PhD defense: Studies of Catalytic Materials with In Situ Transmission Electron Microscopy

This thesis explores the use of new, advanced electron microscopy techniques to study dynamic processes occurring in nanomaterials. The focus of this research is on the use of in situ liquid phase transmission electron microscopy (LP-TEM) to study the behavior of heterogeneous catalysts and related nanomaterials in a liquid phase at the nanometer scale. It was clear that the main challenge for successfully studying these materials in LP-TEM is the effect of the electron beam interacting with the liquid and solid, causing degradation of several important oxides, such as SiO2, Al2O3 and MgO.

Possible strategies to mitigate this were found and include the use of lower electron dose rates, the use of more stable oxides (TiO2, ZrO2 and Nb2O5 in this work) and in the case of SiO2, the use of radical scavengers to lower the concentration of reducing radicals the oxide is exposed to. Using such a strategy, gold nanoparticles anchored on a TiO2 support was used as a model catalyst. This catalyst was successfully used to study the growth of the gold nanoparticles in water (specifically Ostwald ripening). It was also used to study the structural changes of this catalyst relevant for the selective oxidation of HMF, which was predominantly the result of gold nanoparticles detaching from the surface.

Through the use of LP-TEM combined with laboratory experiments, novel insights in both of these processes was obtained. In addition, this work also provides new strategies and clues for other studies on synthesis and evolution of solid heterogeneous catalysts in liquid phase.