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Chemist Chris Marshall shows a new catalyst developed by Argonne and BP to reduce nitrogen oxides from diesel engines. |
New catalyst knocks out NOx emissions |
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New catalysts, developed by Argonne in collaboration with BP, could help auto makers meet the U.S. Environmental Protection Agency’s deadline to eliminate 95 percent of nitrogen-oxide emissions from diesel exhausts by 2007. Other nations have similar deadlines in 2006. These new catalysts can also reduce nitrogen-oxide 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 warming. Yet they are among the most difficult pollutants to eliminate from diesel exhaust, because most technologies that reduce NOx also increase undesirable particulate emissions. The new catalysts overcome hurdles that until recently frustrated researchers. “Our research uses catalysts to help convert NOx in the exhausts to nitrogen, a safe gas that makes up about 80 percent of the air we breathe,” said Argonne chemist Chris Marshall. A small amount of diesel fuel is injected into the engine’s exhaust stream where the catalyst helps hydrogen in the fuel remove oxygen from NOx. Until recently, this approach has encountered problems. The best commercial catalysts, Marshall said, use ammonia. “Not only is ammonia difficult to store, but if conversion is incomplete, ammonia can be released to the atmosphere. This is worse than NOx.” A promising early catalyst that did not use ammonia was Cu-ZSM-5, a zeolite with copper ions attached within its micropore structure. Zeolites are common catalysts in the petroleum industry. “Unfortunately,” Marshall said, “catalysts like this one don’t work well in the presence of water vapor, which is almost always found in engine exhaust. They also work only at temperatures higher than normal exhaust temperatures.” With the help of the Advanced Photon Source to analyze the structure and performance of various catalysts, Marshall’s group at Argonne developed a proprietary additive that allows Cu-ZSM-5 and similar catalysts to overcome these difficulties. “When our additive is combined with Cu-ZSM-5,” he said, “the resulting catalyst works at normal exhaust temperatures and is actually more effective with water vapor present than without it.” With a lean fuel-air mixture, it removes as much as 95 to 100 percent of NOx emissions. The new catalysts were developed for chemical plant emissions under a joint research agreement with BP. Success has led to expanded work to reduce NOx emissions from coal-fired power plants, funded by the U.S. Department of Energy’s Office of Fossil Energy. Researchers are also investigating the catalyst in diesel automobile engines. For more information, please contact David Baurac. |