CARBON DIOXIDE emissions could be turned back into a fuel.
ALEXANDER RUESCHE/EPA/CORBIS

Carbon dioxide is part of nearly everything humans do. It comes out of the tailpipes of our cars, the stacks from most of our power plants and the nostrils on the tail end of every breath we take. From a climate change perspective, of course, all this CO₂ is a problem, given the greenhouse property of the gas. A variety of solutions have been proposed, including burying the stuff deep below the earth or sea or switching to fuels that do not lead to its emission, but now a scientist from Italy has offered another possibility: turn it back into fuel.

Chemist Gabriele Centi of the University of Messina in Italy uses solar energy gathered by a titanium dioxide film to ionize CO₂ in its liquid form. Mixing this ionized liquid carbon dioxide with water, chemists can create longer carbon chains, much like photosynthesis in plants. In current tests the process can create some natural gas and methanol, but the number and type of carbon chains cannot be controlled. ¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿

Centi's team decided to try to use carbon dioxide in its natural form: gas. In a device much like a fuel cell, known as a photoelectrocatalytic reactor, the researchers tested several potential catalysts, ranging from copper to carbon nanotubes. In each case, the process turned CO₂ into more complex carbon molecules. Most intriguingly, depending on the catalyst involved, the researchers could create hydrocarbons with as many as nine carbon atoms--the kinds of useful fuels produced by industry using the so-called Fischer-Tropsch reaction--and with some control over the amount made. Further, by placing iron molecules within the carbon nanotubes, the process could be made even more efficient, though not as much as using expensive platinum or palladium. "It is a long time to practical applications," Centi says. But he notes it might prove useful on a manned mission to Mars, which cannot easily carry enough fuel for its return, to be able to make it on the Red Planet itself. Centi presented his new gas phase research on September 13 at the American Chemical Society meeting in San Francisco.