Plasma depollution

Plasma depollution: would it be a solution for the future? (inspired by The Research, February 1999)

Keywords: treatment, exhaust gases, pollution, plasmas, catalyst.

Gaseous emissions from diesel engines are more and more severely limited by European standards. To achieve compliance, new technologies are developed.

For trucks, there are very efficient catalysts, such as those in which ammonia, coming from hydrolyzed urea, acts as a reducing agent. But they must operate at high temperatures, usually above 200 ° C. However, these temperatures are not reached by the exhaust gases of passenger cars when starting up or during urban journeys.


This catalyst developed by Siemens consists of electrodes between which a plasma is created. It measures approximately 20 cm long and 6 cm in diameter. (Siemens photo, II / 98).

Unless you resort to additional heating of the gases, which would be energetically very expensive, the solution passes through another purification route. To do this, the Siemens Group, in collaboration with the German Ministry of Research, has developed a plasma phase catalysis process.

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Reduction of nitrogen oxides in exhaust gases at 220 ° C of a diesel engine through dielectric and plasma discharges

The principle is to bring the exhaust gases into contact with a plasma whose high energy electrons will initiate, on the one hand, the oxidation of carbon compounds into carbon dioxide and water and, on the other hand, the reduction of nitrogen oxides to nitrogen. Plasma is obtained only by causing a brief electrical discharge (a few nanoseconds) within the gas. But the efficiency of this process decreases considerably when the water and oxygen content becomes high, the reduction of nitrogen oxides then being very disadvantaged.


Reduction of NOx according to the technology used.

To remedy this problem, the researchers placed this system in series with a conventional catalyst of the type of those mentioned above. They observed that, thanks to this association, it operated at temperatures below 200 ° C. For example, the reduction in oxide emissions is estimated at 60% if the temperature is only 100 ° C. The quantity of urea to be hydrolyzed is also much less under these conditions. The first tests are carried out at the University of Erlangen. The time needed to develop prototypes, and develop a high-performance power supply to ensure the discharge is estimated at six or seven years. To learn more about this technology, visit the Siemens website

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Research still in progress

Despite the date of this article, 1999, research is still ongoing, including CNRS here is a summary document: Decontamination of gaseous effluents by Plasma (CNRS and GREMI)

The French manufacturers Renault and PSA have recently co-filed a patent entitled: Non-thermal plasma reactor and motor vehicle exhaust line comprising this reactor

Summary documents:

- Original article by Siemens (German)
- Depollution of gaseous effluents by Plasma (by GREMI, University of Orléans and CNRS)
- PSA-Renault patent (member-only download)
- Visit the GREMI website

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