Sol-gel prepared PdO/SnO2 and Na-PdO/SnO2 catalysts were investigated by X-ray photoelectron spectroscopy (XPS), diffuse reflectance IR (DRIFTS), temperature-programmed reaction spectroscopy (TPRS) and impulse techniques. Alkali-metal promotion was observed to enhance CO oxidation rate and decreases light-off temperatures of PdO/SnO, XPS analysis revealed that alkali-metal promotion resulted in the segregation of Pd atoms and promoted the oxygen storage capacity of the catalysts. The presence of super-oxide species was also observed over Na-PdO/SnO2 catalyst and the formation of a relatively stable ternary oxide of sodium and palladium (NaxPd3O4) was postulated. Surface titration experiments utilizing pulse technique showed that alkali-metal-promoted sample was able to preserve part of its CO oxidation activity even after reduction pretreatment and that oxygen diffusion from bulk of the catalyst effectively promoted the activity of Na-PdO/SnO2 sample at 150 degrees C. (c) 2005 Elsevier B.V. All rights reserved.