Oxidation of NO to NO2 Using the Ozonization Method for the Improvement of Selective Catalytic Reduction

Abstract

Removal of nitrogen oxides (NOx) using an ozonization and catalysis hybrid process was investigated. The role of the ozonization in the hybrid process is to increase NO2 content by oxidizing a part of NO, thereby leading to improving the performance of the catalytic reduction. It was found that the rate of the oxidation of NO to NO2 in the ozonization chamber was very fast in a temperature range of 443 to 473 K, almost completed in a few tens of milliseconds. The decomposition of ozone into molecular oxygen was not significant, and one mole of ozone approximately reacted with one mole of NO. In addition, a kinetic study revealed that the ozonization method produces a negligible amount of byproducts such as NO3 and N2O5. The effect of the content of NO2 in NOx on the catalytic reduction efficiency was examined by adjusting the degree of NO oxidation in the ozonization chamber. The selective reduction of NOx to N2 by a monolithic catalyst (V2O5-WO3/TiO2) was largely enhanced when the content of NO2 was equal to that of NO, indicating that the mixture of NO and NO2 reacts faster than NO.