Award-winning gasoline reformer is a catalyst for change
fuel processor reforms ordinary gasoline into hydrogen-rich gas for fuel cells
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Instead of spark plugs and cylinders, environmentally friendly fuel cell engines may be under the hoods of the cars of the future. But first, scientists must find a practical and economical way to supply the hydrogen gas needed to power them. Chemical engineers at Argonne have developed and patented a compact fuel processor that “reforms” ordinary gasoline into a hydrogen-rich gas to power fuel cells. The technology was recently named one of the top 100 inventions of the year by R&D magazine.
Fuel cells convert hydrogen gas into electricity and water. Compared to internal combustion engines, the energy conversion is clean and efficient. “You can think of fuel cells as batteries that are continuously charged by supplying fuel,” said Jim Miller, manager of Argonne’s Electrochemical Technology Program.
A team of scientists in the Chemical Technology Division, led by Mike Krumpelt and Shabbir Ahmed, have synthesized new types of catalysts to form hydrogen by reacting gasoline with oxygen. Catalysts are materials that speed chemical reactions by cutting the energy required to start the reaction. While catalysts help some chemical bonds form and others break, catalysts remain unchanged. Using the Argonne catalyst, Ahmed designed and built an inexpensive, easy-to-manufacture fuel-reforming reactor.
Don’t burn it, reform it
Fuel cell engines are clean. They efficiently convert hydrogen and oxygen into electric power with water and heat as the only by-products. The fuel cell is expected to be 60 percent efficient — twice as efficient as today’s internal combustion engines. And fuel cells should cut carbon dioxide output to half that of a combustion engine.
Using hydrogen directly to power fuel cell engines would be environmentally ideal, but it is not practical today. Hydrogen-storage devices are heavy and bulky, and no retailing infrastructure exists for supplying hydrogen to consumers. These challenges prompted scientists to investigate compact processors that could produce hydrogen from conventional fuels to power the fuel cell onboard the vehicle.
Researchers originally developed methanol reformers but switched to gasoline because its production, distribution and retailing infrastructure is established. Fuel-cell car owners would use the pumps at the gas station to refuel just as they do now, but they would only need half as much gas.
History
The first fuel cells were built in 1839, but their role as a practical power generator did not emerge until the 1960s when the U.S. space program developed fuel cells to power the Gemini and Apollo spacecraft.
The space program continues to use fuel cells — they produce electricity and water for space shuttle astronauts — while fuel cell research has expanded into stationary and vehicle power generation. Argonne scientists have been involved with fuel cell research for nearly three decades.
Reformer design
In designing the fuel reformer, Ahmed used a simple, inexpensive plan similar to catalytic converters in today’s cars. Catalytic converters pass the car’s exhaust over a catalyst that converts carbon monoxide to carbon dioxide to eliminate the poisonous gas.
In Ahmed’s gasoline reformer, vaporized gasoline is mixed with steam and air and then sent through a catalyst-packed cylinder. The result is a mixture of gases with a high hydrogen concentration, which is fed to the fuel cell. Some carbon monoxide is also present in the gas mixture. Before it goes to the fuel cell, it passes through a secondary processor, which reacts water vapor and the carbon monoxide to form carbon dioxide and additional hydrogen.
Wanted: A few good catalysts
In addition to the reformer design, researchers needed new catalysts to spur the gasoline-to-hydrogen-gas chemical reaction. Hydrogen gas consists of twin hydrogen atoms bound together. The scientists needed something that could pull hydrogen atoms from the fuel molecules and combine them into the diatomic gas.
Before they found catalysts that worked well with gasoline, Krumpelt and Ahmed tried several different kinds of catalysts with no success. “Then we sweated quite a bit,” said Krumpelt.
Argonne’s work on solid-oxide fuel cells spurred them to realize that the anode (the negative electrode) could be a model for their fuel-reforming catalyst. “If these types of materials worked in a fuel cell environment,” Krumpelt reasoned, “then they should work as catalysts in the kind of reformer system we were seeking.”
Argonne scientists combined this idea with information from Argonne’s fuel cell research. Krumpelt and Ahmed used metal and oxygen compounds similar to those used in fuel-cell research as a substrate, and coated it with platinum compounds. When the gasoline/air mix contacts the catalyst, hydrogen is formed.
The researchers theorized that the supporting substrate material helps oxidize the carbon, forming carbon dioxide, and the platinum pulls the hydrogen atoms off the substrate to form the gas. Preliminary results suggested that the scientists were on the right track.
Testing…1-2-3
To test and optimize the effectiveness of the new catalyst, researchers designed a series of experiments to measure the hydrogen produced when gaseous mixtures of air, fuel and steam were passed over the platinum catalyst. The Argonne scientists wanted to find the temperature, rate of fuel and air flow, as well as the fuels that worked best with the catalyst. The sample was designed to maximize the contact between the oxygen and the catalyst. The reaction temperatures were controlled with a specialized furnace.
First, the scientists successfully tested the components of retail gasoline and then confirmed that the catalyst works with gasoline.
They found that the choices of materials for the catalyst substrate also made for some intriguing results.
“When we put the metal on an oxygen-ion-containing support, we saw a strong metal-support interaction,” said Krumpelt. “And the chemistry is different than in conventional catalysts.”
Argonne scientists are working to understand how the catalysts and reformer work and to make improvements. For example, they are experimenting with metals cheaper than platinum for the catalyst to lower the cost of the reformer. They are testing the “engineering-scale” reformer and designing a full-scale version.
A bright source yields valuable data
While the researchers don’t understand exactly how the catalyst works, experiments at Argonne’s Advanced Photon Source (APS), the country’s most brilliant source of X-rays for materials research, provided them with insights into the catalyst’s function at the atomic level. The APS work revealed that not only are chemical bonds absent between the platinum atoms during catalysis, but the platinum atoms are positive ions in a +2 charge state — meaning they are missing two of their electrons.
“It looks like individual platinum ions are doing the catalysis,” says Krumpelt.
Industry interest
While it is uncertain if fuel cell engines will replace the combustion engine, it is likely there will be more of them on the road, and fuel cells will be used in a growing number of power applications. Argonne’s reforming catalyst has been licensed to Süd-Chemie, formerly United Catalysts Inc.
Argonne researchers also have a cooperative research and development agreement with H2fuel, which is a joint venture between Unitel Technologies in Mount Prospect, Ill., and Avista Labs in Spokane, Wash. H2fuel built and tested a fuel processor designed by Argonne’s Chemical Technology Division. Through a series of catalytic reactions, this first-generation unit converted gasoline, natural gas or ethanol into a gas containing about 45 percent hydrogen. Over the next two years, H2fuel and Argonne’s Chemical Technology Division will improve this processor to the point where it is ready to enter the marketplace.
The funding for this research comes from the Department of Energy’s Office of Transportation Technologies.
For more information, please contact Catherine Foster (630/252-5580 or cfoster@anl.gov) at Argonne.