We have examined the adsorption of CO, NO, and H2on modelPd/ceria catalysts, formed by vapor deposition of Pd metal ontoa flat, polycrystalline ceria support, using temperatureprogrammed desorption. For CO adsorption on freshly deposited Pdfilms, a substantial fraction of the CO reacts to CO2in TPD,between 450 and 550 K, indicating that oxygen from ceria can react with CO onPd. Prereduction of the catalyst by heating in CO or H2results inTPD curves which are virtually identical to that observed forPd/α-Al2O3(0001), suggesting that electronicinteractions between ceria and Pd have a negligible effect onthe adsorption properties. For NO, there are differences betweenPd/ceria and Pd/α-Al2O3(0001). Asignificantly higher fraction of the NO on Pd/ceria reactsto N2and N2O, and prereduction of thePd/ceria increases the amount of NO that can adsorb. Both ofthese results are interpreted as indicating that NO can adsorbon reduced ceria sites which are formed when lattice oxygen atthe Pd-ceria interface is transferred to the Pd. For H2, thedesorption curves are similar to that observed onPd/α-Al2O3(0001),except that the low-temperature feature assigned to the bulkhydride is less well resolved. If water is formed upon H2adsorption, it apparently readsorbs on the ceria. Theimplications of these results for reactions involving NO and COon Pd/ceria are discussed.
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Cordatos et al. (1996) studied this question.