Carbon nanofiber-supported platinum catalysts were studied to establish the influence of the support surface composition on their performance in the liquid-phase hydrogenation of cinnamaldehyde. By acid-base titration, XPS, and TGA-MS, the number of oxygen-containing surface groups was determined in oxidized carbon nanofiber samples and in platinum catalysts pretreated at 473-973 K. TEM, EXAFS, and H-2-chemisorption studies showed the presence of a narrow and stable platinum particle-size distribution (1-2 nm). The overall catalytic activity increased by a factor of 25 after treatment at 973 K, which is tentatively related to the decreasing amount of oxygen of the carbon fibers. With XPS and H-2-chemisorption experiments carried out at 308 K no clear evidence was found for a change in the electronic structure of the platinum particles induced by the oxygen-containing groups present on/in the surface of the carbon nanofibers. A linear decrease of the hydrogenation activity with an increase of the number of acidic groups on the carbon nanofiber support was found. Therefore, it is suggested that hydrogenation is assisted by adsorption of cinnamaldehyde on the carbon support after removal of the oxygen-containing surface groups. (C) 2004 Elsevier Inc. All rights reserved.