New catalyst helps eliminate NOx from diesel exhaust
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ARGONNE, Ill. (April 27, 2007) — A catalyst developed by Argonne researchers
could help diesel truck manufacturers eliminate harmful nitrogen-oxide emissions
from diesel exhausts.
The pattented technology appears
so promising that multiple large and small companies have expressed interest
in licensing it and working with Argonne researchers to scale up the technology
and bring it to market. Argonne researcher Christopher Marshall, one of the
technology's developers, believes there could be a commercially available product
within two to three years.
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. For example,
many technologies that reduce NOx result in increases in undesirable particulate
emissions.
"For diesel engines, we envision manufacturers placing ceramic catalytic
reactors in the exhaust pipes, where they will convert NOx emissions into nitrogen," said
Marshall, who works in Argonne's Chemical Engineering Division. Nitrogen, or
N2, 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
with copper ions attached within its micropore structure. Zeolites are common
catalysts in the petroleum industry.
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 diesel exhaust temperatures and don't work
well in the presence of water vapor, which is almost always found in engine
exhausts.
With the help of the Advanced Photon Source at Argonne to analyze the structure and performance of
various catalysts, Marshall's group at Argonne developed an additive that
allows Cu-ZSM-5 and similar catalysts to overcome these difficulties.
"Our new cerium-oxide additive," Marshall 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
95-100 percent of NOx emissions."
Argonne's new catalyst also avoids the problems associated with ammonia,
which competing catalysts use as the reductant. The Argonne catalyst uses
the diesel fuel that is already on board thereby requiring no additional tankage.
"Another type of technology is ammonia-selective catalytic reduction,
using a material called urea as the ammonia source," Marshall said. "Ammonia
is toxic, and unless all of it is converted during the process, whatever remains
could be 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 and uses the onboard diesel fuel as the reductive material, the new catalyst
is considered safer and more energy-efficient.
Another alternative for U.S. manufacturers is the use of NOx traps. These
are platinum-based systems that work well if they don't come into contact with
sulfur, which is present in most commercial diesel fuel. Since the Argonne-developed
catalyst contains no platinum, it is degraded far less by the fuel-borne sulfur.
Marshall says the Argonne catalyst has been tested and performed well with
a number of diesel and diesel-type fuels, including standard diesel, synthetic
diesel, bio-diesel and JP8, which is a jet fuel preferred by the military.
Having performed well in these tests, the next step is to subject the catalyst
to engine testing. This will take place soon at Argonne's Diesel Engine Test
Facility. Marshall expects these tests will show that in addition to its other
advantages, the Argonne catalyst has a greater life expectancy than other catalysts
currently on the market.
Marshall and his colleagues are also working with the Chemical Engineering
Division's fuel cell research group. Using a reformer developed by this group
could provide better fuel for the catalyst, said Marshall. "Our catalyst
already works well, but it would work even better with the smaller hydrocarbons
produced by a reformer. Collaborations like this and access to Argonne's unique
facilities allow us to work together on projects in a way that couldn't be
done anywhere else."
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.
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the world's brightest scientists and engineers together to find exciting and
creative new solutions to pressing national problems in science and technology.
The nation's first national laboratory, Argonne conducts leading-edge basic
and applied scientific research in virtually every scientific discipline. Argonne
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and federal, state and municipal agencies to help them solve their specific
problems, advance America 's scientific leadership and prepare the nation for
a better future. With employees from more than 60 nations, Argonne is managed
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the U.S.
Department of Energy's Office
of Science.
For more information, please
contact Steve McGregor (630/252-5580 or media@anl.gov)
at Argonne.
By Donna Jones Pelkie
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