Spectroscopic Investigations of Solid Catalysts
X-ray photoelectron spectroscopy (XPS) is used for the chemical characterization of surfaces. The method is based on the external photoelectric effect, in which photoelectrons are released from a solid by electromagnetic radiation. The kinetic energies of the photoelectrons are element-specific. Their measurement allows not only the qualitative and quantitative identification of elements, but also the determination of the chemical environment and the electronic structure of surface atoms. With the help of a combined heating/cooling unit in the analysis chamber itself, changes in sample surfaces can be observed spectroscopically in situ. A reaction cell is attached to the sample preparation chamber in which solid-gas reactions up to 900 °C can be performed. After the respective reaction the sample is brought into the analysis chamber without contact with the ambient atmosphere and spectroscopically examined.
The instrument is additionally equipped with a UV light source to generate photoelectrons in the sample surface. Ultraviolet photoelectron spectroscopy (UPS) analyzes the Density of States (DOS) of a compound and thus serves to determine the valence band structure of surfaces and adsorbates.
Raman spectroscopy is an excellent method to observe local structural changes of catalysts in heterogeneous catalysis. This includes structural changes during a crystallization process as well as structural changes during a catalytic reaction itself. The data can help to identify intermediates and products of a heterogeneously catalyzed reaction or to elucidate reaction mechanisms. In addition, defects in the local crystal structure can be observed, which makes Raman spectroscopy a valuable method for the investigation of nanomaterials. The spectrometer is equipped with two different sample environments that allow in situ spectroscopy of a solid during heating or cooling or during a gas phase reaction.