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August 24, 1998This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. PREPRINT ABSTRACTMuch work has been done on the application of plasmas to the treatment of NO x from power plants. In power plant applications, the purpose of the plasma is to oxidize NO to NO 2 , 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 N 2 . This paper will discuss the results of an extensive series of experiments aimed towards understanding the effect of gas composition on the NO x conversion chemistry in a plasma. The NO x conversion chemistry in the presence of the individual components, such as N 2 , O 2 , H 2 O, and CO 2 , as well as the mixture of these, will be presented. We will show that, in a leanburn gasoline or diesel engine exhaust, the main effect of the gas-phase reactions in a plasma is the oxidation of NO to NO 2 and nitric acid. To implement the reduction of NO x to N 2 in the highly oxidizing environment of a lean-burn engine exhaust, it will be necessary to prevent the formation of acid products and combine the plasma with another process that can chemically reduce NO 2 to N 2 .

Experiments were conducted in a benchtop apparatus and a process development unit. The parameters investigated included applied voltage, frequency, packing, the chemical composition of the gas stream, and flow conditions in the barrier discharge reactor. Experimental results showed that conversion of nitric oxide increased to greater than 85% as the peak voltage was increased from 7 to 15 kV. Similarly, conversion increased to greater than 95% as frequency was increased from 60 to 1000 Hz. Products of the reactions leading to nitric oxide destruction were nonpolluting nitrogen and oxygen when a dry mixture of NO and N 2 was used as inlet gas. Addition of oxygen and carbon dioxide lowered the NO x conversion. Nitric acid was produced when the gas stream contained water vapor. Results of this work have the potential to establish the foundation for a nitrogen oxides control technology that may be technically and economically feasible.

August 1998This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. PREPRINT