How Pt Interacts with CeO2 under the Reducing and Oxidizing Environments at Elevated Temperature: The Origin of Improved Thermal Stability of Pt/CeO2 Compared to CeO2

The interaction between Pt and CeO2 under reducing and oxidizing conditions as well as its effect on the thermal stability of Pt/CeO2 were extensively investigated by means of N-2, adsorption/desorption,Raman spectroscopy, CO chemisorption, H-2, TPR, XRD, and XPS techniques. In situ and ex situ Raman spectroscopy showed that Pt is anchored with the surface oxygen of CeO2 by forming Pt-O-Ce bond during the oxidative treatment of Pt/CeO2. Under the reducing condition, the static CO chemisorption presented that the amount of CO adsorbed on CeO2 is almost equal to that on Pt/CeO2, implying that Pt atom is located on the oxygen vacancy generated on reduced CeO2 surface. Strong Pt-O-Ce bond maintained the textural properties of Pt/CeO2 from oxidative treatment at temperature as high as 800 degrees C, as evidenced by the XRD patterns and BJH curves of the samples. Selective removal of the surface oxygen of Pt/CeO2, resulted in the decreased thermal stability of Pt/CeO2 due to the loss of Pt-O-Ce bond. Stronger interaction between Pt and CeO2 is observed when the oxidation temperature was increased from 500 to 800 degrees C, as evidenced by the shift of the surface reduction peak of Pt/CeO2, in H-2, TPR to the higher temperature. It is consistent with in situ Raman spectra of Pt/CeO2, which showed that Pt-O-Ce bond became more resistant to the reduction by H-2, after the oxidative treatment at 800 C. Hence, it is concluded that Pt-O-Ce bond plays an important role in improving the thermal stability of Pt/CeO2 upon the oxidative treatment at high temperature. Based on characterization results, the model is proposed to explain the interaction between Pt and CeO2 under the oxidative treatment.