Gold clusters: gentle bond breakers
Methane is currently the prime chemical feedstock for larger carbohydrates. The current industrial standard to produce these is to thermally crack methane into smaller molecules and then use these in a mixture called synthesis gas of CO, CO2 and H2 to produce the larger carbohydrates, again using plenty of energy. This energy consumption could easily be reduced if a direct chemical reaction from methane (CH4) to, for instance, ethane (C2H6) would be possible. Such a reaction requires a catalyst, which unfortunately has not yet been found.
Researchers from the FELIX laboratory have, in close collaboration with partners from Ulm, Germany and Atlanta, US now found that tiny gold particles possess an important prerequisite for such a catalyst: in linking to the methane molecule, they selectively break one single C-H bond.
Catalysts prepare the molecules that need to be chemically transformed into another by weakening certain bonds so that less energy is required for the reaction to succeed. On the other hand, they should not weaken too many bonds at the same time such that the original molecule is modified too much, or even completely destroyed. The working of a catalyst is generally dictated by this fine balance.
Although gold in bulk form reacts very poorly with other substances (the reason why a golden ring never needs polishing) it can become chemically very active when it is reduced to a few-nanometer sized particle, or smaller. Using spectroscopic identification with the FELIX free electron lasers, it was demonstrated that methane molecules, when reacting with gold clusters, form a methyl (CH3) product. For this only one C-H bond of the methane needed to be broken.
The electronic structure of the gold particles is favorable for this process, enabling a “gentle” breaking of bonds. The results of this research will be helpful in guiding the rational design of novel catalytic materials.
"Selective C−H Bond Cleavage in Methane by Small Gold Clusters", Lang, S. M.; Bernhardt, T. M.; Chernyy, V.; Bakker, J. M.; Barnett, R. N.; & Landman, U.; Angew. Chem. Int. Ed.
Dr. J.M. Bakker, Radboud University, firstname.lastname@example.org