São Carlos Institute of Chemistry, University of São Paulo, P.O. Box 780, 13560-970 São Carlos, SP, Brazil.
J Chem Phys. 2018 Dec 28;149(24):244702. doi: 10.1063/1.5063732.
The adsorption of Zr on the CeO surfaces can lead to the formation of ZrO-like structures, which can play a crucial role in the catalytic properties of Ce Zr O as support for transition-metal catalysts; however, our atomistic understanding is far from satisfactory, and hence, it affects our capacity to engineer the combination of ZrO-CeO for catalysis applications. Here, we investigate the adsorption of Zr ( = 1 - 4) atoms on CeO(111) surfaces through density functional theory with the Hubbard model and bring new insights into the Zr-CeO interaction and the formation of ZrO-like structures on ceria. We found that the Zr atoms oxidize to Zr and strongly interact with the O anions, reducing the surface Ce cations to Ce (4 Ce atoms per Zr adatom), which stabilizes the system by more than 10 eV per Zr. As more Zr is adsorbed, the O species migrate from the sub-surface to interact with the on-surface Zr adatoms in hcp sites, producing a full ZrO-like monolayer, which contributes to reduce the strain induced by the increased size of the Ce cations compared with Ce. The simulated partial and full ZrO-like structure thicknesses agree with the experimental measurements. In addition, we found an unprecedented trend for the on-surface Zr atoms: our calculations show that they are less stable than Zr replacing Ce atoms from the first cation layer. Therefore, under sufficiently high temperatures, one expects the formation of a CeO-like/-ZrO/CeO structure, which may completely change the reactivity of the surface.
Zr 在 CeO 表面的吸附会导致形成类似 ZrO 的结构，这在 Ce-Zr-O 作为过渡金属催化剂载体的催化性能中起着至关重要的作用；然而，我们的原子水平理解还远远不够，因此，这影响了我们设计 ZrO-CeO 组合用于催化应用的能力。在这里，我们通过密度泛函理论与 Hubbard 模型研究了 Zr(=1-4)原子在 CeO(111)表面上的吸附，并对 Zr-CeO 相互作用以及 CeO 上形成类似 ZrO 的结构有了新的认识。我们发现 Zr 原子被氧化为 Zr，并与 O 阴离子强烈相互作用，将表面 Ce 阳离子还原为 Ce(每个 Zr 吸附原子有 4 个 Ce 原子)，这使体系稳定超过 10 eV/个 Zr。随着更多 Zr 的吸附，O 物种从亚表面迁移到与表面 hcp 位的 Zr 吸附原子相互作用，形成完整的 ZrO 类似单层，这有助于减少由于 Ce 阳离子尺寸增加而引起的应变。模拟的部分和完整 ZrO 类似结构的厚度与实验测量值一致。此外，我们还发现了表面 Zr 原子的一个前所未有的趋势：我们的计算表明，它们的稳定性不如从第一层阳离子层取代 Ce 原子的 Zr。因此，在足够高的温度下，预计会形成 CeO 类似/-ZrO/CeO 结构，这可能会完全改变表面的反应性。
