Essential Features of Gliding Arc Plasma for High-Performance Hydrocarbon Selective Catalytic Reduction of NO _x at Low Temperatures

The high removal efficiency of NO x fromdiesel engine exhaust gas at low temperatures remains challengingdue to the poor activity of catalysts under this condition. This workinvestigated the effectiveness of gliding arc plasma in the NO x removal over the Ag/gamma-Al2O3 catalyst with n-heptane as a reducingagent source for NO x reduction. The plasmaconjugated with the catalyst was performed like an injection method,i.e., a small part flow (1/26) that consisted of n-heptane was reformed to H-2 and oxygenated hydrocarbons(OHCs) by gliding arc plasma before mixing it with the gas containingNO( x ). Then, the overall gas was passedthrough the catalyst stage at various temperatures from 127 to 253 degrees C. The experimental data revealed that NO x removal efficiency significantly increased with plasma treatment.The enhancement by plasma treatment increased with temperature from127 to 226 degrees C, but the enhancement reduced at a temperature of253 degrees C. The result came from formation of H-2 and OHCsin the treated plasma gas, which reactivated NO x removal over the catalyst at low temperatures. Moreover, theenhanced NO x removal efficiency in a widelow-temperature range is obtained due to considerable hydrogen formationby the gliding arc plasma. To sum up, the highest NO x removal efficiency was 68.5% under a temperature of 226 degrees Cand specific energy input of 34.6 J/L, while it was 20.3% for thecatalyst alone; in other words, the removal efficiency increased by48.1% with using plasma under these conditions. Owing to its low energyconsumption, high-throughput gas treatment, and effectiveness at lowtemperatures, the technology is promising in practical applicationsfor refining diesel exhaust gases.