Non-Thermal Plasma Activated deNOx Catalysis

The combination of non-thermal plasma (NTP) with catalyst systems as an alternative technology to remove NOx emissions in the exhaust of lean-burn stationary and mobile sources is reviewed. Several factors such as low exhaust gas temperatures (< 300 °C), low selectivity to N2 and the presence of impurities make current thermally activated technologies inefficient. Various plasma-catalyst systems have been examined and shown to have a synergistic effect on the de-NOx efficiency when compared with NTP or catalyst alone systems. The NTP is believed to form oxygenated species such as aldehydes, nitrogen-containing organic species and convert NO to NO2, which improves the reduction efficiency to N2 during hydrocarbon-selective catalytic reduction reactions. The NTP has been used as a pre-treatment to convert NO to its higher oxidation states such as NO2 or N2O5 to improve NOx reduction efficiency in the subsequent processes e.g. NH3-selective catalytic reduction. It has been applied to the lean phase of the NOx storage to improve the adsorption capacity of the catalyst by conversion of NO to NO2. Alternatively, a catalyst with high adsorption capacity is chosen and the NTP is applied to the rich phase to improve the reduction activity of the catalyst at low temperature.