Facilitating role of Pd for hydrogen, oxygen and water adsorption/desorption processes from bulk CeO2 and CeO2/gamma- Al2O3

The enhanced rates of reduction and re-oxidation of ceria in the presence of Pd, was investigated on both bulk ceria as well as ceria deposited over gamma-Al2O3. Pd addition and surface area enhancement by gamma-Al2O3 decreased the reduction temperature of CeO2 as monitored by temperature programmed reduction (TPR) in H-2. Temperature programmed oxidation (TPO) and temperature programmed thermal decomposition (TPtD) measurements revealed similar results of more favorable temperatures of oxidation and thermal decomposition. Pd assisted oxygen removal from CeO2 through a reverse spillover process as monitored by the temperature programmed thermal decomposition experiments was evident from the decomposition temperature of PdO to Pd. The adsorption microcalorimetry measurements at 323 K revealed that hydrogen adsorption initiated over Pd extends to CeO2 by migration (or spillover). Oxygen adsorption, however, was restricted to Pd surface at 323 K. Also at the same temperature, initial H2O adsorption was accompanied by very high heats at low coverages indicating surface oxidation. At higher pressures, H2O adsorption extended to coverages representative of the monolayer over.-Al2O3, the heats of adsorption measured at these high coverages corresponded to water condensation