The Department of Defense (DoD) needs to develop innovative technologies for reducing nitrogen-base demissions from mobile and stationary sources such as – aircraft engine exhausts, mobile heavy equipment, and diesel generators – to comply with Federal and local regulations arising from the Clean Air Act (CAA) and the CAA Amendments of 1973 and 1990.

This project will further develop and optimize Selective Catalytic Reduction (SCR) technology by using a non-thermal plasma (NTP) pretreatment to augment the oxidation and subsequent catalytic destruction of nitrogen oxides in combustion exhaust gases.

Technical Approach

In the SCR process, destruction of partially oxidized nitrogen-containing contaminants (NOx) present in combustion exhausts proceeds by catalytic oxidation of NOx to nitrogen dioxide (NO2) which is subsequently reduced to nitrogen (N2) by an added reducing agent, usually ammonia or a derivative, in the presence of a second catalyst. Because NOx is oxidized along with hydrocarbons (HC) in an NTP, treating the inflow with the NTP creates reactive species that enhance destruction of NO2 by the SCR catalyst.


A full-scale engineering prototype SCR/NTP system to evaluate the treatment of exhaust from a 6-L diesel engine has been designed and is being assembled in preparation for long-term testing. Projections of the cost/benefit of a full-scale control process are favorable. After initial benchtop studies using propene as the reductant, bench-and pilot-scalestudies on splits of diesel exhaust using diesel fuel as the reductant have achieved less-efficient but still practical conversion of NOx into N2, carbon dioxide (CO2), and water. The extent of NOx conversion appears to be independent of scale, and the process does not appear to be affected by fuel sulfur. A tentative design for a field-ready unit has been prepared.


Augmentation of the SCR process by NTP increases the efficiency of removal of NOx and decreases the consumption of power and of added reducing agent. More importantly, it permits use of engine fuel HCs as the reducing agent instead of requiring a separate supply of ammonia or some other nonstandard hazardous material.