PDRHO2 FORMATION DURING THE AIR OXIDATION OF A PD-15RH ALLOY

The surfaces of air-oxidized Pd-15Rh alloys have been examined by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The XPS results indicate that the near-surface region of samples oxidized in the temperature range 1075 to 1125 K contains Pd in both the plus 2 and plus 1 oxidation states and Rh in the plus 3 oxidation state. The ratio of Pd (I) to Rh (III) is 1:1. Raman spectra confirm that two Pd-containing phases, PdO and PdRhO//2, are present in the near-surface region and eliminate the possibility that Rh//2O//3 is present. A resonant Raman effect is observed in anhydrous PdO for exciting wavelengths in the vicinity of 500 nm.