21st Century Alchemist’s Gold

Remember how we learned that alchemists tried to turn other elements into gold? That wasn’t too plausible back then; they needed a greater knowledge of science to realize that it was nearly impossible to alter the number of protons in an atom to make it gold.

These days, a more coveted transformation would be to turn carbon dioxide, which the earth has a bit too much of, into fuel or useful industrial chemicals. Researches from Brown have shown that by maximizing the long edges of gold nanoparticles, they may make better catalysts for CO2 recycling.
Click here for the article on phys.org.

“Our study shows potential of carefully designed gold nanoparticles to recycle CO2 into useful forms of carbon,” said Shouheng Sun, professor of chemistry.

 

CO2 is a very stable molecule, however, and much be reduced to an active form like CO to be useful. CO is used to make synthetic natural gas, methanol, and other alternative fuels, but converting CO2 to CO is not easy. Gold foil has been used for this conversion, but rather inefficiently, as gold tends to react with both CO2 and the water it is dissolved in, creating a hydrogen byproduct rather than CO.

The Brown experimental group shrank the gold down to nanoparticles to make it more selective for CO2.

The size of these gold nanoparticles is crucial, because edges produce more desired results than corners.

That’s very interesting to me! Since nanoparticles are so… well, nano, I imagine them to be so small that I’ve never really thought about how some might have relatively longer “edges” to them than others. According to the article, Nanoparticles of 8 nm appear to have a better edge-to-corner ratio than 4 nm, 6 nm, or 10 nm nanoparticles. Eight nanometer particles achieved a 90% rate of conversion from CO2 to CO. How cool!

“What we were able to figure out is that the most active sites for converting CO₂to CO are the edge sites, while the corner sites predominantly give the by-product, which is hydrogen. 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.” said Andrew Peterson, professor of engineering.

The researchers believe these findings could be an important new avenue for recycling CO₂ on a commercial scale. They are now working on new particles to maximize the active sites on these nanoparticles.