Plasma-Assisted Catalytic Reduction of NOx

Abstract

<div class="htmlview paragraph">Many studies suggest that lean-NO<sub>x</sub> SCR proceeds via oxidation of NO to NO<sub>2</sub> by oxygen, followed by the reaction of the NO<sub>2</sub> with hydrocarbons. On catalysts that are not very effective in catalyzing the equilibration of NO+O<sub>2</sub> and NO<sub>2</sub>, the rate of N<sub>2</sub> formation is substantially higher when the input NO<sub>x</sub> is NO<sub>2</sub> instead of NO. The apparent bifunctional mechanism in the SCR of NO<sub>x</sub> has prompted the use of mechanically mixed catalyst components, in which one component is used to accelerate the oxidation of NO to NO<sub>2</sub>, and another component catalyzes the reaction between NO<sub>2</sub> and the hydrocarbon. Catalysts that previously were regarded as inactive for NO<sub>x</sub> reduction could therefore become efficient when mixed with an oxidation catalyst. Preconverting NO to NO<sub>2</sub> opens the opportunity for a wider range of SCR catalysts and perhaps improves the durability of these catalysts. This paper describes the use of a non-thermal plasma as an efficient means for selective partial oxidation of NO to NO<sub>2</sub>. When combined with some types of SCR catalyst, the plasma can greatly enhance the NO<sub>x</sub> reduction and eliminate some of the deficiencies encountered in an entirely catalyst-based approach.</div>