Add a molecule of carbon dioxide to one of methane, and under the right conditions, these potent greenhouse gases rearrange themselves into two molecules of carbon monoxide and two of hydrogen — a combination called syngas, a widely used feedstock. But this sought-after reaction demands not only a chemical catalyst, but also temperatures between 700 and 1,000 ºC.

Researchers now show that light, not heat, might be a more effective fuel for this energy-hungry reaction. Naomi Halas at Rice University in Houston, Texas, and her collaborators developed a light-stimulated catalyst that conducts the reaction without heat input.

The researchers engineered catalyst particles to contain precisely one ruthenium atom for every 99 copper atoms. Under intense white light from a laser, the copper delivers hot electrons to the ruthenium atoms, where the reaction takes place. These electrons power the reaction.

If the reaction is performed in the dark, it slows to less than one-quarter of the light-powered rate, even at high temperatures.