Herein we investigate the reaction intermediates formed during CO oxidation on copper-substituted ceria nanoparticles (Cu_0.1Ce_0.9O_2–x) by means of in situ spectroscopic techniques and identify an activity descriptor that rationalizes a trend with other metal substitutes (M_0.1Ce_0.9O_2–x, M = Mn, Fe, Co, Ni). In situ X-ray absorption spectroscopy (XAS) performed under catalytic conditions demonstrates that O^2– transfer occurs at dispersed copper centers, which are redox active during catalysis. In situ XAS reveals a dramatic reduction at the copper centers that is fully reversible under catalytic conditions, which rationalizes the high catalytic activity of Cu_0.1Ce_0.9O_2–x. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) show that CO can be oxidized to CO₃^2– in the absence of O₂. We find that CO₃^2– desorbs as CO₂ only under oxygen-rich conditions when the oxygen vacancy is filled by the dissociative adsorption of O₂. These data, along with kinetic analyses, lend support to a mechanism in which the breaking of copper–oxygen bonds is rate-determining under oxygen-rich conditions, while refilling the resulting oxygen vacancy is rate-determining under oxygen-lean conditions. On the basis of these observations and density functional calculations, we introduce the computed oxygen vacancy formation energy (E_vac) as an activity descriptor for substituted ceria materials and demonstrate that E_vac successfully rationalizes the trend in the activities of M_0.1Ce_0.9O_2–x catalysts that spans three orders of magnitude. The applicability of E_vac as a useful design descriptor is demonstrated by the catalytic performance of the ternary oxide Cu_0.1La_0.1Ce_0.8O_2–x, which has an apparent activation energy rivaling those of state-of-the-art Au/TiO₂ materials. Thus, we suggest that cost-effective catalysts for CO oxidation can be rationally designed by judicious choice of substituting metal through the computational screening of E_vac.

中文翻译：

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过渡金属取代的二氧化铈纳米粒子的原位光谱和机理研究

本文中，我们通过原位光谱技术研究了在CO氧化过程中在铜取代的二氧化铈纳米颗粒（Cu _0.1 Ce _0.9 O _{2– x}）上形成的反应中间体，并确定了与其他金属替代物（M _0.1 Ce _0.9 O _{2– x}，M = Mn，Fe，Co，Ni）。在催化条件下进行的原位X射线吸收光谱（XAS）表明，O ^2–转移发生在分散的铜中心，这些铜在催化过程中具有氧化还原活性。原位XAS分析表明，在催化条件下铜中心的还原是完全可逆的，这使Cu _0.1 Ce _0.9 O _{2– x}的高催化活性合理化。环境压力X射线光电子能谱法（AP-XPS）和原位漫反射红外线傅里叶变换光谱法（DRIFTS）表明，CO可被氧化成CO ₃ ^2-不存在的O- ₂。我们发现，CO ₃ ^2-脱附的CO ₂仅在富氧条件下，当氧空位是通过的O-解离吸附填充₂。这些数据以及动力学分析为以下机制提供了支持：在富氧条件下，决定铜-氧键的断裂速率是决定性的，而在贫氧条件下，重新填充所产生的氧空位则是决定速率的机理。基于这些观察和密度泛函计算，我们引入了计算出的氧空位形成能（E _vac）作为取代二氧化铈材料的活性描述子，并证明E _vac成功地使M _0.1 Ce _0.9 O ₂的活性趋势合理化。_{– x}跨越三个数量级的催化剂。E _vac的适用性三元氧化物Cu _0.1 La _0.1 Ce _0.8 O _{2– x}的催化性能证明了其为有用的设计描述符，该催化剂的表观活化能可与最新的Au / TiO ₂材料媲美。因此，我们建议可以通过E _vac的计算筛选，通过明智地选择取代金属来合理设计具有成本效益的CO氧化催化剂。