| Popis: |
Most heterogeneous catalysis occurs on a collective of metal nanoparticles (NPs) in a size range of 3nm - 10nm. The strong coupling between NP size & shape - and catalytic activity proposed by model studies is impossible to reveal with state-of-the-art catalyst probing using flow reactors since these must be loaded with millions of diverse NP to have a sufficient turnover for mass-spectrometric detection. Therefore, the true nature of the emerging activity from a single NP will be hidden by ensemble smearing.We designed a prototype in the form of a Micro-Electro-Mechanical System (MEMS) device to drastically increase the sensitivity by several orders of magnitude compared to the current benchmark. The design is based on an electron transparent batch reactor sealed by a 2D material, which allows us to investigate catalyzed reactions under real conditions at the atomic scale with in-situ transmission electron microscopy (TEM), electron-energy-loss-spectroscopy (EELS) combined with atomic force microscopy (AFM). This design is expected to enable the spectral and structural characterization of ongoing chemical reactions over single metal nanoparticles to derive an activity-shape correlation. Through this research, we developed protocols for reliable pressure and gas composition measurements in AFM and EELS, which had not been reported in the literature to our knowledge. We constructed a setup to measure 2D membrane deflection with AFM in a pressure range of 0mbar to 2000mbar, allowing for reliable pressure testing of gas captured inside the reactor. Additionally, we developed a protocol to measure gas composition and leak rates out of the reactor with EELS at elevated temperatures, enabling the measurement of nitrogen leak rates out of reactors at temperatures up to 500 ◦C. Development of these protocols led to the discovery of a pattern to enhance the 2D material reactor seal. By treating sealed reactors at high temperatures and pressures, leak rates from hundreds of molecules per second could be significantly reduced to less than 1 molecule/s. We were also able to devise an approach for filtering and depositing single NPs into individual reactors. With further development, the devices and methods presented in this thesis can be used to raise the testing of catalysts to a new level of sensitivity. |
