Opportunity NOx

Pacific Northwest National Laboratory researchers put their expertise in surface science and catalysis to work when they developed an effective plasma catalysis system for treating engine exhaust one of the first advanced emissions control technologies developed by the Laboratory.

This technology combines an electrically energized gas, called plasma, with a specialized catalyst material to convert oxides of nitrogen (NOx) into components of clean air. Researchers began developing vehicle emission reduction technologies in the early 1990s, with funding from a government program focused on improving fuel efficiency and reducing emissions in light-duty vehicles.

After trying plasma and catalyst methods separately, PNNL scientists took a unique approach. They combined the techniques into a two-phase process that applies non-thermal plasma processing to the exhaust stream before passing it through a specialized catalyst system. In laboratory tests, PNNL's non-thermal plasma catalysis for engine exhaust treatment reduces NOx emissions by as much as 90 percent.

PNNL and industry collaborators have developed a system that converts harmful oxides of nitrogen in vehicle exhaust into components of clean air. Vehicle exhaust, loaded with nitric oxides, flows into the non-thermal plasma reactor, where it is converted into nitrogen dioxide. A catalyst is then responsible for a chemical reaction that reduces nitrogen dioxide into harmless nitrogen gas. An optional filter also reduces particulate matter. PSA Peugeot Citroën installed this system in their Peugeot 206 environmental demonstration vehicle.

"This concept of using a non-thermal plasma to activate catalysis has only existed for about seven or eight years," said PNNL's Chuck Peden, who leads interfacial chemistry and engineering research. "Today, it is recognized as a potential commercial solution."

The specialized solid catalyst developed at PNNL to optimize chemical reactions that reduce NOx in plasma catalyst systems won an R&D 100 award in 2001, recognizing it among the top 100 technology advances of 2000.

The catalyst since has been fine-tuned even further and PNNL researchers are working with Delphi Corp. on designs for a commercial product based on non-thermal plasma technology. Delphi and PSA Peugeot Citroën have been developing a non-thermal plasma system specifically designed for Peugeot vehicles.

Researchers also are working on reducing the system's power requirements. This is important because most emission reduction technologies negatively impact fuel efficiency. "The more efficient the system is, the less impact there will be on the operation of the vehicle, and therefore, the more transparent it will be to the consumer," said Darrell Herling, a senior development engineer.