FRESH Lecture: "The active site in the spotlight!"
- Prof. dr. Moniek Tromp (HIMS, UvA)
- 9 February 2017
- Gorlaeus Building
2333 CC Leiden
Detailed information on the structural and electronic properties of a catalyst or material and how they change during reaction is required to understand their reaction mechanism and performance. Like x-rays in a hospital can be used to visualise the bone structure of skeleton in a body, x-rays can be used to visualise the structure and electronics of molecules and materials. High energy x-rays expose the detailed structure providing information on the type of atoms, their position and geometry. This so-called x-ray absorption spectroscopy (XAS) can be applied while the catalysts are working, providing insights in how reactants bind to the active centre.
XAS has mostly been used to obtain a structural picture whereas the electronic structure is often poorly understood. The major disadvantage of XAS is that it determines an average of all the different structures present, as such blurring the image and making it more difficult to interpret. New developments in XAS using new instrumentation and data acquisition methods, while selecting specific x-ray energies provide more detailed electronic information than has been feasible so far. The charges on and bonding between atoms can now be visualised and their distribution and orientation studied, ultimately creating a 3-dimensional electronic picture or movie of the material. Other new developments focus on the increase of time resolution possible with XAS, i.e. allowing one to follow reactions down to the sub-millisecond to pico-second time regime, and characterizing different parts of the molecules (ligand, metal, substrate etc).
These novel selective XAS techniques (theory and instrumentation) are currently being developed and applied to catalytic systems and materials (incl. batteries and fuel cells, art objects) and important insights in large scale industrial processes have already been obtained. In this lecture I will show you some of the concepts behind these novel X-ray techniques, and demonstrate their strengths in important processes (e.g. catalysis and batteries).