Gold isn’t inert, it just has bodyguards protecting it

Generally speaking, a catalyst is a material that enables a reaction without being consumed by it (some catalysts are consumed, but let’s not sweat the details). Every reaction needs to overcome an energy barrier to start—we heat stuff up to set it on fire, for instance. A catalyst reduces that barrier, allowing a reaction to start at much lower energies. Biological systems are incredibly good at making reactions run at low temperature and pressure through the use of catalysts. Industrial chemistry achieves speed, scale, and cost savings due to catalysts, enabling the production of everything from petrochemicals to drugs. To confirm this, the researchers studied the behavior of an oxygen molecule on each type of gold surface. They asked how much molecular oxygen would stick to the surface, and for the molecules that did stick, what energy is required to cause the oxygen molecule to split. They showed that the surface structure commonly observed in bulk gold—a hexagonal pattern—does not hold onto oxygen very strongly, and the oxygen’s structure is not deformed. That means it still takes a lot of energy to split the oxygen molecule into two atoms that are ready to react. On the other hand, if the gold structure is a square pattern, oxygen molecules readily stick to the surface and are deformed to the point of splitting, leaving them available to react (indeed, under these conditions, gold will oxidize as well). The researchers estimate that the square lattice gold surface is as active as common catalytic metals, such as platinum. Gold surfaces are also quite active in the sense that gold atoms will readily rearrange themselves on the surface. By shuffling around, they change an exposed flat square lattice into a slightly rougher inactive hexagonal lattice. But the change, called surface reconstruction, can’t happen in just any way. Instead, the atoms move to form a 2D repeating structure that covers the exposed face, and the area required to form a complete unit of the repeating structure is quite large. On a chunk of gold, this is not an issue because there are plenty of atoms to go around, so each surface ends up almost completely inert. On nanoparticles, the story is different. The limited number of atoms means there are not enough atoms or space for surface reconstruction. So a material known for its inertness suddenly shows its true colors and starts to react and act as a catalyst. These studies show just how intricate the details of surface chemistry and catalysis can be. Inert metals become active and then return to inertness simply due to a change in material volume. It also opens new avenues for research on catalysis, though I don’t imagine gold will become the catalyst of choice any time soon. Physical Review Letters, 2026, DOI: 10.1103/g3bc-t1qv