly well with a fitting error of 5.6%. In order to prepare the supported nanoparticles, chemical reduction with H 2 in scCO 2 was utilized. Increasing reduction temperature and metal loading caused an increase in Pd particle size. The Pd particles were irregularly distributed and the size range of the particles was 3–100 nm, whereas Pt nanoparticles were homogeneously distributed with a size range of 2–6 nm. Binary metal nanoparticles could also be produced by simultaneous adsorption and subsequent reduction of the precursors. It was found that addition of Pt increased the homogeneity and reduced the particle size on the support compared to single Pd nanoparticles. From the X-ray spectrometry data, it was seen that there was a heterogeneous mixture of the bimetallic nanoparticles. Pt-rich nanoparticles had diameters of around 4 nm, whereas Pd-rich nanoparticles were larger with diameters of around 10 nm.