Thermal ageing of Pt on low-surface-area CeO₂–ZrO₂–La₂O₃ mixed oxides: Effect on the OSC performance

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• 作者：Jun Fan ; Xiaodong Wu ; Xiaodi Wu ; Qing Liang ; Rui Ran ; Duan Weng
• 关键词：Pt ; CeO₂&#x2013 ; ZrO₂&#x2013 ; La₂O₃ mixed oxides ; Ageing ; Encapsulation ; OSC
• 刊名：Applied Catalysis B ; Environmental
• 出版年：2008
• 期刊代码：4_09263373
• 类别：ce
• 出版时间：30 May 2008
• 卷：81
• 期：1-2
• 页码：38-48
• 文件大小：1021 K

摘要

This work aims at exploring the thermal ageing mechanism of Pt on ceria-based mixed oxides and the corresponding effect on the oxygen storage capacity (OSC) performance of the support material. Pt was supported on low-surface-area CeO₂–ZrO₂–La₂O₃ mixed oxides (CK) by impregnation method and subsequently calcined in static air at 500, 700 and 900 °C, respectively. The evolutions of textural, microstructural and redox properties of catalysts after the thermal treatments were identified by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and high-resolution transmission electron microscope (HRTEM). The results reveal that, besides the sintering of Pt, encapsulation of metal by the mixed oxides occurs at the calcination temperature of 700 °C and above. The burial of Pt crystallites by support particles is proposed as a potential mechanism for the encapsulation. Further, the HRTEM images show that the distortion of the mixed oxides lattice and other crystal defects are distributed at the metal/oxides interface, probably indicating the interdiffusion/interaction between the metal and mixed oxide. In this way, encapsulation of Pt is capable to promote the formation of Ce³⁺ or oxygen vacancy on the surface and in the bulk of support. The OSC results show that the reducibility and oxygen release behavior of catalysts are related to both the metal dispersion and metal/oxides interface, and the latter seems to be more crucial for those supported on low-surface-area mixed oxides. Judging by the dynamic oxygen storage capacity (DOSC), oxygen storage capacity complete (OSCC) and oxygen releasing rate, the catalyst calcined at 700 °C shows the best OSC performance. This evident promotion of OSC performance is believed to benefit from the partial encapsulation of Pt species, which leads to the increment of Ce³⁺ or oxygen vacancies both on the surface and in the bulk of oxides despite a loss of chemisorption sites on the surface of metal particles.