A 'novel' chemistry to make fuel from sugar
By Patrick Barry  Science News
Web edition : Thursday, September 18th, 2008

It's not alchemy, but it might sound like it: a new way to transform sugars from plants into gasoline, diesel or even jet fuel by passing the sugars over exotic materials.

This chemical trick uses nano-sized particles to produce plant-based gasoline that can be used in existing vehicles in place of petroleum-based fuels. But because they would be made from corn, switchgrass or other plants -- which absorb carbon dioxide as they grow -- the fuels would emit less net carbon dioxide than normal gasoline.

"You have a conventional fuel that happens to be made from sustainable sources," says James Dumesic, a chemical engineer at the University of Wisconsin-Madison who led the research, which appears online September 18 in Science.

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...ethanol is made by fermenting plant sugars in large, microbe-filled vats for hours or days, much like brewing beer. The new process could be simpler because it does not require keeping microbes alive, and it can convert the sugar into fuel in a matter of minutes, the team reports.

Another method for making gasoline from plant sugar exists, but it requires very high temperatures and other energy-consuming steps, making the process inefficient. The new technique requires little energy input and can convert most of the energy in the sugar into useable forms.

While the process is not yet ready for large-scale production, Dumesic's team was able to convert about 65 percent of the energy in the sugar into gasoline using their laboratory-scale process. Most of the lost energy ends up in gases such as ethane and propane, which if captured could serve as a replacement for natural gas.

An alloy of the precious metals platinum and rhenium triggers the first step of the conversion. Dumesic and his colleagues deposited 2-nanometer-wide specks of this alloy onto surfaces made of pure carbon. When a liquid mixture of water and plant sugar flows over the platinum-rhenium particles at the right temperature and pressure, the metal atoms act as catalysts to cleave chemical bonds in the sugar, releasing oxygen and leaving behind a mixture of molecules containing carbon and hydrogen -- the principal elements in gasoline and diesel.

"It's completely novel chemistry," comments Manos Mavrikakis, an expert in theoretical catalysis at the University of Wisconsin-Madison who did not collaborate with Dumesic on the new conversion process.

The molecules produced by Dumesic's catalytic reactions can be used directly to replace petroleum feedstocks that the chemical industry uses to make plastics and other materials. Or, the molecules can pass through another step of previously known catalytic reactions to produce the final fuel.

Cost of the metal catalyst could be an issue, Mavrikakis notes. "The question is how much platinum and rhenium will we need to produce the fuel we need?" he says. "These are among the most expensive metals."

Studying how the metals trigger the needed chemical reactions could enable scientists to replace the platinum and rhenium with less expensive materials, Mavrikakis suggests.