Pronounced Size Dependence in Structure and Morphology of Gas-Phase Produced, Partially Oxidized Cobalt Nanoparticles under Catalytic Reaction Conditions

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• 作者：Stephan Bartling ; Chunrong Yin ; Ingo Barke ; Kevin Oldenburg ; Hannes Hartmann ; Viola von Oeynhausen ; Marga-Martina Pohl ; Kelly Houben ; Eric C. Tyo ; S枚nke Seifert ; Peter Lievens ; Karl-Heinz Meiwes-Broer ; Stefan Vajda
• 刊名：ACS Nano
• 出版年：2015
• 出版时间：June 23, 2015
• 年：2015
• 卷：9
• 期：6
• 页码：5984-5998
• 全文大小：9339K
• ISSN：1936-086X

文摘

It is generally accepted that optimal particle sizes are key for efficient nanocatalysis. Much less attention is paid to the role of morphology and atomic arrangement during catalytic reactions. Here, we unravel the structural, stoichiometric, and morphological evolution of gas-phase produced and partially oxidized cobalt nanoparticles in a broad size range. Particles with diameters between 1.4 and 22 nm generated in cluster sources are size selected and deposited on amorphous alumina (Al₂O₃) and ultrananocrystalline diamond (UNCD) films. A combination of different techniques is employed to monitor particle properties at the stages of production, exposure to ambient conditions, and catalytic reaction, in this case, the oxidative dehydrogenation of cyclohexane at elevated temperatures. A pronounced size dependence is found, naturally classifying the particles into three size regimes. While small and intermediate clusters essentially retain their compact morphology, large particles transform into hollow spheres due to the nanoscale Kirkendall effect. Depending on the substrate, an isotropic (Al₂O₃) or anisotropic (UNCD) Kirkendall effect is observed. The latter results in dramatic lateral size changes. Our results shed light on the interplay between chemical reactions and the catalyst鈥檚 structure and provide an approach to tailor the cobalt oxide phase composition required for specific catalytic schemes.