Revealing the Size-Dependent d–d Excitations of Cobalt Nanoparticles Using Soft X-ray Spectroscopy

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• 作者：Zhangzhang Cui ; Chenlu Xie ; Xuefei Feng ; Nigel BecknellPeidong Yang ; Yalin Lu ; Xiaofang Zhai ; Xiaosong Liu ; Wanli Yang ; Yi-De Chuang ; Jinghua Guo
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2017
• 出版时间：January 19, 2017
• 年：2017
• 卷：8
• 期：2
• 页码：319-325
• 全文大小：558K
• ISSN：1948-7185

文摘

Cobalt-based catalysts are widely used to produce liquid fuels through the Fischer–Tropsch (FT) reaction. However, the cobalt nanocatalysts can exhibit intriguing size-dependent activity whose origin remains heavily debated. To shed light on this issue, the electronic structures of cobalt nanoparticles with size ranging from 4 to 10 nm are studied using soft X-ray absorption (XAS) and resonant inelastic X-ray scattering (RIXS) spectroscopies. The RIXS measurements reveal the significant size-dependent d–d excitations, from which we determine that the crystal-field splitting energy 10Dq changes from 0.6 to 0.9 eV when the particle size is reduced from 10 to 4 nm. The finding that larger Co nanoparticles have smaller 10Dq value is further confirmed by the Co L-edge RIXS simulations with atomic multiplet code. Our RIXS results demonstrate a stronger Co–O bond in smaller Co nanoparticles, which brings in further insight into their size-dependent catalytic performance.