Spectroscopic study of CO adsorption on palladium-ceria catalysts

CO adsorption on palladium-ceria catalysts prepared from Pd acetylacetonate has been investigated by IR and UV-VIS spectroscopies and by volumetric measurements. After calcination and evacuation at 673 K, the samples contain small PdO particles which are immediately reduced upon adsorption of CO at room temperature. For samples prereduced by H-2, electron-donor centres (Ce3+ ions, oxygen vacancies) are created during the pretreatment. These centres are responsible for increased CO adsorption by ceria in the presence of palladium, which leads to apparent CO : Pd values greater than unity and their interaction with palladium induces a carrier-to-metal electron transfer. Plasmon absorption in reducible carriers hinders the detection of species adsorbed on the supported metal.