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Argonne’s deNOx Catalyst Begins Extensive Diesel Engine Exhaust Testing

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Argonne’s deNOx catalyst can be prepared as a powder or a monolith.
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Principal investigator Chris Marshall shows the monolith form of the Argonne deNOx catalyst with a sensor inserted for testing.
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Mechanical engineer Doug Longman inserts the instrumented deNOx catalyst monolith into the aftertreatment chamber of Argonne’s heavy-duty Caterpillar diesel test engine.

Background

Diesel engines, while efficient, produce many undesirable combustion byproducts in their exhaust. While we tend to think of the sooty exhaust products we see as the bad stuff, it is the less-visible exhaust products such as nitrogen oxides (NOx) that create bigger problems.

According to the U.S. Environmental Protection Agency, “Nitrogen Oxides are a family of poisonous, highly reactive gases. These gases form when fuel is burned at high temperatures. NOx pollution is emitted by automobiles, trucks and various non-road vehicles (e.g., construction equipment, boats, etc.) as well as industrial sources such as power plants, industrial boilers, cement kilns, and turbines. NOx often appears as a brownish gas. It is a strong oxidizing agent and plays a major role in the atmospheric reactions with volatile organic compounds (VOC) that produce ozone (smog) on hot summer days.”(1)

Many state and federal laws have been enacted during the last two decades to reduce NOx emissions from vehicle and stationary sources. It is likely that such rules will become even more restrictive during the next decade. Since diesel truck engines tend to emit higher levels of NOx than other types of engines, they are an attractive research target for reducing NOx emissions.

Argonne’s Research

Argonne National Laboratory’s chemists have been working to identify new approaches to treating NOx before it reaches the atmosphere. Catalysts that transform the NOx into something less noxious look very promising. Catalysis produces a chemical reaction between two or more substances or gases, transforming them into other substances or gases. In nature, enzymes are the ultimate catalysts, facilitating processes such as digestion, decomposition, fermentation, to name just a few. For treating engine exhaust, catalysts typically employs a reductant (such as urea or in our case, diesel fuel) plus a combination of elements on a substrate (support) to transform gases like NOx into more benign outputs like nitrogen (N2), carbon dioxide (CO2), and water (H2O).

In 2007, Argonne patented a deNOx catalyst that has strong potential for use in onboard emissions treatment systems. (2) The Argonne deNOx catalyst relies on selective catalytic reduction using cerium oxide coated over a zeolite (ZSM-5) and copper (Cu) substrate to produce a flexible, stable, and effective means of treating NOx in diesel exhaust. According to the project’s principal investigator, Chris Marshall, “Cu-ZSM-5 is a zeolite with copper ions attached within its micropore structure. Those working previously with Cu-ZSM-5 and similar catalysts 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 always found in engine exhausts. Our cerium-oxide additive,” Marshall said, “is what makes it all 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 (as in diesel engines), our catalyst removes as much as 95% of NOx emissions.”

Having shown promising results in the lab, it is time now for the Argonne deNOx catalyst to prove its mettle where it matters--in Argonne’s Engine Research Facility. Starting in November 2012, Argonne engine researchers began testing the deNOx catalyst in a variety of diesel engine exhaust aftertreatment configurations in the facility’s heavy-duty Caterpillar diesel engine, in order to generate data that will help potential licensees of the technology determine if it is an appropriate solution for their needs. Because the deNOx catalyst is adaptable for use in a variety of “as-designed” and retrofit applications, testing focuses on using the catalyst as a coating over a monolith, which could be used inside the diesel exhaust system.

Once testing is complete and results verified, data will be available through Argonne’s Technology Development and Commercialization Division.

References

  1. U.S. Environmental Protection Agency, “Nitrogen Oxide (NOx) Control Regulations.”
  2. U.S. Patent Number 7,220,692, “Catalyst for Selective NOx Reduction Using Hydrocarbons,” issued to C. L. Marshall and M. K. Neylon, May 22, 2007.
Contact

Christopher Marshall
marshall@anl.gov


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