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Much work has been done on the application of plasmas to the treatment of NOx from power plants. In power plant applications, the purpose of the plasma is to oxidize NO to NO2, and eventually to nitric acid. The desired products, in the form of ammonium salts, are then obtained by mixing ammonia with the formed acids. Some form of scrubbing is required to collect the final products. For applications to the treatment of exhausts from cars and trucks, it is very important to make a distinction between NO removal by chemical oxidation and NO removal by chemical reduction. To avoid the need for scrubbing of plasma processing products, the desired method of NO removal is by chemical reduction; i.e. the conversion of NO to benign gaseous products like N2. This paper will discuss the results of an extensive series of experiments aimed towards understanding the effect of gas composition on the NOx conversion chemistry in a plasma.

This paper presents the results of experiments in which various parameters were varied systematically in an attempt to understand how the reactor design affects the energy efficiency for plasma processing of NOX. These parameters include the packing material, electrode diameter, and voltage frequency. It is shown that the applied voltage is not the relevant parameter when comparing the performance of different plasma reactors. The important control parameter is the input energy density. In accordance with the observations reported by Penetrante et al. [Applied Physics Letters 68, 3719-3721 (1996)], we have found that reactor design has little influence on the basic energy consumption of the plasma. Consequently, different reactor designs should yield basically the same plasma chemistry if the experiments are performed under identical gas composition and temperature conditions.