Towards Atomic Scale Insight into Catalysis with Nanochannels and Microscopy

The chemical industry is a cornerstone of modern society but also a major contributor to global environmental challenges. Since most chemical production relies on heterogeneous catalysis, improving catalytic processes offers a pathway to reduce energy consumption and resource use. This thesis aims to advance the atomic-scale understanding of liquid-phase heterogeneous catalysis, focusing on metallic nanoparticles and their structural dynamics during reactions.

To enable such studies, transmission electron microscopy (TEM) was combined with nanochannel liquid cells developed by InsightChips. These chips were characterized in terms of liquid flow, membrane deformation under pressure, and mixing behaviour, with flow rates and diffusion coefficients quantified using fluorescence microscopy and liquid mixing capabilities studied using electron energy loss spectroscopy (EELS). Non-destructive methods for estimating channel thickness were developed, including a Fabry–Perot-based optical approach.

Beam effects in the TEM were systematically investigated, revealing that prolonged electron beam exposure transforms silicon nitride membranes into silicon oxide and induces radiolysis in the liquid phase, generating reactive species such as H₂O₂ and O₂ as well as a number of other radicals, ions and semi-stable molecules. These findings underscore the importance of dose control in liquid-phase TEM experiments.

Catalytic studies were initiated using platinum nanoparticles and hydrogen peroxide decomposition as a model system. EELS measurements confirmed catalytic activity, though limitations in flushing and time resolution hindered quantitative analysis. A plasmon-based approach using ascorbic acid oxidation was also explored, suggesting electron transfer processes at the nanoparticle surface.

Together, these studies demonstrate the feasibility of atomic-scale catalytic investigations in liquid environments and highlight key challenges in experimental control, imaging strategies, and chip design. The work lay a foundation for future in situ studies aimed at optimizing catalytic efficiency and reducing the environmental impact of chemical processes.