Pd–Ce interactions and adsorption properties of palladium: CO and NO TPD studies over Pd–Ce/Al2O3 catalysts

We have examined the adsorption of CO and NO on powder Pd/Al2O3, Pd–Ce/Al2O3 and CeO2/Al2O3 catalysts, using temperature-programmed desorption (TPD). For CO adsorption on oxidized and pre-reduced Pd–Ce/Al2O3 TPD profiles are identical to those observed for Pd/Al2O3, suggesting that interactions between ceria and Pd have a negligible effect on the adsorption properties of CO. It does, however, affect the oxidation state of the palladium particles. For NO, there are differences between Pd/Al2O3 and Pd–Ce/Al2O3. On oxidized catalysts, Pd/Al2O3 is more efficient for NO dissociation. However, pre-reduction increases the amount of NO that can adsorb on Pd–Ce/Al2O3 and react to N2O and N2. In comparison with Pd/Al2O3, reduced Pd–Ce/Al2O3catalysts dissociate NO at relatively high temperatures but they are more reactive and favor N2 over N2O.