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

Abstract

The interaction between Pt and CeO 2 under reducing and oxidizing conditions as well as its effect on the thermal stability of Pt/CeO 2 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 CeO 2 by forming Pt–O–Ce bond during the oxidative treatment of Pt/CeO 2 . Under the reducing condition, the static CO chemisorption presented that the amount of CO adsorbed on CeO 2 is almost equal to that on Pt/CeO 2, implying that Pt atom is located on the oxygen vacancy generated on reduced CeO 2 surface. Strong Pt–O–Ce bond maintained the textural properties of Pt/CeO 2 from oxidative treatment at temperature as high as 800 °C, as evidenced by the XRD patterns and BJH curves of the samples. Selective removal of the surface oxygen of Pt/CeO 2 resulted in the decreased thermal stability of Pt/CeO 2 due to the loss of Pt–O–Ce bond. Stronger interaction between Pt and CeO 2 is observed when the oxidation temperature was increased from 500 to 800 °C, as evidenced by the shift of the surface reduction peak of Pt/CeO 2 in H 2 TPR to the higher temperature. It is consistent with in situ Raman spectra of Pt/CeO 2, 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/CeO 2 upon the oxidative treatment at high temperature. Based on characterization results, the model is proposed to explain the interaction between Pt and CeO 2 under the oxidative treatment.