Rasmus Svensson, Kemisk fysik

Heterogeneous catalysis is crucial in a range of environmental and industrial technologies, ranging from emission control and the utilization of greenhouse gases to the production of fuels and chemicals. Understanding and optimizing the catalytic performance is challenging, as industrial catalysts are generally ill-defined mixtures of metal and oxide phases. Moreover, the structures and chemical properties respond sensitively to the reaction environments.

Atomic scale understanding of catalytic reactions under relevant reaction conditions is beneficial to aid the discovery of catalyst materials. In this thesis, quantum mechanical calculations are combined with kinetic simulations to elucidate the synergy between different catalyst constituents and the effects of reaction environment on catalytic reactions. To investigate the metal/metal interplay and the influence of an aqueous reaction environment, the direct formation of H₂O₂ from H₂ and O₂ over water-solvated PdAu single-atom alloy nanoparticles is explored. The interplay between metal and oxide phases is studied in connection with CO₂ hydrogenation to methanol. The dynamic behavior of nanoparticles is probed using kinetic Monte Carlo simulations in inert and reactive atmospheres.

The formation of H₂O₂ relies on the facile desorption of protons from the surface to the water solution, leaving the electrons in the metal surface. Ab initio molecular dynamics simulations reveal that the metal/water interface affects the adsorption properties of H₂ and O₂ also on other metal surfaces. Similar synergetic effects occur between metal nanoparticles and oxide supports, where the adsorption of H₂ on oxides is stabilized close to metal nanoparticles, owing to an oxide-to-metal charge transfer. The metal/oxide synergy results in novel catalytic properties under reaction conditions, which is found to have important implications for the reaction intermediates in the case of CO₂ hydrogenation to methanol over Cu/ZnO catalysts.

The work highlights the interplay between the different phases in nano-sized catalyst materials. The synergy results in modified catalyst properties and new catalytic pathways under reaction conditions. Understanding of these processes at the atomic scale could potentially be used to optimize new materials in heterogeneous catalysis.