The sensitivity and selectivity of SnO 2-based gas sensors could be improved by doping of small amount of noble metals. In this work, we used X-ray photoelectron spectroscopy to investigate Pd particles evaporated on the SnO 2 thin layers, prepared by spray pyrolysis. We compared the binding energy and initial state variations as a function of Pd coverage. CO–Pd interaction was investigated using the C 1s photoelectron spectra that exhibited two CO-related components. The dissociation activity was monitored as a rise of C 1s signal at 285 eV while the molecularly adsorbed CO exhibited the peak intensity at 287 eV.