Design and development of solid-state nanostructures for catalysis

Catalytic processes are present in a wide range of aspects, from fundamental biological processes to modern chemical synthesis. In practical terms, catalysis has thrived as a rapidly growing industry. However, a significant gap in our understanding of catalytic processes exists between the molecular and industrial scales, arising from the complexity at the nano- and micro-levels of catalytic nanoparticles and their supports. Heterogeneous catalysts, where the catalyst is in a different phase than the reactants, are widely used due to their ease of retrieval from reaction mixtures. However, they typically require high temperatures and pressures to operate efficiently. Enhancing the efficiency of heterogeneous catalysts under milder conditions could have significant environmental and economic benefits.
In this thesis, a novel approach to designing and developing solid-state nanostructures for catalysis is presented. It encompasses three main components: the generation of catalytic nanoparticles, the fabrication of nanostructure supports, and post-processing techniques to enhance stability. Aerosol methods, specifically spark discharge generation, are employed to produce nanoparticles with high control over size, composition, and crystallinity. The fabrication of support structures, using epitaxial growth, resulted in close-packed tapered gallium phosphide nanowires and nano-trees that elevate catalytic nanoparticles, enhancing their accessibility to reactants during reactions. The thesis also addresses the challenge of stability for the catalytic nanoparticles in reaction environments, both for the use of planar supports and with high-aspect-ratio nanowire supports. The work includes the development of a method to study stability under reaction conditions, enabling the determination of suitable material sys-
tems. Finally, the catalytic evaluation of nanowire-supported palladium nanoparticles reveals promising results for the nanostructured catalysts, with a 15-fold increase in catalytic activity compared to using a planar support.