Nanocatalysts Unravel the Selective State of Ag,ChemCatChem

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Nanocatalysts Unravel the Selective State of Ag
ChemCatChem ( IF 3.8 ) Pub Date : 2020-04-01 , DOI: 10.1002/cctc.202000035
Maximilian Lamoth ₁ , Travis Jones ₁ , Milivoj Plodinec ₁ , Albert Machoke ₂ , Sabine Wrabetz ₁ , Michael Krämer ₃ , Andrey Karpov ₃ , Frank Rosowski _{3,

4} , Simone Piccinin ₅ , Robert Schlögl _{1,

2} , Elias Frei ₁

Affiliation

In the present work, we report on a comparative study of model catalysts during ethylene epoxidation reaction under industrially relevant conditions. The catalysts consist of Ag nanoparticles <6 nm and a reference sample ∼100 nm. Combining catalytic data with transmission electron microscopy, thermal desorption spectroscopy, and density functional theory allows us to show that catalytic performance is linked to the oxygen concentration in/on the Ag particles. Isotope experiments using ¹⁸O₂ and C¹⁸O₂ are conducted to gain insight into the nature and location of oxygen in/on the Ag nanoparticles. The oxygen species responsible for the CO₂ formation and inhibition of the overall catalytic activity are identified, and the abundance of those species is shown to depend strongly on the pre‐treatment and reaction conditions, showing both are critical for effective oxygen management. By comparison with a conventional Ag/α ‐Al₂O₃ catalyst, we demonstrate a low concentration of oxygen in/on Ag leads to the highest selectivity regardless of particle size. However, particle size dependent oxophilicity leads to significantly lower TOFs for the Ag nanoparticles. This study provides fundamental understanding of the performance of supported Ag particles in ethylene epoxidation and offers new strategies to improve performance under industrially relevant conditions.

中文翻译：

纳米催化剂揭示了银的选择性状态

在目前的工作中，我们报告了在工业相关条件下乙烯环氧化反应过程中模型催化剂的比较研究。催化剂由<6 nm的Ag纳米颗粒和〜100 nm的参考样品组成。将催化数据与透射电子显微镜，热脱附光谱法和密度泛函理论相结合，我们可以证明催化性能与Ag颗粒中/上的氧浓度有关。进行了使用¹⁸ O ₂和C ¹⁸ O _2的同位素实验，以了解Ag纳米颗粒中/上的氧的性质和位置。负责CO ₂的氧气种类确定了整体催化活性的形成和抑制，并且表明这些物种的丰度在很大程度上取决于预处理和反应条件，表明两者对于有效的氧气管理都是至关重要的。与传统的Ag / α- Al ₂ O ₃催化剂相比，我们证明了低浓度的Ag中/上的氧气会导致最高的选择性，而与颗粒大小无关。然而，粒度依赖性的亲氧性导致Ag纳米颗粒的TOF明显降低。这项研究提供了对负载的Ag颗粒在乙烯环氧化中的性能的基本了解，并提供了在工业相关条件下提高性能的新策略。

更新日期：2020-04-01

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