In Situ EPR Study of the Redox Properties of CuO–CeO2 Catalysts for Preferential CO Oxidation (PROX)

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• 作者：Feng Wang ; Robert Büchel ; Anton Savitsky ; Michal Zalibera ; Daniel Widmann ; Sotiris E. Pratsinis ; Wolfgang Lubitz ; Ferdi Schüth
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：June 3, 2016
• 年：2016
• 卷：6
• 期：6
• 页码：3520-3530
• 全文大小：596K
• 年卷期：0
• ISSN：2155-5435

文摘

Understanding the redox properties of metal oxide based catalysts is a major task in catalysis research. In situ electron paramagnetic resonance (EPR) spectroscopy is capable of monitoring the change of metal ion valences and formation of active sites during redox reactions, allowing for the identification of ongoing redox pathways. Here in situ EPR spectroscopy combined with online gas analysis, supported by ex situ X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), temporal analysis of product (TAP), and mass spectrometry (MS) studies, was utilized to study the redox behavior of CuO–CeO₂ catalysts under PROX conditions (preferential oxidation of carbon monoxide in hydrogen). Two redox mechanisms are revealed: (i) a synergetic mechanism that involves the redox pair Ce⁴⁺/Ce³⁺ during oxidation of Cu⁰/Cu⁺ species to Cu²⁺ and (ii) a direct mechanism that bypasses the redox pair Ce⁴⁺/Ce³⁺. In addition, EPR experiments with isotopically enriched ¹⁷O₂ established the synergetic mechanism as the major redox reaction pathway. The results emphasize the importance of the interactions between Cu and Ce atoms for catalyst performance. With the guidance of these results, an optimized CuO–CeO₂ catalyst could be designed. A rather wide temperature operation window of 11 K (from 377 to 388 K), with 99% conversion efficiency and 99% selectivity, was achieved for the preferential oxidation of CO in a H₂ feed.