Mechanochemistry as a tool for catalyst synthesis and catalysis

Mechanochemistry is a topic of high current interest and has been used for the synthesis of many different materials. Especially if done in ball mills, it is an excellent method for applications in catalysis, both in the synthesis of catalytic materials and in the catalytic reaction itself.

Ball milling approaches can be used for the synthesis of supported catalysts in a very simple manner by just mixing support and macroscopic metal powder, followed by milling. This does not only result in the formation of nanometer sized metal particles on the support, but also unusual alloys, which are hardly accessible by other methods, can be prepared. Ball milling can also lead to the conversion between polymorphs, and one of the most striking examples is the synthesis of corundum with very high surface area by the mechanochemically driven dehydrative phase transformation of boehmite, which, incidentally, can also be used to synthesize rare materials in the aluminum-oxygen-hydrogen system. The -alumina thus produced is highly stable and is useful in different catalytic transformations.

Also catalytic reactions themselves can be driven by ball milling. This has been shown for a number of different reactions, such as CO-oxidation, preferential CO-oxidation in hydrogen, depolymerization of different polymers, or the chlorination of methane. The most spectacular examples for a catalytic reaction in a ball mill is the continuous synthesis of ammonia from the elements at atmospheric pressure and room temperature over an iron catalyst modified by metallic cesium.

The presentation will give an overview over different aspects of mechanochemistry in catalysis and also touch the issue of scaling up milling processes.