Experts find secret to gold’s catalytic powers

Scientists at the Cardiff Catalysis Institute reveal reason behind gold’s unparalleled catalytic ability

A team led by experts at Cardiff University have peered deep inside the structure of a gold catalyst to find the reason for the material’s remarkable activity.

The team, from the Cardiff Catalysis Institute, have discovered a cocktail of different sized gold particles within the catalyst that each contribute, to different degrees, to gold’s catalytic ability.

Publishing their findings in the journal Nature Communications, the researchers believe that this unique insight, a first of its kind, can be used to modify the production methods of gold catalysts in order to make them even more efficient at speeding up chemical reactions.

Professor Graham Hutchings, Director of the Cardiff Catalysis Institute, said: “Ever since we first discovered gold’s remarkable catalytic ability, we’ve been examining its detail right down to the nanoscale -- one-billionth of a metre -- to find out what gives it these unparalleled characteristics.”

The team, which also included researchers from Lehigh University and Tokyo Metropolitan University, have now shown that within the catalyst there exists a wide distribution of gold species: nanoparticles larger than one nanometre in size; sub-nanometre clusters containing less than 20 atoms; and individual gold atoms.

“We’ve conclusively shown that it is not the particles or the individual atoms or the clusters which are solely responsible for the efficient catalysis, but in fact a combination of all three which each contribute to different degrees,” continued Professor Hutchings.

The research showed that the sub-nanometre clusters were the most efficient way of using gold to catalyse reactions, whereas the larger particles were less efficient and the individual atoms even less

To arrive at their conclusions, the researchers examined gold on iron oxide samples under an extremely powerful electron microscope, and correlated their observations with the catalytic performance of the samples themselves. The results showed that the catalytic performance depended on how the samples were originally prepared, which causes changes in the gold distributions.

This study was supported by the Japanese Society for the Promotion of Science which supported Dr Simon Freakley, from the Cardiff Catalysis Institute, to travel to the lab of Professor Masatake Haruta, the discoverer of this catalyst system, to learn about the effect of preparing the catalysts by different methods.

Qian He, a research fellow at Cardiff University who led the electron microscope study, said: “In the end, there were subtle differences in the order and speed in which the ingredients were added while preparing the material. When examined under the electron microscope, it was clear that the two slightly different methods produced quite different distributions of particles, clusters and dispersed atoms on the support.”

Professor Hutchings and his team have pioneered research into gold catalysts in recent years, and made the landmark discovery that gold is a remarkable catalyst for the production of vinyl chloride – the main ingredient of PVC. They found that gold offers an alternative to the environmentally harmful and toxic mercury catalyst that was traditionally used in industry.

As a result of Professor Hutchings’ pioneering work, the gold catalyst has now been commercialised by leading chemicals company Johnson Matthey and is currently in production at a purpose built reactor in Shanghai, China.

Current estimates suggest that 20 million tonnes of vinyl chloride could be manufactured each year using the gold catalyst.