Probing Local Structures and Structural Dynamics in Solid Catalysts with Electrons

This requires a detailed, scale-bridging understanding of the structure of the entire catalyst system. However, a static structural understanding would be insufficient as catalysts are metastable compounds and undergo structural changes under catalytic working conditions. The extent of the changes depends on the local chemical potential. As such the local chemical potential influences the structures of the active sites and thus the catalytic performance. To complicate the problem, the structures of the active catalysts are often only stable under working conditions and in order to analyse them investigations under working conditions are required. In those experiments the structure and performance can be directly correlated in so called operando measurements.

In some cases, less than 1% of the accessible surface area are active and, thus, active sites are a very local concept for describing the functioning of a catalyst. Besides the local chemical potential, the working structures also depend on the real structure of the pristine material after synthesis, which cannot be detected by structural averaging techniques. To capture these local structural details, electron microscopy is the method of choice.

In this lecture I will motivate the importance of real structure investigation in heterogeneous catalysts as well as the scale-bridging use of operando electron microscopy focusing on thermal gas phase reactions. Furthermore, I will show the potential and possibilities in capturing the working structure of heterogeneous catalysts and discuss the limitations of the techniques for catalysis research.