Activation of Oxygen in Ce2Zr2O7+x across Pyrochlore to Fluorite Structural Transformation: First-Principles Analysis

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• 作者：Asha Gupta ; Anil Kumar ; U. V. Waghmare ; M. S. Hegde
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：January 26, 2017
• 年：2017
• 卷：121
• 期：3
• 页码：1803-1808
• 全文大小：441K
• ISSN：1932-7455

文摘

Cationic substitution of zirconium in ceria (CeO₂) greatly improves its oxygen storage capacity (OSC) and thermal stability. Although the fluorite structure of Ce_0.5Zr_0.5O₂ (Ce₂Zr₂O₈) exhibits good oxygen storage and release properties, its reduced counterpart Ce₂Zr₂O₇ in the pyrochlore structure derived from the fluorite structure does not. Here, we present an analysis of the structural evolution of Ce₂Zr₂O_7+z from pyrochlore-Ce₂Zr₂O₇ (z = 0) to fluorite-Ce₂Zr₂O₈ (z = 1) using first-principles density functional theoretical calculations and bond-valence theory and correlate the consequent activation of oxygen to the observed oxygen storage capacity. The gradual addition of oxygen atoms to the otherwise ordered vacant tetrahedral sites for anions in pyrochlore-Ce₂Zr₂O₇ structure will lead to a transition to fluorite-Ce₂Zr₂O₈ structure, and we demonstrate that this transition involves an increase in the number of weakly bonded, activated oxygen sites that are pertinent to higher OSC observed for the fluorite-Ce_0.5Zr_0.5O₂ structure. The structural descriptors of OSC demonstrated here will facilitate the understanding and rational design of oxide materials with improved OSC, which is key to catalyzing a number of reactions for various applications.