Optimum NO2/NOx ratio for efficient selective catalytic reduction

A new method of using ozone generator to improve selective catalytic reduction of nitrogen oxides (NOx) was investigated. In most practical exhaust gases, NOx (NO plus NO2) consists mainly of NO. Injecting ozone into the exhaust gas as a means for the oxidation of NO to NO2, it was experimentally shown that the catalytic reduction of NOx was remarkably enhanced. For the present study, a dielectric barrier discharge device using ac high voltage was employed to produce ozone, which was continuously fed to the exhaust gas. The experiments were primarily concerned with the influence of the NO2/NOx ratio on the catalytic reduction of NOx. The effect of reaction temperature, water vapor content, oxygen content, initial NOx concentration, and ammonia concentration on the catalytic reduction of NOx under various NO2/NOx ratios were examined. The changes in the NO2/NOx ratio as a result of the ozone injection into the exhaust gas were found to largely improve the catalytic reduction of NOx, especially at low temperatures (Authors)