Tyndall National Institute, University College Cork, Lee Maltings, Prospect Row, Cork, Ireland.
J Chem Phys. 2012 Apr 7;136(13):134703. doi: 10.1063/1.3697485.
The modification of cerium dioxide with nanoscale metal clusters is intensely researched for catalysis applications, with gold, silver, and copper having been particularly well studied. The interaction of the metal cluster with ceria is driven principally by a localised interaction between a small number of metal atoms (as small as one) and the surface and understanding the fundamentals of the interaction of metal atoms with ceria surfaces is therefore of great interest. Much attention has been focused on the interaction of metals with the (111) surface of ceria, since this is the most stable surface and can be grown as films, which are probed experimentally. However, nanostructures exposing other surfaces such as (110) show high activity for reactions including CO oxidation and require further study; these nanostructures could be modified by deposition of metal atoms or small clusters, but there is no information to date on the atomic level details of metal-ceria interactions involving the (110) surface. This paper presents the results of density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U) calculations of the adsorption of a number of different metal atoms at an extended ceria (110) surface; the metals are Au, Ag, Cu, Al, Ga, In, La, Ce, V, Cr, and Fe. Upon adsorption all metals are oxidised, transferring electron(s) to the surface, resulting in localised surface distortions. The precise details depend on the identity of the metal atom. Au, Ag, Cu each transfer one electron to the surface, reducing one Ce ion to Ce(3+), while of the trivalent metals, Al and La are fully oxidised, but Ga and In are only partially oxidised. Ce and the transition metals are also partially oxidised, with the number of reduced Ce ions possible in this surface no more than three per adsorbed metal atom. The predicted oxidation states of the adsorbed metal atoms should be testable in experiments on ceria nanostructures modified with metal atoms.
纳米尺度金属簇对二氧化铈的修饰在催化应用中受到了广泛的研究，其中金、银和铜的研究尤其深入。金属簇与二氧化铈的相互作用主要是由少量金属原子（少至一个）与表面的局部相互作用驱动的，因此了解金属原子与二氧化铈表面相互作用的基本原理是非常重要的。人们非常关注金属与二氧化铈（111）表面的相互作用，因为这是最稳定的表面，可以作为薄膜生长，并且可以进行实验探测。然而，暴露在其他表面（如（110））上的纳米结构对于包括 CO 氧化在内的反应具有很高的活性，需要进一步研究；这些纳米结构可以通过金属原子或小簇的沉积来修饰，但迄今为止，关于涉及（110）表面的金属-二氧化铈相互作用的原子级细节，还没有任何信息。本文介绍了用密度泛函理论（DFT）修正后的（DFT+U）计算结果，该计算研究了在扩展的二氧化铈（110）表面上吸附了一些不同金属原子的情况；这些金属包括 Au、Ag、Cu、Al、Ga、In、La、Ce、V、Cr 和 Fe。在吸附过程中，所有金属都被氧化，向表面转移电子，导致局部表面变形。具体细节取决于金属原子的身份。Au、Ag 和 Cu 各自向表面转移一个电子，将一个 Ce 离子还原为 Ce(3+)，而在三价金属中，Al 和 La 被完全氧化，但 Ga 和 In 只是部分氧化。Ce 和过渡金属也被部分氧化，在这种表面上，每个吸附的金属原子最多可能有三个 Ce 离子被还原。吸附金属原子的预测氧化态应该可以在经过金属原子修饰的二氧化铈纳米结构的实验中进行测试。
