Reduction of nitrogen oxides by ozonization-catalysis hybrid process

Abstract

Treatment of nitrogen oxides (NOx) by using a hybrid process consisting of ozonization and catalysis was investigated. The ozonization method may be an alternative for the oxidation of NO to NO2. It was found that nitric oxide (NO) was easily oxidized to nitrogen dioxide (NO2) in the ozonization chamber without using any hydrocarbon additive. In a temperature range of 443 to 503 K, the decomposition of ozone into molecular oxygen was not significant, and one mole of ozone approximately reacted with one mole of NO. A kinetic study revealed that the oxidation of NO to NO2 by ozone was very fast, almost completed in a few tens of milliseconds. When the amount of ozone added was less than stoichiometric ratio with respect to the initial concentration of NO, negligible NO3 and N2O5 were formed. The oxidation of a part of NO to NO, in the ozonization chamber enhanced the selective reduction of NOx to N-2 by a catalyst (V2O5/TiO5), indicating that the mixture of NO and NO2 reacts faster than NO.