The present work studies the influence of the surface chemistry of carbon supports on the electrochemical behaviour of Pd and Au-Pd core-shell (CS) nanoparticles. Vulcan XC-72R was chemically modified by different acid treatments, inducing changes in the volume of the mesopores and surface density of oxygenated species. The CS nanostructures featuring 19 nm Au cores and 10 nm Pd shells were synthesized by colloidal methods and subsequently incorporated to the carbons supports. Pd nanoparticles were prepared by impregnating a Pd precursor into the modified carbons followed by reduction with sodium borohydride. The use of different preparation methods allowed the independent study of the effect of the support on the morphology/distribution of the nanoparticles and on the reactivity of the nanoparticles, through their interaction with organic molecules. The electrocatalysts were characterised by XRD, EDX, Raman spectroscopy and contact angle measurements. CO and formic acid (HCOOH) electro-oxidation were studied using cyclic voltammetry and chronoamperometry. The effect of the carbon support on the electrocatalytic activity was highly dependent on the method of preparation. Pd nanoparticles obtained by impregnation showed higher HCOOH oxidation currents when supported on the highly oxidised Vulcan support. This is due to the generation of smaller particle sizes (2.3 nm) as a result of the high density of oxygenated functional groups. On the other hand, the CS nanostructures are significantly less active in highly oxidised Vulcan as a results of specific chemical interactions which may be related to the formation of oxides. The implication of these findings towards rationalising particle substrate interactions are briefly discussed. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.