Affinity order among noble metals and CeO2

The affinity order among four kinds of major noble metals (Ru, Rh, Pd, and Pt) and CeO2 was investigated by XRD and XAFS techniques. The states of noble metals supported on CeO2 and the sintering behavior of CeO2 on calcination differed depending upon the kinds of noble metals. Rh and Pd retained their RhOCe and PdOCe bonds even after calcination at 800 °C, and Pt kept its PtOCe bond at 500 °C, while Ru on CeO2 formed bulk RuO2 on calcination at temperatures as low as 500 °C. Rh effectively prevented sintering of CeO2. The order of the affinity of the noble metals toward CeO2 was assumed to be Rh > Pd > Pt > Ru.