Exploring thin flm and nanoparticle catalysis with magnetron sputtering in µ-reactors

This thesis explores the development, characterization, and application of catalytic systems for the conversion of carbon dioxide (CO₂) to methanol, a process critical to mitigating climate change through carbon-neutral energy cycles. Methanol, a versatile chemical feedstock and energy carrier, plays a key role in reducing greenhouse gas emissions, particularly when produced using renewable hydrogen and captured CO₂. However, challenges related to catalyst activity, selectivity, and long-term stability have yet to be optimized. This work addresses these challenges by employing a multidisciplinary approach that combines thin film deposition, advanced characterization techniques, and fundamental reaction studies.

A significant focus of this thesis is the use of magnetron sputtering to  synthesize δ-Ni₅Ga₃ thin films and nanoparticles, serving as model systems for CO₂ hydrogenation. The precise control offered by sputtering enables the deposition of well-defined catalytic materials with tailored phase compositions and surface morphologies. Detailed structural and chemical characterization of these catalysts is performed using a range of complementary techniques, including ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), ion scattering spectroscopy (ISS), grazing-incidence X-ray diffraction (GI-XRD), X-ray reflectometry (XRR), scanning electron microcopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The combination of these methods ofers valuable insights into the active sites and reaction mechanisms under operando conditions.

The research also investigates the stability of nanoparticle catalysts using AuTiO_x and CO oxidation as a model system. The work elucidates a strategy to enhance catalyst lifetime under high-temperature and oxidative conditions, providing a framework for designing more durable catalytic materials while preserving their catalytic activity. 

The core of the catalytic activity experiments in this thesis is represented by the µ-reactor system developed at DTU. These chips, characterized by an extremely low reaction volume of around 240 nL, allow for high-sensitivity measurements - detecting for minute quantities of products. 

From a broader perspective, this thesis highlights the significance of collaborative research in advancing catalysis, particularly through international partnerships and interdisciplinary approaches, such as the integration of methodologies from both chemistry and physics. By collaborating with global teams and leveraging cutting-edge facilities such as synchrotron radiation sources, we achieve a level of precision and scope that would be challenging to attain independently. This collaborative framework not only enhances our understanding of catalytic processes but also drives the development of innovative materials and methods, bridging the gap between fundamental science and industrial application.