Gold on carbon is a classic pairing in chemistry. Such materials speed up important reactions, like producing vinyl chloride for plastics. But until now, no one had seen in detail how gold atoms behave on a graphite surface when the whole thing is immersed in a liquid.

The scientists built special capsules from graphene — a sheet of carbon one atom thick. Inside, they poured organic liquids — acetone and cyclohexanone. Then, using an electron microscope with atomic resolution, they tracked the motion of more than a million gold atoms. It turned out that the atoms don't stay put: they slide across the surface, meet, form pairs, and small clusters. Moreover, their behavior is influenced not only by the graphite surface itself but also by the liquid surrounding them. Acetone makes the atoms move differently than cyclohexanone.

These observations helped explain the difference in activity of gold-based catalysts in the reaction producing vinyl chloride — an important feedstock for plastics. Now, knowing how gold atoms come together and how the solvent affects them, we can purposefully create catalysts with desired properties. This is a step toward rational design of materials for chemistry, energy, and water purification.