de Souza Caldas Lucas, Prieto Mauricio J, Tănase Liviu C, Tiwari Aarti, Schmidt Thomas, Roldan Cuenya Beatriz
Department of Interface Science, Fritz-Haber Institute of the Max-Planck Society, Berlin 14195, Germany.
ACS Nano. 2024 May 28;18(21):13714-13725. doi: 10.1021/acsnano.4c01460. Epub 2024 May 13.
The activity, selectivity, and lifetime of nanocatalysts critically depend on parameters such as their morphology, support, chemical composition, and oxidation state. Thus, correlating these parameters with their final catalytic properties is essential. However, heterogeneity across nanoparticles (NPs) is generally expected. Moreover, their nature can also change during catalytic reactions. Therefore, investigating these catalysts at the single-particle level provides insights into how these tunable parameters affect their efficiency. To unravel this question, we applied spectro-microscopy to investigate the thermal reduction of SiO-supported copper oxide NPs in ultrahigh vacuum. Copper was selected since its oxidation state and morphological transformations strongly impact the product selectivity of many catalytic reactions. Here, the evolution of the NPs' chemical state was monitored during annealing and correlated with their morphology . A reaction front was observed during the reduction of CuO to CuO. From the temperature dependence of this front, the activation energy was extracted. Two parameters were found to strongly influence the NP reduction: the initial nanoparticle size and the chemical state of the SiO substrate. The CuO reduction was found to be completed first on smaller NPs and was also favored over partially reduced SiO regions that resulted from X-ray beam irradiation. This methodology with single-particle level spectro-microscopy resolution provides a way of isolating the influence of diverse morphologic, electronic, and chemical influences on a chemical reaction. The knowledge gained is crucial for the future design of more complex multimetallic catalytic systems.
纳米催化剂的活性、选择性和寿命严重依赖于诸如其形态、载体、化学成分和氧化态等参数。因此,将这些参数与其最终催化性能相关联至关重要。然而,纳米颗粒(NPs)之间的异质性通常是预期的。此外,它们的性质在催化反应过程中也会发生变化。因此,在单颗粒水平上研究这些催化剂能够深入了解这些可调参数如何影响其效率。为了解决这个问题,我们应用光谱显微镜研究了超高真空中SiO负载的氧化铜纳米颗粒的热还原过程。选择铜是因为其氧化态和形态转变对许多催化反应的产物选择性有强烈影响。在这里,在退火过程中监测了纳米颗粒化学状态的演变,并将其与形态相关联。在将CuO还原为CuO的过程中观察到了一个反应前沿。从这个前沿的温度依赖性中提取了活化能。发现有两个参数对纳米颗粒的还原有强烈影响:初始纳米颗粒尺寸和SiO衬底的化学状态。发现CuO的还原首先在较小的纳米颗粒上完成,并且也比由X射线束辐照导致的部分还原的SiO区域更有利。这种具有单颗粒水平光谱显微镜分辨率的方法提供了一种分离各种形态、电子和化学影响对化学反应的影响的方法。所获得的知识对于未来设计更复杂的多金属催化系统至关重要。