Acceleration and controll of chemical reactions
Catalysis refers to the ability of certain substances, so-called catalysts, to influence the kinetics of a chemical reaction in a targeted manner. Catalysts reduce the activation energy of the respective chemical reaction without themselves being consumed. Catalytic processes take place at the outermost atomic layer of a catalyst. Therefore, it is not surprising that quantitative, surface-analytical methods such as Low Energy Ion Scattering (LEIS) or X-ray Photoelectron Spectroscopy (XPS, ESCA) are used both in catalyst development as well as in finding causes for catalyst deactivation.
LEIS investigation of the regeneration of a catalyst
One of the biggest challenges in the operation of catalysts is the elucidation of deactivation phenomena. The present example shows how the activity of a 3-way catalyst is adversely affected by "cold start" conditions. The catalyst consists of platinum and rhodium on an oxide support.
The LEIS spectrum of the surface of a new catalyst ("fresh") shows a clear platinum surface peak. If the catalyst is used under cold start conditions, this peak is no longer visible because the platinum surface is covered with soot. The platinum is therefore no longer available for a catalytic reaction. The soot can be removed by a regeneration step. This leads to an exposure of the platinum surface ("regenerated") and the catalytic activity is restored.