The adsorption and catalytic properties of Pt/SnO2 were investigated as a model catalyst system that undergoes strong chemical interaction upon reduction-oxidation treatment. The surface platinum on Pt/SnO2 adsorbed very little CO at room temperature after reduction with hydrogen at 400 degrees C. This chemical interaction was found to be related with the reaction between precious metal and reduced tin oxide support. The Pt/SnO2 particles after reduction treatment were composed of a core/shell structure where the core of Pt was covered with an oxide shell. An X-ray diffraction pattern of Pt/SnO2 sample after reduction at 400 degrees C contained some lines attributed to intermetallic compounds, such as PtSn2 and PtSn4. The Pt/SnO2 catalyst was employed for a fuel electrode of a polymer electrolyte fuel cell and compared with the conventional Pt/C catalyst. Both catalysts were degraded with the presence of CO in hydrogen. However, the degradation of Pt/SnO2 with 100 ppm CO was insignificant as compared with that of Pt/C. (c) 2005 Elsevier B.V. All rights reserved.