One weight percentage PdO/SnO2 and 0.1 wt.% Na-1 wt.% PdO/SnO2 catalysts have been synthesized through a sol-gel route and these catalysts have been characterized by XRD, BET, SEM and temperature-programmed adsorption and desorption techniques with regard to their activity for the CO oxidation reaction. CO adsorption and CO-O-2 co-adsorption followed by O-2 TPD have been carried out to observe the role of sodium promotion on the catalytic activity. The catalytic activity of PdO/SnO2 catalysts is suppressed by blockage of CO active sites by O-2 on co-adsorbed catalysts. Sodium-promoted catalysts possess increased affinity to oxygen and thus, exhibit superior activity Upon CO-O-2 co-adsorption, but these catalysts have been observed to perform poorly upon consecutive adsorption of CO and O-2. The effect has been ascribed to enhanced interaction of sodium-promoted surfaces with CO hindering oxygen adsorption on CO precovered surface. (c) 2004 Elsevier B.V. All rights reserved.