In these last years large research efforts have been devoted to the synthesis and investigation of reducible metal oxide surfaces modified with metal atoms and nanoparticles for improving their performance in a number of advanced applications. Among reducible metal oxides, iron oxides have the advantage to be made up from two of the most common elements on Earth. In this paper we analyze the structural, electronic, and magnetic consequences of the insertion of isolated noble metal atoms (Cu, Ag, Au) on the γ-Fe2O3 (001) surface. We have considered many different configurations for the single atoms: adsorbed, substitutional to iron atoms, or to oxygen atoms, and, using first principles calculations, we have studied how the presence of the noble metal atoms on the surface influences the surface stability, its reducibility, and, therefore, its catalytic activity, and how these properties depend on the kind of noble metal atom and its position. Our results show that noble metal atoms adsorbed on the surface facilitate the adsorption of CO molecules, and, among them, Cu atoms are those that bind best to the surface also providing the strongest adsorption energy for the CO molecule. At ambient temperature and pressure the noble metal atoms prefer to substitute the iron atoms than to just adsorb on the surface, but for Ag atoms the adsorption and substitutional energies are very close. The surfaces with Ag in place of Fe are the most reducible and reactive for exchange of oxygen atoms. Finally, Au is the best noble metal for oxygen substitution. Our results provide useful insights for the researchers designing and synthesizing new noble metal - iron oxides nanostructures for applications in biology, medicine, catalysis, and chemical analysis.

中文翻译：

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γ-Fe2O3 磁赤铁矿 (001) 表面贵金属改性引起的表面还原性、反应性和稳定性

在过去几年中，大量研究工作致力于合成和研究用金属原子和纳米粒子改性的可还原金属氧化物表面，以提高它们在许多高级应用中的性能。在可还原的金属氧化物中，氧化铁具有由地球上最常见的两种元素组成的优势。在本文中，我们分析了在 γ-Fe2O3 (001) 表面上插入孤立的贵金属原子（Cu、Ag、Au）的结构、电子和磁性后果。我们已经考虑了单个原子的许多不同配置：吸附、取代铁原子或氧原子，并且使用第一性原理计算，我们研究了表面上贵金属原子的存在如何影响表面稳定性，其可还原性，因此，其催化活性，以及​​这些特性如何取决于贵金属原子的种类及其位置。我们的结果表明，吸附在表面的贵金属原子促进了 CO 分子的吸附，其中，Cu 原子与表面结合最好，也为 CO 分子提供了最强的吸附能。在环境温度和压力下，贵金属原子更喜欢取代铁原子而不是仅仅吸附在表面上，但对于 Ag 原子，吸附能和取代能非常接近。用 Ag 代替 Fe 的表面对于氧原子的交换最易还原和反应。最后，Au 是最好的氧取代贵金属。