Chemisorption-XRD particle size discrepancy of carbon supported palladium: Carbon decoration of Pd?

A systematic discrepancy is often observed between chemisorption versus X-ray diffraction and/or electron microscopy-determined nanoparticle size estimates for metals supported on carbon. It is hypothesized that lower than expected chemisorption capacity is due to decoration of the metal surface by the carbon support. To test this, a series of carbon supported Pd nanoparticles with different pretreatments was prepared and analyzed using Temperature Programmed Oxidation. Carbon oxidation peaks distinct from high temperature bulk carbon burn off were observed for all samples at around 250 degrees C and 300 degrees C. A short oxidation at the latter temperature appears to remove the decorating layer as the TPO peaks disappear and the reduced metal surface chemisorbs at close to the expected capacity. (C) 2014 Elsevier B.V. All rights reserved.