Oxygen isotope equilibration and exchange as probes for differing dioxygeninteractions with pure and rhodia-promoted CeO2 and Al2O3

Comparisons are made between the catalytic activities of CeO2, Al2O3 and Rh 2O3 when pure, or in the case of CeO2 and Al2O3 when promoted by rhodia dis persed thereon, in respect of: (a) activity at 290 K for homomolecular oxyg en isotope equilibration of an equimolar (O-18(2) + O-16(2)) probe gas, the so-called R-0 process, (b) activity under T-ramp for heterophase oxygen is otope exchange between surface lattice O-16(s)2- and O-2 highly enriched in O-18, which is shown to occur predominantly by single-stay exchange of bot h oxygen atoms of dioxygen (the so-called R-2 process).