Studies of Molecular Interactions with Single Nanoparticles: Combining in Situ Plasmonic Nanospectroscopy with Transmission Electron Microscopy

Abstract: The cyclic methanol and hydrogen economies are two viable options in the strive for clean energy production. Industrial methanol synthesis is conducted over copper (Cu)-based catalysts. However, Cu is prone to oxidation, which leads to Cu catalyst deactivation. This highlights the need to probe catalyst performance and deactivation during relevant conditions, and why methods for operando catalyst monitoring are sought after. Moreover, individual catalyst particle-specific characteristics, such as grain boundaries, are likely to affect deactivation. Secondly, in view of the expanding hydrogen economy, efficient and reliable hydrogen sensors are required. To this end, the slowing response rate of palladium (Pd)-based hydrogen sensors over extended hydrogen sorption cycling is problematic. To enable studies of single particle-specific performance deterioration routes, I have in this thesis developed a correlative plasmonic nanospectroscopy and transmission electron microscopy approach for in situ studies of interactions between individual nanoparticles and molecules in the gas phase. As my main focus, I have applied the method to shed light on Cu nanoparticle oxidation, both in pure O2 and under CO oxidation reaction conditions. As a main result, I identified a distinct dependence of Cu oxidation on single particle-specific structural characteristics, such as grain boundaries. Furthermore, with in situ TEM imaging temperature-dependent competing oxidation mechanisms were observed and their corresponding single particle plasmonic signatures were mapped by electron energy-loss spectroscopy. As a second example, in hydrogen sorption cycling of polycrystalline Pd nanoparticles grain-growth was observed that slowed down sorption kinetics, whereby an explanation for the deterioration of Pd-based hydrogen sensors was identified.