Structures and Catalytic Properties of Cr–Cu Embedded CeO2 Surfaces with Different Cr/Cu Ratios

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• 作者：Hiroshi Yoshida ; Yuri Okabe ; Satoshi Misumi ; Haruka Oyama ; Kaori Tokusada ; Satoshi Hinokuma ; Masato Machida
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：December 1, 2016
• 年：2016
• 卷：120
• 期：47
• 页码：26852-26863
• 全文大小：877K
• ISSN：1932-7455

文摘

The effects of the Cr/Cu ratios of Cr–Cu-embedded CeO₂ surfaces (0.065 wt % Cu loading) on their local structures and catalytic activities were studied using experimental and theoretical approaches. The sample with a weight ratio of Cr/Cu = 1, which was prepared by wet impregnation followed by subsequent thermal aging at 900 °C for 25 h, showed catalytic activity higher than that of the Cu/CeO₂ sample in both CO–O₂ and CO–NO reactions. The activity of the catalyst was enhanced by increasing the Cr/Cu ratio. The highest activity occurred for a Cr/Cu ratio of around 3, and after it had been thermally aged, its activity was superior to that of Rh/CeO₂. Having more Cr than Cu increases the surface concentration of the Cu⁺ sites, which promotes CO adsorption and its reaction with surface O atoms. As-formed surface O vacancies are filled by the dissociative adsorption of O₂ and/or NO. At the optimum composition, almost all of the Ce sites on the outermost layer are replaced by Cr and Cu, and oxidative chemisorption of CO and NO as carbonate and nitrate/nitrite, respectively, on the CeO₂ surface becomes difficult. This situation enables more efficient dissociation of adsorbed NO and faster desorption of CO₂, thereby leading to higher catalytic activity. Isocyanate species (NCO) that form on the Cu⁺ sites are a possible reaction intermediate for the CO–NO reaction.