Model catalysts

Catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. The effect of catalysts is known from very ancient times, but it is only about two hundred years, since we started to understand the phenomenon. Nowadays in Europe, catalytic reactions are associated with about 30% of gross domestic product and they are involved at some point in the processing of over 80% of all manufactured products.

Importance of the industrial catalysis can be illustrated by the Haber-Bosch process. Since its invention in the first decade of the 20^th century it has served as the main method of the production of ammonia, which is widely used in agriculture as a fertilizer. Thanks to this process alone, the global population was able to increase almost fivefold in the last century. As a side effect, nearly half of the nitrogen in an average human body finds its origins in the Haber-Bosch process.

However, industrial catalysis is complex! For instance, in heterogeneous catalysis a reaction between gaseous components proceeds at the surface of a solid material usually containing several components. The reaction comprises multiple steps, such as adsorption, dissociation and diffusion of reactants, diffusion and desorption of products and may even include a temporary changes of the catalyst. Each of the steps is a reaction on its own. Each step can have a different rate, it can happen on a different site on the surface and it can be affected by other reaction steps that happen at the same time on the surface. Understanding of the whole reaction requires the development of specific, surface sensitive techniques that have high spatial, temporal and chemical resolution and can operate during the ongoing reaction.

Currently, most methods of the surface science are not suitable for studies of real 3D industrial catalysts that usually operate at an elevated temperature and pressure. For this reason, simplified versions of the catalysts, i.e. model catalysts, are often studied at simplified environmental conditions. 3D porous multicomponent catalysts are usually studied as nanoscopic clusters supported by planar single-crystals and temperature and pressure are usually significantly lowered in order to allow functioning of the probing methods. Only lately, methods that are able to operate close to the operational conditions of the industrial catalysts, i.e. operando methods, are developed and utilized. Examples of such methods are near-ambient pressure scanning tunneling microscopy (NAP-STM) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS).

In order to develop cleaner and more effective catalysts of the future, we need to fully understand microscopic processes taking place on the surface and we need to connect these processes with macroscopic effects. Study and development of new model catalysts are therefore one of the cornerstones of the research in the Nanomaterials group.