By tuning gold nanoparticles to just the right size, researchers from
"Our study shows potential of carefully designed gold nanoparticles to recycle CO2 into useful forms of carbon," said
The findings are published in the
The idea of recycling CO2 -- a greenhouse gas the planet current has in excess -- is enticing, but there are obstacles. CO2 is an extremely stable molecule that must be reduced to an active form like CO to make it useful. CO is used to make synthetic natural gas, methanol, and other alternative fuels.
Converting CO2 to CO isn't easy. Prior research has shown that catalysts made of gold foil are active for this conversion, but they don't do the job efficiently. The gold tends to react both with the CO2 and with the water in which the CO2 is dissolved, creating hydrogen byproduct rather than the desired CO.
"At first, that result was confusing," said
To understand what was happening, Peterson and postdoctoral researcher
"When you take a sphere and you reduce it to smaller and smaller sizes, you tend to get many more irregular features -- flat surfaces, edges and corners," Peterson said. "What we were able to figure out is that the most active sites for converting CO2 to CO are the edge sites, while the corner sites predominantly give the by-product, which is hydrogen. So as you shrink these particles down, you'll hit a point where you start to optimize the activity because you have a high number of these edge sites but still a low number of these corner sites. But if you go too small, the edges start to shrink and you're left with just corners."
Now that they understand exactly what part of the catalyst is active, the researchers are working to further optimize the particles. "There's still a lot of room for improvement," Peterson said. "We're working on new particles that maximize these active sites."
The researchers believe these findings could be an important new avenue for recycling CO2 on a commercial scale.
"Because we're using nanoparticles, we're using a lot less gold than in a bulk metal catalyst," Sun said. "That lowers the cost for making such a catalyst and gives the potential to scale up."
The work was funded by a
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