Eveline Bus

An in situ and operando X-ray absorption spectroscopy setup for measuring sub-monolayer model and powder catalysts.

A new spectroscopic cell has been designed for studying model catalysts using in situ or operando X-ray absorption spectroscopy. The setup allows gas treatment and can be used between 100 and 870 K. Pressures from 10(-3) Pa up to 300 kPa can be applied. Measurements on model systems in this particular pressure range are a valuable extension of the commonly used UHV characterization techniques. Using this setup, we were able to analyze the Au L3 EXAFS of a silica wafer covered with sub-monolayer concentrations of gold (0.05 ML). By modifying the sample holder, powder catalysts can also be analyzed under plug-flow conditions. As an example, the reduction of a Au/SiO2 powder catalyst prepared from HAuCl4 was followed.

Structure of Catalytically Active Sites in Supported Metal Catalysts

The adsorption site and the mode of ethylene bonding on Pt/Al2O3 catalysts have been determined. Theoretically obtained signatures using FEFF8 showed that the possible bonding modes of ethylene can be distinguished, which is experimentally shown for the room temperature adsorption of ethylene. This study shows that it is feasible to determine the structures of the adsorption sites and the modes of bonding of hydrocarbon molecules on the surfaces of supported metal catalysts.