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Sustainable Energy

A Less Resource-Intensive Way to Make Ethanol

Stanford researchers develop a copper catalyst that can efficiently convert carbon monoxide and water to ethanol.

Producing ethanol from renewable electricity would reduce the amount of land and water needed to make biofuels.

Today, nearly all ethanol fuel is made from corn or sugarcane, which requires vast tracts of land and huge quantities of water and fertilizer. Researchers at Stanford University have now developed an electrochemical process that could be far cheaper and better for the environment.

The work is still experimental, but it’s significant because the group was able to synthesize ethanol and other desired products with so little energy input. “The levels of activity for CO reported here are unprecedented and a large step toward the realization of a practical system for converting CO to ethanol,” says Clifford Kubiak, professor of chemistry and biochemistry at the University of California, San Diego.

The scientists created a copper-based catalyst that is very effective at producing ethanol and other carbon compounds from carbon monoxide and water in a simple chemical reaction. They say the process, described in a paper published in Nature on Wednesday, could be powered by renewable sources of electricity, such as solar and wind, and would be an alternative to traditional biofuel production.

Making ethanol is normally remarkably energy-intensive, involving gathering and treating biomass and then fermenting the sugar found in the plant matter. The Stanford paper shows it’s feasible to produce ethanol directly from water and waste gases using an electric current.

“You get the same fuel, although in principle it could be much more efficient because you are not relying on biomass,” says Matthew Kanan, an associate professor of chemistry at Stanford who co-authored the paper.

The researchers envision a two-step process in which carbon dioxide is first converted into carbon monoxide using either existing processes or more energy-efficient ones currently under development. Then the carbon monoxide would be converted to ethanol or other carbon-based compounds electrochemically.

Existing methods for turning carbon monoxide into fuel are complicated, requiring very large reactors and high pressures. An electrolyzer, which uses an electrical current to drive a chemical reaction, could make the required system much smaller, says Joel Rosenthal, an assistant professor at the University of Delaware. This could allow ethanol production to be miniaturized and distributed.

One could image, for example, having a rooftop solar panel produce liquid fuel stored in a tank the size of a water heater. “The big value of chemical fuels in general, and liquid fuels in particular, is that they have much, much higher energy density than typical battery technologies, so you can store a lot more energy in a smaller amount of space,” Rosenthal says.

Ib Chorkendorff, the director of the Catalysis for Sustainable Energy research center at the Technical University of Denmark, describes the work as “an important step towards the goal of finding an efficient route for storing electricity as chemical energy.”

The key to the new catalyst is preparing the copper in a novel way that changes its molecular structure. Until now, copper catalysts produced a wide range of carbon-based compounds, rather than one desired product, and required a lot of energy.

The Stanford group starts with copper metal and, by heating it in air, grows a layer of copper oxide on top. Then that surface layer is chemically converted back to metallic copper. In the process, the copper takes on a very different surface with more active area for it to act as a catalyst.

It will take years to know whether a device based on this chemistry would be commercially viable. But if perfected, it could provide an economic incentive for removing carbon dioxide from the atmosphere. 

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