NOX removal in excess oxygen by plasma-enhanced selective catalytic reduction

In the off-gases of internal combustion engines running with oxygen excess, non-thermal plasmas (NTPs) have an oxidative potential, which results in an effective conversion of NO to NO2. In combination with appropriate catalysts and ammonia (NH3-SCR) or hydrocarbons (HC-SCR) as a reducing agent, this can be utilized to reduce nitric oxides (NO and NO2) synergistically to molecular nitrogen. The combination of SCR and cold plasma enhanced the overall reaction rate and allowed an effective removal of NOX at low temperatures. Using NH3 as a reducing agent, NOX was converted to N2 on zeolites or NH3-SCR catalysts like V2O5–WO3/TiO2 at temperatures as low as 100–200°C. Significant synergetic effects of plasma and catalyst treatment were observed both for NH3 stored by ion exchange on the zeolite and for continuous NH3 supply. Certain modifications of Al2O3 and ZrO2 have been found to be effective as catalysts in the plasma-assisted HC-SCR in oxygen excess. With an energy supply of about 30eV/NO-molecule, 500ppm NO was reduced by more than half at a temperature of 300°C and a space velocity of 20000h−1 at the catalyst. The synergistic combinations of NTP and both NH3- and HC-SCR have been verified under real diesel engine exhaust conditions.