Synthesis and characterization of catalysts: from single atoms to single nanoparticles

The increasingly severe effects of global warming call for improved technologies for storage and conversion of renewable power. Catalysts play a crucial part in achieving that goal. This thesis investigates model systems of catalysts with the aim of establishing a better fundamental understanding of their catalytic properties. Over the course of the PhD project, systems of mass selected single atoms and nanoparticles were synthesized and characterized. 

A literature study of dual- and triple-atom catalysts underlined the need for more controlled model systems to test new potential few-atom catalysts. Pd₁ and Pt₁ particles on both gold and carbon supports were tested for the electrochemical CO and CO₂ reduction reaction. In all cases, the tested single-atom catalysts showed no catalytic activity of interest, but many promising catalysts remain to be tested.

Different Pt nanoparticles were synthesized for electron microscopy analysis. A Pt nanoparticle imaged in a CO atmosphere and a single isolated Pt nanoparticle in a SiO₂ nano-cavity were achieved. Both of these nanoparticle systems provide a solid foundation for further investigation of the catalytic properties of single nanoparticles.

Additionally, a stepped Co single crystal was studied with STM. The Co crystal surface was shown to have different phases of local density of states. This insight could help shed light on the spin-quenching effect of adatoms on Co which would be relevant for catalytic ammonia production.