New breakthrough in producing renewable fuels from CO2

A team of chemists have discovered a new way to produce carbon-based liquid fuels from CO₂.

The new additive, identified by a team of scientists from the California Institute of Technology (Caltech), selectively converts CO_{2 ­}fuels containing multiple carbon atoms, a step towards producing renewable liquid fuels which are not derived from coal or oil.

"The results were quite shocking," says Jonas Peters, Bren Professor of Chemistry at Caltech and director of the Resnick Sustainability Institute, who jointly led the research in collaboration with Theodor Agapie, professor of chemistry at Caltech. "Usually, in these types of reactions with CO₂, you see a lot of by-products like methane and hydrogen. In this case, the reaction was highly selective for the more desirable fuels that contain multiple carbons -- such as ethylene, ethanol, and propanol. We saw an 80 percent conversion to these multi-carbon fuel products, with only 20 percent or so going into hydrogen and methane."

Postdoctoral scholars Ruud Kortlever and Hsiang-Yun Chen and former postdoc Zhiji Han, carried out the research under the supervision of Peters and Agapie. The results have been published in ACS Central Science.

To find the perfect combination for making multicarbon fuels, the team experimented with a mix of different chemicals in the lab. They used an aqueous solution and a copper electrode, which served as both a catalyst and source of energy in place of the sun. The group added CO₂ to an aqueous solution and a copper electrode, as well as a class of organic molecules called N-substituted arylpyridiniums, which formed a very thin deposit on the electrode. This film, dramatically improved the fuel-making reaction, selectively producing the desirable chemicals ethanol, ethylene, and propanol.

"It's easy to make hydrogen under these conditions, so usually we see a lot of it," says Agapie. "But we want to disfavor the hydrogen production and favor high-energy density liquid fuels with carbon-carbon bonds, which is exactly what we get in our experiments."

The next step is for the team to determine how the additives enhanced the reaction. They also plan to test different additives, to see if they can further improve the selectivity for the desired fuels.

Ultimately, the team hope that the information they’re gaining could contribute towards the development of alternative fuels made from sunlight, CO₂ and water, instead of oil.

"Nature has stored solar energy in the form of oil over a long period of earth history via a process that takes millions of years," says Peters. "Chemists would like to figure out how to do this much faster."