Nat. Commun. 7, 13057 (2016)

Methanol is a versatile fuel and energy vector that can be used directly in fuel cells, blended with transportation fuels or deployed as a hydrogen carrier. Its synthesis from syngas (a mixture of CO and H2) over copper–zinc catalysts is well-known, but there is debate about whether the surface-specific activity (turnover frequency, TOF) of copper nanoparticles is affected by particle size. Petra de Jongh, Krijn de Jong and colleagues in the Netherlands and Denmark now demonstrate that the TOF decreases significantly for particles below a certain size, suggesting that the reaction is indeed structurally sensitive.

The researchers synthesize 42 catalysts with a range of copper particle sizes (2–15 nm) and varying loadings of zinc. Since previous studies have suggested that chemisorption techniques to measure the copper surface area are affected by preconditions and catalyst structure, the researchers instead use X-ray diffraction and microscopy to characterize the particle size distributions. Under industrially-relevant conditions, they find that decreasing the size of the particles from 8 nm to 2 nm results in a decrease in TOF by a factor of 3, whether or not the catalyst contains zinc. They propose that this could be due to changes in the fraction of specific step sites or the higher number of low-coordinated copper atoms at small particle sizes, which are more easily poisoned by reaction intermediates.