Simultaneous Removal of NOX and Particles from Diesel Engine Exhaust Using Plasma and Oxidative Catalyst

In this study, performance of a coaxial -type packed - bed plasma reactor was investigated for simultaneous removal of NO_X and diesel exhaust particles (DEP) from diesel exhaust. The plasma reactor was a concentric cylinder with a single layer of catalytic pellets (gamma-alumina or Pt -alumina) set between electrodes. Pulsed square high voltage was used. 6.0 L/min of diesel engine exhaust was used as the test gas, and space velocity was 36,000 hr^-1 in this plasma reactor. The pressure drop across the reactor was about 380-540 Pa. Experiment was carried out under rich oxygen gas conditions (13- 15%) and low temperature (423K). The DEP was collected by the catalytic pellets. NO was oxidized to NO₂ in the plasma and adsorbed by the catalytic pellets along with DEP. Exposing the catalysts to the pulsed plasma, collected DEP was continuously oxidized to CO₂. More than 95% of DEP (including sub-nano size particles) from diesel exhaust was collected and oxidized using plasma and catalyst. At the same time, NO_X and hydrocarbon were converted into N₂, CO₂and H₂O. 73% removal rate of NO_X was obtained in the test at low energy 43 J/L (44 eV/molecule NO). We found simultaneous removal effect continued for 20-30 minutes after switching off the plasma.