Developed by the U.S. Department of Energy's Argonne National Laboratory, the new catalyst is one of a family of related catalysts that also shows promise for reducing NOx emissions from industrial sources, such as coal-fired power plants and furnaces at chemical plants and refineries.
Nitrogen oxides -- collectively called "NOx" -- contribute to smog, acid rain and global climate change.
"For diesel engines, we envision manufacturers placing ceramic catalytic reactors in the exhaust pipes, where they will convert NOx emissions into nitrogen," said inventor Chris Marshall of Argonne's Chemical Engineering Division. Nitrogen is a harmless gas that makes up more than 80 percent of the Earth's atmosphere.
"Our most promising catalyst for diesel engines," Marshall said, "is Cu-ZSM-5 with an external coating of cerium oxide." Cu-ZSM-5 is a zeolite doped with copper; zeolites are common catalysts used in petroleum refining.
Those working previously with Cu-ZSM-5 and similar catalysts, he said, found that they performed poorly at removing NOx from diesel exhaust. They require temperatures higher than normal exhaust temperatures and don't work well in the presence of water vapor, which is almost always found in engine exhausts.
"Our new cerium oxide additive," he said, "is the breakthrough that makes it work. When it's combined with Cu-ZSM-5, the resulting catalyst works at normal exhaust temperatures and is actually more effective with water vapor than without it. With a lean fuel-air mixture, it removes as much as 95 to 100 percent of NOx emissions."
Argonne's new catalysts also avoid the problems associated with ammonia, which competing catalysts generate.
"The current standard is ammonia-selective catalytic reduction, using urea as the source," Marshall said, "but ammonia is toxic, and unless all of it is converted during the process, whatever remains is released to the atmosphere. While some European diesel manufacturers are taking the urea approach, U.S. diesel manufacturers are looking for alternatives." Since a system using the new catalyst would not require an on-board urea storage tank, the new catalyst is considered safer and more energy-efficient.
"We're also looking at other elements that may work better than cerium under certain engine conditions," he said. "Zirconia shows good promise."
Initial research on the cerium-oxide catalyst was funded by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy. The catalyst was developed for chemical plant emissions under a joint research agreement with BP. Research plans call for expanded work aimed at both diesel and natural gas engines and coal-fired power plants.
A patent application has been filed on the new catalyst and it is expected to be available for licensing.
The nation's first national laboratory, Argonne National Laboratory conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology. Since 1990, Argonne has worked with more than 600 companies and numerous federal agencies and other organizations to help advance America's scientific leadership and prepare the nation for the future. Argonne is operated by the University of Chicago for the U.S. Department of Energy's Office of Science.
For more information, please contact Catherine Foster (630-252-5580 or media@anl.gov) at Argonne.