LOW-TEMPERATURE ISOTOPIC OXYGEN EQUILIBRATION ON OXIDIZED PALLADIUM

A fast equilibration reaction 16O2 + 18O2 → 216O18O was found to proceed on partly oxidized palladium at, and below, room temperature when the oxide was made oxygen deficient. This was done by lowering the pretreatment pressure at 500-550° below the measured dissociation pressure of PdO. A highly reversible oxygen adsorption must be involved; it amounts to only 3 × 10-3 monolayer at 8 × 10-2 Torr and to an extrapolated value of about 1 × 10-2 monolayer at a few Torr, as revealed by pressure-temperature scans. The observed conditions for reactivity as well as the color changes observed on removing oxygen from the oxide lattice are very similar to those described in the literature for NiO where the origin of the reactivity has been difficult to prove conclusively.