Universiteit Leiden

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Imaging complex model catalysts in action

From surface science towards industrial practice using high-pressure scanning tunneling microscopy.

Rik Mom
29 June 2017
Thesis in Leiden Repository

Finding a new catalyst is no easy task, especially since our understanding of catalysts at the atomic level is still lacking. In this thesis, a step is made to combine model catalysts that we do understand with realistic industrial conditions. This methodology comprises both the preparation of complex model catalysts and the development of new instrumentation. The model catalysts under study were MoO3 on Al2O3/NiAl(110), MoS2 on Au(111) and AuOx/WO3/ReO3 on Au(111). For MoO3, it is shown that the O2 pressure during physical vapor deposition preparation affects the particle dispersion, allowing for tuning of the structural properties of the model catalyst. For MoS2, the aim was to image the atomic structure of the active sites during the hydrodesulfurization reaction. To achieve this, an in-house developed high-pressure scanning tunneling microscope was modified to increase its corrosion resistance. Thus, it was possible to show that hydrocarbons can play a key role in determining the dominant active site structure of the MoS2 catalyst. Using the same microscope, gold oxide particles were imaged on Au(111). From our images and simple thermodynamic considerations, we determined that these particles are suprisingly stable. Finally, new methodology was developped to provide chemical contrast to high-pressure scanning tunneling microscopy.