Iron instead of precious metal

Chemists don't like precious metals – at least not when they need the expensive materials as catalysts to accelerate reactions or guide them in a particular direction. And this is often the case, as in an important step in the production of polyethylene, a substance that makes plastic bags light, flexible and stable.

However, a team of scientists from the Max Planck Institute for Chemical Physics of Solids in Dresden and the Fritz Haber Institute of the Max Planck Society in Berlin have now developed a catalyst using iron and aluminium that works just as well as the conventional palladium catalyst, but costs much less. To identify the iron-aluminium alternative, the scientists first systematically ascertained what properties the material would need. They plan to use this same procedure to search for catalysts for other reactions in future.

Were it not for the fact that the chemical industry routinely uses palladium as a reagent for polyethylene, plastic bags would be a great nuisance, ripping when loaded with just a couple of apples and a carton of milk. However, we are spared this fate by the reliable work of the precious metal. Palladium converts ethine, more commonly known as acetylene, into ethene, also known as ethylene, which is used to make polyethylene. Ethylene always contains traces of acetylene, because both substances are obtained from crude oil and are not easily separated.

However, acetylene interferes in the conversion of ethylene to polyethylene. Thererfore, unless it is first converted to ethylene by the attachment of two hydrogen atoms in the presence of palladium, the resulting plastic is of poor quality.

Worldwide production of polyethylene amounts to 80 million tonnes each year, thus the costs of acetylene conversion add up to a considerable sum. However, these costs could drop significantly, as it may now be possible for industry to manage without the palladium catalyst, using an intermetallic compound of iron and aluminium instead.

Working with the Ludwig Maximilians Universität Munich and Forschungszentrum Jülich, scientists from Dresden's Max Planck Institute for Chemical Physics of Solids and the Fritz Haber Institute of the Max Planck Society in Berlin have identified this material as an effective substitute for palladium, finding that it hydrogenates acetylene to ethylene just as efficiently as precious-metal catalysts.