Harmony and strength – a hybrid catalyst

Under the covers

Sharon Mitchell, from ETH Zurich, and Amalia Gallardo explain the concept behind the latest Green Chemistry cover.

Sharon: Gamma-valerolactone is a highly versatile chemical that is used to make a number of every day commodities such as vehicle fuels, pharmaceuticals and food ingredients. It is made from levulinic acid, which in turn can be obtained from the degradation of biomass.

To convert levulinic acid to gamma-valerolactone, we need the help of a catalyst. Catalysts are materials often based around a metal, which enable a reaction to occur more easily, for example by bringing the reacting components into close proximity and holding them in the correct orientation relative to each other.

Ruthenium is able to catalyse this reaction better than many other metals, but it is expensive due to its limited availability (it is approximately 2,000 times more expensive than iron). We have therefore been trying to develop more efficient catalysts based on ruthenium. We’ve done this by appending an organic (carbon-based) molecule, known as a ligand, to the metal.

We’ve shown by an in-depth analysis that the resulting hybrid catalyst has improved performance, due to the specific properties of the organic–metal interface.