Moragues Thomas, Agrachev Mikhail, Mitchell Sharon, Jeschke Gunnar, Pérez-Ramírez Javier, deMello Andrew J
Institute of Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1, Zürich, 8093, Switzerland.
Institute of Molecular Physical Science, Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1, Zürich, 8093, Switzerland.
Small Methods. 2025 Jul;9(7):e2401771. doi: 10.1002/smtd.202401771. Epub 2025 Jan 15.
In situ monitoring is essential for catalytic process design, offering real-time insights into active structures and reactive intermediates. Electron paramagnetic resonance (EPR) spectroscopy excels at probing geometric and electronic properties of paramagnetic species during reactions. Yet, state-of-the-art liquid-phase EPR methods, like flat cells, require custom resonators, consume large amounts of reagents, and are unsuited for tracking initial kinetics or use with solid catalysts. To overcome these limitations, a droplet-based microfluidics platform is introduced for real-time EPR monitoring of liquid-phase catalytic reactions. By encapsulating solid and dissolved species within nanoliter droplets, this approach enables precise control over mass transport, reduces reagent consumption, and maintains uniform residence times irrespective of acquisition duration, permitting precise analysis of each spectral component under identical conditions. The platform's compatibility with standard resonators facilitates straightforward integration into any EPR spectrometer. Its versatility is demonstrated by monitoring dynamic ligand exchange processes, key for activating homogeneous catalysts, and tracking redox and radical kinetics in ascorbic acid oxidation by Cu(II) catalysts. Importantly, this method captures both supported and dissolved transition metal species, offering comprehensive insights into catalyst deactivation via metal leaching. This microfluidic approach sets a new standard for liquid-phase in situ EPR measurements, advancing studies of homogeneous and heterogeneous catalytic systems.
原位监测对于催化过程设计至关重要，它能实时洞察活性结构和反应中间体。电子顺磁共振（EPR）光谱在探测反应过程中顺磁物种的几何和电子性质方面表现出色。然而，诸如平板池等先进的液相EPR方法需要定制谐振器，消耗大量试剂，且不适用于跟踪初始动力学或与固体催化剂一起使用。为克服这些限制，引入了一种基于液滴的微流控平台，用于液相催化反应的实时EPR监测。通过将固体和溶解的物种封装在纳升级液滴中，这种方法能够精确控制传质，减少试剂消耗，并且无论采集持续时间如何都能保持均匀的停留时间，从而允许在相同条件下对每个光谱成分进行精确分析。该平台与标准谐振器的兼容性便于直接集成到任何EPR光谱仪中。通过监测动态配体交换过程（这是激活均相催化剂的关键）以及跟踪铜（II）催化剂催化抗坏血酸氧化过程中的氧化还原和自由基动力学，证明了其多功能性。重要的是，这种方法能够捕获负载型和溶解态的过渡金属物种，为通过金属浸出导致的催化剂失活提供全面的见解。这种微流控方法为液相原位EPR测量设定了新的标准，推动了均相和非均相催化体系的研究。
